1. The method for measuring and controlling the bonding strength of the precision glass mould pressing interface comprises the following steps: heating and soaking the top planar mold (101) and the bottom planar mold (102) and the glass sample (103);

-subjecting the top and bottom planar molds (101, 102) and the glass sample (103) to a pressing and holding operation;

-performing a de-binding operation on said top and bottom planar molds (101, 102) and said glass sample (103);

-subjecting the top and bottom planar molds (101, 102) and the glass sample (103) to a cooling and releasing operation;

wherein the debonding operation comprises maintaining a forming temperature while the bottom planar mold (102) and the glass sample (103) are moving downward at a debonding speed until a predetermined debonding distance is reached, or

Wherein the debonding operation comprises moving the bottom planar mold (102) and the glass sample (103) downward at a constant debonding speed until a pre-set debonding distance is reached; and simultaneously adjusting different forming temperatures to enable the glass sample (103) to be in a cohesive state, a bonding interface transition state and an interface fracture state respectively.

2. The precision glass press interface bond strength characterization and control method of claim 1, wherein the top planar mold (101) and the bottom planar mold (102) are used as a probe and a substrate, respectively.

3. The precision glass press interface bond strength characterization and control method of claim 1, wherein the top planar mold (101) and the bottom planar mold (102) are made of cemented carbide (WC) having a surface roughness Ra of about 2-5 nm.

4. The precision glass press interface bond strength characterization and control method of claim 1, wherein the glass sample (103) is a borosilicate glass BK7 in the form of a cylinder having a top and bottom surface roughness Ra of about 10-20 nm.

5. The precision glass press interface bond strength characterization and control method of claim 1, wherein the heating and soaking operation heats the top planar mold (101) and the bottom planar mold (102) and the glass sample (103) by infrared radiation at a rate of about 5-10 ℃/s; once the set constant molding temperature is reached, a soak is performed for approximately 60-120 seconds to determine the temperature uniformity within the glass cylinder.

6. The precision glass press interface bond strength characterization and control method of claim 1, wherein the pressing and holding operations achieve the same 1.5mm thickness reduction in about 120 seconds using a displacement control mode and hold the bottom planar mold (102) in the current position for about 60-90 seconds to relax the applied load to preclude a drop in the steep force from stress relaxation in adhesion measurements.

7. The precision glass press interface bond strength characterization and control method of claim 1, wherein the cooling and releasing operation; recording process parameters at a frequency of 1 Hz; and the minimum de-binding speed available to the former is 10 um/s.

8. The precision glass press interface bond strength characterization and control method of claim 1, wherein in the de-bonding operation, the force curve of the adhesion test is subtracted from the force curve of the reference test to obtain a functional relationship of tensile adhesion force F to de-bonding displacement Δ h; generally, the force-displacement curve is converted to a nominal stress-nominal strain curve using the following normalization method:

wherein A is₀Is the contact area between the glass and the mold before debonding, h₀Is the thickness of the glass sample before debonding, in this case, A₀＝πr²＝π*3.45²＝37.39mm²，h₀These key parameters, such as the maximum adhesion stress σ, are extracted from the nominal stress-strain curve at 3.50mm_maxMaximum tensile strain ε_maxAnd debonding work W_deb(unit is J/m)²) The calculation formula is as follows:

the thermodynamic work γ, which refers to the work of separating the interface and creating a new surface, called adhesion, is defined as follows if van der waals forces are only exhibited on the interface:

γ＝γ₁+γ₂-γ₁₂ (4)

wherein gamma is₁And gamma₂Is the surface energy of two contact bodies, gamma₁₂Is the interfacial energy, or, it is often combined with a given Young equation:

γ＝γ_Lv(1+cosθ) (5)

wherein gamma is_LVIs the surface tension of the liquid and theta is the contact angle, however, for debonding or fracture of soft materials, many researchers believe that the interfacial fracture energy can be given by empirical formulas due to the large energy consumption:

Г＝Г₀(1+Φ(α_Tv)) (6)

wherein phi (. alpha.) (_Tv) is a dissipation factor that depends on temperature and velocity, and Γ₀Is the threshold adhesion energy for crack velocity elimination; in the viscoelastic state, [ phi ] ([ alpha ])_Tv) > 1; the symbol r is used to characterize the inherent fracture energy associated with crack propagation, while W_debCan be considered as the apparent energy to break and as a structural property.

9. The precision glass press interface bond strength characterization and control method of claim 1, wherein

At a high temperature of 690 ℃ to 675 ℃, the glass sample (103) was extensively drawn like a cylinder, with significant necking; because of the limited debonding distance, the glass sample did not separate from the mold during debonding, being cohesive failure;

at a low temperature of 660 ℃ to 655 ℃, the glass sample (103) is completely separated from the mold along the interface in a clean manner, so that the upper surface and the lower surface of the glass sample (103) are flat, no visible deformation is seen, and the interface is broken;

at an intermediate temperature of 670 ℃ to 665 ℃, the debonding type is an interface in which considerable deformation of the glass sample (103) occurs; at least one of the surfaces is drawn as a protrusion with a singular profile, which is in contrast to a flat surface, a cohesive-interfacial transition.

10. The precision glass press interface bond strength characterization and control method of claim 1, wherein

For the cohesive failure state, the adhesion increased rapidly, passed through a maximum, and then decreased slowly throughout the degumming process; the tensile force becomes weak as the glass sample (103) becomes thin, i.e., the cross-sectional area of the sample becomes small; since the glass sample (103) did not detach from the mold at the end of the peeling, the adhesion did not drop to zero; a maximum nominal extension strain of about 1.10; in a cohesive failure state, the overall deformation of the glass sample (103) in the vertical direction is dominant, and the crack propagation on the interface is small;

for the cohesive-interfacial transition state, after the peak, the adhesion gradually decreases to zero over a wide range; due to the large separation distance, the glass sample (103) can be significantly stretched in the vertical direction, and the crack can continuously propagate along the interface; in the case of interfacial failure at low temperatures, the crack propagates rapidly, so that the adhesion drops abruptly to zero within a narrow distance of less than 100 μm, forming a steep adhesion curve.

11. The precision glass press interface bond strength characterization and control method of claim 1, wherein

Peak stress sigma in debinding operation_maxPossibly up to 1.4 MPa;

peak stress σ as temperature decreases_maxA significant increase in; the peak stress increase can be qualitatively illustrated by the following equation describing the adhesion between two flat elastic cylindrical solids in contact, as follows:

where γ is the work of adhesion, R is the effective radius of the interface, and K is the composite Young's modulus calculated using the form:

wherein E₁，E₂，v₁And v₂Respectively young's modulus and poisson's ratio, according to equation (7), the adhesion increases with increasing young's modulus of the contact body, and as the temperature decreases, the viscoelastic modulus of the glass increases greatly, and thus the adhesion increases.

12. The precision glass press interface bond strength characterization and control method of claim 11, wherein

Surface energy gamma based on molten soda-lime glass_LV≈0.35J/m²And in the WC dieHaving measured the contact angle of a moldable glass by using the formula γ ═ γ_LV(1+ cos θ) evaluation of adhesion γ of glass-WC interface₀Has a thermodynamic work of less than 0.18J/m²(ii) a Work of debonding W herein_debMuch greater than gamma₀；

Work of debonding W in the coherent state_debMore than 400J/m²The maximum value occurring at 675 ℃ is about 800J/m²(ii) a Debonding work W during the transition of bonding interface_debFalls in the range of 300-400J/m²Within the range of (1).

13. The precision glass press interface bond strength characterization and control method of claim 12, wherein

Excessive debonding work is mainly caused by viscous dissipation and strain energy stored in large volume deformations;

minimum debonding work W at 655 deg.C_debAbout 18.7J/m²(ii) a And peak stress sigma_maxHas different continuous increasing trend of_debIncreases and then sharply decreases with decreasing temperature;

debonding work W at cohesive state_aebThe reason for this increase is that the adhesion at lower temperatures is always greater at the same debonding displacement;

outside the cohesive state, despite the peak stress σ_maxThe effective debonding displacement is sharply reduced from more than 1000 microns to less than 100 microns, and the debonding work is integrally reduced.

14. The precision glass press interface bond strength characterization and control method of claim 1, wherein

In a debinding operation, the glass sample (103) is released from the mold at a speed of greater than 10 μm/s; as the debonding speed increases, the overall deformation caused by adhesion becomes significantly smaller;

and three types of debonding patterns are identified with respect to the debonding speed: wherein the content of the first and second substances,

at a debonding speed of 10 μm/s, the sample was in a cohesive state;

at a debonding speed of 20 to 40 μm/s, the sample is in a bonding interface transition state, the glass sample (103) is significantly deformed, and a bump is formed on the top surface;

when the debonding speed is 50 mu m/s, the debonding is in a complete interface state; and is

At low debonding speeds of 10 to 20 μm/s, the adhesion curve becomes blunted and slowly decreases; at high debonding speeds, the adhesion curve is sharp, dropping abruptly to zero.

15. The precision glass press interface bond strength characterization and control method of claim 1, wherein

De-binding work overall along with de-binding speed v_dIncrease and decrease:

the value of the debonding work at and near the cohesive state, i.e., a debonding speed of 10 to 20 μm/s, exceeds 470J/m²Large volume deformation occurs; since the glass sample was not separated from the mold at a speed of 10 μm/s, the calculated work of debonding at this time was less than the data at a speed of 20 μm/s;

in the transition state range of the bonding interface, the debonding work is maintained at 300J/m²Left and right;

for the interface state, the de-bonding work is reduced to 100J/m²The following.

16. The precision glass press interface bond strength characterization and control method of claim 1, wherein

When the temperature is reduced or the debonding speed is increased, the crack speed increases significantly:

in the interpolymerized state, the crack velocity is very slow, about 100 μm/s; but outside the cohesive state, the crack velocity v_cVery fast growth, e.g. at 655 ℃ and v_dAt 50 μm/s, the growth rate is about 10³μ m/s; in the cohesive state, the crack speed is slower than the debonding speed, i.e. the glass sample (103) is prone to vertical deformation;

outside the cohesive state, the crack velocity is much faster than the debonding velocity, i.e. crack propagation along the interface becomes dominant;

using reduced crack velocity is crackingVelocity v of the pattern_cWith a temperature deviation factor alpha_TThe product of (a);

the relationship between debonding temperature and crack velocity was determined using the following Arrhenius equation:

logα_T＝(ΔH/2.303R)(1/T-1/T_ref) In which α is_TFor the temperature offset factor,. DELTA.H/R.20730 and T_ref＝680℃。

17. The precision glass press interface bond strength characterization and control method of claim 16, wherein

The glass sample (103) exhibits a soft viscoelastic material at a reduced crack velocity a at higher temperatures or/and lower crack velocities_Tv_cAt a lower level, a large amount of viscous dissipation causes W_debThe content is very high;

with decreasing crack velocity a_Tv_cThe cohesive-interfacial transition range occurs first; may still be high due to the enhanced viscoelastic dissipation;

reduced crack velocity a at high levels_Tv_cThe glass sample (103) tends to behave as an elastic solid, the debonding type is an interface state, and the debonding work is much lower than the cohesive and interface state states;

furthermore, at high separation rates, the fracture energy Γ (V) is a decreasing function proportional to the inverse of the crack velocity:

18. the precision glass press interface bond strength characterization and control method of claim 17, wherein

The crack length L is 3.45mm, λ is about 104 which is the ratio of E ″ and E' of BK7 glass 35, and the stress relaxation time τ (680 ℃) is 0.003s, so L/λ τ is about 115 μm/s.

19. The precision glass press interface bond strength characterization and control method of claim 16, wherein

The transition condition between cohesive viscous deformation and interfacial debonding is predicted by the following equation:

that is, for Γ > Eh, the initial defects will spread primarily in the majority of the adhesive layer, where E and h are the young's modulus and the thickness of the adhesive layer;

at a lower reduced crack velocity a_Tv_cThe glass behaves like a soft viscoelastic material, the temperature and frequency dependent relaxation modulus E (T, ω) of which can be rapidly reduced to very small values, while the debonding work is too high, so as to satisfy the conditions for the deformation of the internal polymer;

with decreasing crack velocity a_Tv_cThe debonding work decreases, while the relaxation modulus E (T, ω) increases, so their ratio decreases more rapidly; the overall deformation of the inner polymer will gradually translate into interfacial detachment.

Background

The optical glass compression molding technology is a precision duplicating molding technology. Compared with the traditional processing technology, such as polishing and grinding, the method has the advantages of one-step forming, high efficiency, low cost, suitability for batch production and the like. With the increasingly widespread use of high-precision optical glass lenses, the technology is rapidly developed.

The glass molding technology is used for heating and pressurizing glass and a mold, and molding optical glass into optical parts capable of meeting specific requirements at one time, and relates to various challenges such as mold materials, glass materials, relevant equipment and process parameters and the like. The ultra-precise manufacturing of the micro-nano array mold is the primary foundation for realizing the ultra-precise forming technology.

Another important step of the glass molding technology is that the glass material and the mold are heated to a temperature above the glass conversion temperature, the molding pressure is controlled to copy the surface shape of the micro-nano array mold to the surface of the glass, and then the optical micro-nano array glass sheet is cooled and taken out. In the process, because the thermal expansion coefficients of the mold material and the optical glass material are different, the factors such as a stress field, a temperature field, a rheological field and the like can cause forming errors, and the nickel phosphide coating of the mold and the high-viscosity glass are easy to generate the phenomena of molecular diffusion, affinity fusion and adhesion bonding under the high-temperature and high-pressure environment.

Aiming at the phenomenon that an interface bonding separation action mechanism and element diffusion exist between a nickel phosphide microstructure of a mould and high-temperature, high-pressure and high-viscosity hot-melt glass due to a micro-nano surface effect in a mould pressing forming process, an iridium/rhenium (lr/Re) noble metal coating is plated on the surface of a processed nickel phosphide coating micro-groove mould by adopting a Physical Vapor Deposition (PVD) method in the prior art, so that the friction coefficient between the glass and the mould interface can be reduced, the phenomenon that phosphorus elements in the nickel phosphide coating in the mould diffuse to the glass surface is isolated, and the service life of the mould is prolonged.

Disclosure of Invention

The invention aims to provide a new method for realizing different debonding effects by changing temperature and debonding speed by utilizing the relationship between the quality of an optical element and the adhesion force of a glass mold in glass precision forming, thereby improving the quality of optical element forming and prolonging the service life of a noble mold.

The invention provides a method for representing and controlling bonding strength of a precision glass mould pressing interface, which comprises the following steps:

heating and soaking the top planar mold (101) and the bottom planar mold (102) and the glass sample (103);

-subjecting the top and bottom planar molds (101, 102) and the glass sample (103) to a pressing and holding operation;

-performing a de-binding operation on said top and bottom planar molds (101, 102) and said glass sample (103);

-subjecting the top and bottom planar molds (101, 102) and the glass sample (103) to a cooling and releasing operation;

wherein the debonding operation comprises maintaining a forming temperature while the bottom planar mold (102) and the glass sample (103) are moving downward at a debonding speed until a predetermined debonding distance is reached, or

Wherein the debonding operation comprises moving the bottom planar mold (102) and the glass sample (103) downward at a constant debonding speed until a pre-set debonding distance is reached; and simultaneously adjusting different forming temperatures to enable the glass sample (103) to be in a cohesive state, a bonding interface transition state and an interface fracture state respectively.

Drawings

In order to more clearly illustrate the technical solution in the embodiments of the present invention, the drawings required to be used in the embodiments will be briefly described below. It is obvious that the drawings in the following description are only examples of the invention, and that for a person skilled in the art, other drawings can be derived from them without making an inventive step.

FIG. 1(a) is a schematic diagram of the steps for performing a probe tack test using the present invention;

FIG. 1(b) is a graph of the internal temperature of the bottom planar mold 102, the measured contact force, and the position of the bottom planar mold 102 of the present invention as a function of time;

FIG. 2(a) is a graph of the relationship between the position of the bottom planar mold and the measured force of one embodiment of the present invention;

FIG. 2(b) is an adhesion displacement and corresponding nominal stress-strain curve obtained according to an embodiment of the present invention;

FIGS. 3(a) and (b) are the results of debonding experiments using the method of the present invention at different forming temperatures. In which fig. 3(a) is a photographic image of a glass sample obtained by the method of the present invention at different temperature examples, the glass sample being deformed by adhesion during debonding. FIG. 3(b) is a plot of adhesion versus displacement and equivalent nominal stress versus strain obtained from a debonding experiment performed at different test temperature examples using the method of the present invention;

FIG. 4 is a graph of peak stress and work-to-debond as a function of temperature decrease in the method of the present invention;

FIGS. 5(a) and (b) are the results of debonding experiments using the method of the present invention at different debonding rates. Wherein, fig. 5(a) is a photograph of a glass sample obtained by the method of the present invention at the same temperature but different debonding speed, the glass sample being deformed by adhesion during the debonding. FIG. 5(b) is a plot of adhesion versus displacement and equivalent nominal stress versus strain obtained from a debonding experiment conducted at the same temperature and at different debonding speeds using the methods of the present invention;

FIG. 6 is a graph showing the results of experiments on peak stress and debonding work at different debonding speeds at a certain experimental temperature using the method of the present invention;

FIGS. 7(a) and 7(b) are schematic graphs of calculated crack velocities for temperature experiments and debond velocity experiments according to the methods of the present disclosure;

FIGS. 8(a) - (b) illustrate peak bond stress σ for one embodiment of the method of the present invention_maxAnd debonding work W_debA relationship diagram of (1);

fig. 8(c) shows the transition conditions between the different debonding types demonstrated by the method of the present invention.

Detailed Description

Specific embodiments of the present invention will now be described with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. These embodiments are provided only for the purpose of exhaustive and comprehensive description of the invention so that those skilled in the art can fully describe the scope of the invention. The terminology used in the detailed description of the embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention.

The invention provides a novel glass press forming method by studying the debonding behavior (debonding defects) of a typical glass molding interface, and utilizes the peak bond strength sigma to produce a glass with a high degree of adhesion_maxAnd a debonding power W_debThe relationship between them characterizes the debonding behavior.

Adhesion or bonding of glass to a mold in glass hot forming techniques (e.g., hot glass stamping techniques, glassware manufacturing techniques, and Precision Glass Molding (PGM) techniques.) because of the long-lasting contact at high temperatures and/or pressures, the adhesion of glass to the mold is primarily a result of chemical reactions and diffusion at the interface. Most of the difficulties are not due to filling of the mould but to demoulding. With PGM technology, adhesion can result in minute island glass residues on the mold, thereby degrading the quality of precious mold and molded optical element surfaces.

Important details of release studies include quantification of adhesion by standard test procedures and quantification of the strength of the paste using "adhesion time". It is also included to characterize the adhesion strength by using the maximum pull during separation to define the "demold force". Since the demolding process is then usually carried out under cooling, the measured demolding force is a cumulative result depending on the cooling history, and it is therefore not reasonable to establish a direct relationship between demolding force and temperature. In addition, evaluation of the separation process by only the mold release force cannot reflect the change of the separation process and the separation mechanism. In addition to the release force, the energy to break is a necessary condition to describe the adhesion strength and debonding mechanism; further, in addition to the contact state before separation, the conditions at the time of separation also affect the mold release force, such as the cooling time and the cooling temperature. Further, the cooling rate is hidden behind the release temperature, which is the exact release temperature, when the release temperature is located in the vicinity of the glass transition temperature region. This is because the debonding behavior of soft materials depends not only on the interfacial interactions but also on the rheological properties.

The present invention essentially employs a process of probing a typical glass molding interface to fully describe the debonding behavior between the glass and the mold by combining the adhesion evolution curve, peak stress and debonding activity. The present invention mainly adopts the expression "de-bonding process" instead of the "de-bonding process" because the de-bonding process is usually accompanied by cooling, whereas the de-bonding process of the present invention is performed at a specific forming temperature and speed, and utilizes the effect of the de-bonding temperature and speed on the de-bonding process, and the de-bonding temperature and speed are analyzed from the viewpoint of reducing the crack speed.

FIG. 1(a) is a schematic diagram of the steps for performing a probe tack test using the present invention. In which a glass sample 103 is placed between a top planar mold 101 and a bottom planar mold 102, wherein the top planar mold 101 and the bottom planar mold 102 serve as a probe and a substrate, respectively. In one embodiment, a mold made of cemented carbide (WC) was mirror polished to a good surface roughness Ra of about 2 nm. In another example, the glass sample was borosilicate glass BK7 in the form of a cylindrical cylinder having a diameter of 6.0 millimeters and a thickness of 5.0 millimeters, and the roughness values Ra of the top and bottom surfaces of the glass cylinder were about 10 nm.

In step 110, the top and bottom flat molds 101 and 102 and the glass sample 103 are heated and soaked; in one embodiment, the component is heated by infrared radiation at a rate of about 5 ℃/s. Once the set molding temperature is reached, a 60 second soak will be performed to ensure uniform temperature within the glass cylinder.

In step 111, the top and bottom flat molds 101 and 102 and the glass sample 103 are pressed and held; in one embodiment, the same 1.50mm thickness reduction in 120 seconds can be achieved with the displacement control mode during the pressing stage, which ensures that the formed shape before debonding is almost the same for different trials. To exclude the drop in the sharp force caused by stress relaxation from the adhesion measurement, after the pressing step, the bottom mold was held in its current position for 60 seconds to relax the applied load.

In step 112, a step of debonding the top and bottom flat molds 101 and 102 and the glass sample 103; in one embodiment, the forming temperature is maintained while the bottom planar mold 102 is at a constant de-bonding speed V_dAnd moving downwards until a preset debonding distance is reached.

Thereafter, in step 113, the above-described top and bottom flat molds 101 and 102 and the glass sample 103 are subjected to cooling and releasing operations, which are performed as conventional steps; in one embodiment, process parameters (e.g., temperature, force, and position) are recorded at a frequency of 1 Hz; in one embodiment, the minimum de-bonding speed available to the forming machine is 10 μm/s.

Fig. 1(b) is a graph of the internal temperature of the bottom planar mold 102, the measured contact force, and the position of the bottom planar mold 102 of the present invention as a function of time. Wherein at the debonding position 104, i.e. at the beginning of the debonding step 103, it is evident that there is an adhesion phenomenon between the glass sample 103 and said top planar mold 101.

Fig. 2(a) is a graph showing the relationship between the position of the bottom flat mold and the measurement force according to one embodiment of the present invention. Wherein the forming temperature is 655 ℃ and the debonding speed is 10 μm/s, a reference test is applied in order to exclude the frictional forces from the adhesive forces. The solid line in fig. 2(a) represents the force in the tack test, the broken line represents the force of the reference test, represents the pressing and holding step of step 111 and the debonding step of step 112 described above, in which the positional relationship between the position of the bottom flat mold and the top flat mold gradually increases as the pressing step is performed in the direction of arrow 201, the holding step is performed in the direction of arrow 202, and the debonding step is performed following the direction of arrow 203; at the debond position 204, there is a clear indication of adhesion between the glass sample 103 and the top planar mold 101. The difference between the viscosity test value and the reference value is exactly the interaction force between the glass and the mould. On the abscissa is the molding force, while on the abscissa is the adhesion force. It should be noted that the bottom planar mold does not develop adhesion immediately after retraction, primarily because a small gap (about 100 μm) is intentionally left between the mold insert and the mold to avoid direct hard contact. Furthermore, outside the glass mold interaction region, it can be observed that the two curves can closely overlap each other due to the extraordinary repetitive motion properties of the machine, thus ensuring the accuracy of the relative forces.

Fig. 2(b) is an adhesion displacement and corresponding nominal stress-strain curve obtained according to an embodiment of the present invention. In fig. 2(b) the force curve of the tack test is subtracted from the force curve of the reference test during debonding to obtain the tensile adhesion force F as a function of the debonding displacement Δ h. Generally, the force-displacement curve is converted to a nominal stress-nominal strain curve using the following normalization method:

wherein A is₀Is the contact area between the glass and the mold before debonding, h₀Is the thickness of the glass sample before debonding. Here, A is₀＝πr²＝π*3.45²＝37.39mm²，h₀3.50 mm. These key parameters, such as the maximum adhesion stress σ, are extracted from the nominal stress-strain curve_maxMaximum tensile strain ε_maxAnd debonding work W_deb(unit is J/m)²) The calculation formula is as follows:

the thermodynamic work γ, which refers to the work of separating the interface and creating a new surface, called adhesion, is defined as follows if van der waals forces are only exhibited on the interface:

γ＝γ₁+γ₂-γ₁₂ (4)

wherein gamma is₁And gamma₂Is the surface energy of two contact bodies, gamma₁₂Is the interface energy. Alternatively, it is often combined with a given Young equation:

γ＝γ_LV(1+cosθ) (5)

wherein gamma is_LVIs the surface tension of the liquid and θ is the contact angle. However, for debonding or fracture of soft materials, many researchers believe that the interfacial fracture energy can be given by empirical formulas due to the large energy consumption:

Γ＝Г₀(1+Φ(α_Tv)) (6)

wherein phi (. alpha.) (_TV) is a dissipation factor that depends on temperature and rate, and Γ₀Is the threshold adhesion energy for crack velocity elimination. Usually, in the viscoelastic state,. phi. (. alpha.)_Tv) > 1. It is worth noting that the symbol Γ is used to characterize the inherent fracture energy associated with crack propagation, whereas W is_debCan be considered as the apparent energy to break and as a structural property.

As an analysis of the experimental results of the method employed in the present invention, the temperature-dependent debonding behavior is intensively discussed below. The debonding experiments were performed in the range of 690 ℃ to 655 ℃ according to the typical forming temperature range of BK7 glass. Since the adhesion effect is more pronounced at high temperatures, the temperature experiment and the following experimental results are discussed in descending order. In one embodiment, the same debonding speed of 10 microns/second and apparent debonding distance of 4.0 millimeters was used for all cases.

FIGS. 3(a) and (b) are the results of debonding experiments using the method of the present invention at different forming temperatures. In which fig. 3(a) is a photographic image of a glass sample obtained by the method of the present invention at different temperature examples, the glass sample being deformed by adhesion during debonding. Fig. 3(b) is an adhesion-displacement and equivalent nominal stress-strain curve obtained by a debonding experiment performed using the method of the present invention at different test temperature examples. Three types of debonding modes are distinguished in terms of the deformation mode according to the debonding temperature. (1) This type is called cohesive failure (2) at low temperatures (660 ℃ and 655 ℃) the glass sample can be completely separated from the mold in a clean manner along the interface, making the upper and lower surfaces of the glass sample flat and without visible distortion, and this type is called interfacial fracture (3) at intermediate temperatures (670 ℃ and 665 ℃) the debonding type is an interface, but with considerable distortion of the glass sample during debonding. And is not ideal for propagation of an axisymmetric crack from the edge to the center. Thus, the drawn glass sample is generally not axisymmetric, but may be tilted in any direction.

The debonding behavior, e.g., adhesion/stress evolution, peak adhesion stress, and debonding work, of these three debonding types are all significantly different. Fig. 3(b) is an adhesion-displacement and equivalent nominal stress-strain curve obtained by a debonding experiment performed at different temperatures using the method of the present invention. For cohesive failure, adhesion increases rapidly, passes through a maximum, and then decreases slowly throughout the degumming process. The main reason for the reduction is that the glass sample becomes thin, i.e. the cross-sectional area of the sample becomes small, resulting in a weakened tension. Moreover, with further extensive elongation, thinning eventually progresses to a noticeable necking phenomenon. As described above, since the glass sample did not detach from the mold at the end of peeling, the adhesion force did not drop to zero. Here, the maximum nominal extension strain is about 1.10. It is reasonable to believe that for cohesive failure, the bulk deformation of the glass sample in the vertical direction is dominant and crack propagation at the interface appears to be small. For the cohesive-interfacial transition state, the adhesion gradually decreases to zero over a wide range after the peak. Due to the large separation distance, the glass sample is significantly stretched in the vertical direction, and the crack continues to propagate along the interface, thereby leading to a singular protrusion. In contrast, in the case of interfacial failure at low temperatures, the crack propagates rapidly, so that the adhesion drops abruptly to zero within a narrow distance (less than 100 μm), forming a steep adhesion curve. The location of the peak force generally corresponds to the onset of crack propagation. In addition, the glass sample may be finely stretched before the peak force, which may confirm that the final thickness of 3.58mm is slightly greater than expected.

According to the adhesion curve in FIG. 3(b), the peak nominal stress σ_maxThe graph plotted against the reverse order temperature is shown in fig. 4. FIG. 4 is a graph of peak stress and work-to-debond as a function of temperature in the method of the present invention. First, the peak stress σ during debonding_maxPossibly up to 1.4 MPa. More importantly, as the temperature decreases, the peak stress σ_maxA significant increase was observed. The cause of the increase in peak stress can be qualitatively illustrated by the following equation describing the adhesion between two flat elastic cylindrical solids in contact, as follows:

where γ is the work of adhesion, R is the effective radius of the interface, and K is the composite Young's modulus calculated using the form:

wherein E₁，E₂，v₁And v₂Young's modulus and poisson's ratio, respectively. According to equation (7), the adhesion increases with the Young's modulus of the contact bodyBut is increased. When the temperature is lowered, the viscoelastic modulus of the glass greatly increases, and thus the adhesion increases. Some researchers believe that the separation force increases at the moment of separation as the glass temperature decreases. Some researchers believe that the "interface" temperature leads to the opposite conclusion. This discrepancy can be attributed to differences in experimental conditions and the concept of temperature used. In addition, it is noteworthy that in the interpolymerized state, the peak stress is relatively low, which may explain why the interfacial bonds are not separated. It appears that the stress criterion can be used to determine whether separation can be achieved at the interface.

In addition, FIG. 4 plots the work of debonding W at various temperatures_deb. Surface energy gamma based on molten soda-lime glass_LV≈0.35J/m²And the contact angle of the moldable glass measured on a WC mold by using the formula γ ═ γ_LV(1+ cos θ) evaluation of adhesion γ of glass-WC interface₀Has a thermodynamic work of less than 0.18J/m². However, here, the work of debonding W_debMuch greater than gamma₀. In particular, the work of debonding W in the coherent state_debMore than 400J/m²The maximum value occurring at 675 ℃ is about 800J/m². Debonding work W during the transition of bonding interface_debFalls in the range of 300-400J/m²Within the range of (1). These values are at least compared to gamma₀Three orders of magnitude greater.

As shown in fig. 3(a), excessive debonding energy is primarily caused by viscous dissipation and strain energy stored in the bulk deformation. Minimum debonding work W even at 655 deg.C_debAbout 18.7J/m²Still, it is implied that the adhesion between the glass and the mold is not negligible. On the other hand, with the peak stress σ_maxHas different continuous increasing trend of_debIncreasing and then decreasing sharply with decreasing temperature. Debonding work W at cohesive state_debThe reason for this increase is that the adhesion at lower temperatures is always greater at the same debond shift. Outside the cohesive state, despite the peak stress σ_maxThe effective debonding displacement increases, but decreases dramatically from over 1000 microns to under 100 microns, so the overall work of debonding decreases.

Finally, since in FIG. 4Peak stress σ of_maxThe curve increases monotonically with decreasing temperature, so it is difficult to determine these three stripping regimes. On the contrary, the energy can be released by the debonding work W_debSharp discontinuities in the curve clearly distinguish the transitions. In addition, the debonding work W_debIs more sensitive to temperature. As a result, we can easily remove the work W from the adhesive_debCurves other than from peak stress σ_maxThree debonding modes were identified in the curves.

The following describes the debonding experiments relating to the debonding speed. FIGS. 5(a) and (b) are the results of debonding experiments using the method of the present invention at different debonding rates. Fig. 5(a) is a photograph of a glass sample, which is deformed by adhesion during debonding, obtained by the method of the present invention at the same temperature and at different debonding speeds. Fig. 5(b) is an adhesion-displacement and equivalent nominal stress-strain curve obtained from a debonding experiment performed using the method of the present invention at the same temperature and at different debonding speed examples. FIG. 6 is a graph showing the results of experiments on peak stress and debonding work at different debonding speeds at a certain experimental temperature using the method of the present invention.

Experiments were performed at 680 c with five debonding speeds ranging from 10 microns/second to 50 microns/second. Combining the photographs and the adhesion curves in FIGS. 5(a) and 5(b), the debonding speed v_dAlso plays an important role in the debonding behavior. During the debonding process, the glass sample was released from the mold at a speed of greater than 10 μm/s. With the speed v of debonding_dThe overall deformation caused by adhesion becomes significantly smaller. Again, with respect to the debonding velocity v_dThree types of debonding patterns are identified. As previously mentioned, at a debonding speed of 10 μm/s, the sample was in a cohesive state. At a debonding speed of 20 to 40 μm/s, the sample was in a bonding interface transition state because the glass sample was significantly deformed and a bump was formed on the top surface. When the debonding speed was 50 μm/s, the debonding was in a complete interface state. Similarly, the adhesion-displacement curve and the equivalent stress-strain curve at different debonding velocities v_dThe process is clearly different. At low debonding speed v_d(10 and 20 μm/s), the adhesion curve becomes dull and slowly decreases. In contrast, at high debonding speeds v_dAt this point, the curve is sharp and drops abruptly to zero.

The peak adhesion stress σ is plotted in FIG. 6_maxThe sum of results in v_dAs a result of the work of debonding. Subentries as observed in FIG. 5(a) (b) at peak stress σ_maxAll the strain values are about 0.01, so the strain ratesIn this small strain range with v_dAnd is increased. Since the stress response of viscoelastic materials is highly dependent on strain rate, tods, and thus can qualitatively explain why the peak stress σ_maxWith the speed v of debonding_dFrom 0.3MPa to 1.5 MPa. And, the peak stress σ_maxAfter 40 μm/s, tends to grow slowly.

Similarly, despite the peak stress σ_maxWith the speed v of debonding_dThe effective debonding distance is increased, but significantly decreased in fig. 5. Therefore, the debonding work W_debOverall velocity of debonding v_dIncreasing and decreasing. In detail, at and near the cohesive state (i.e. the debonding velocity v)_dAt 10 and 20 μm/s), the debonding work W_debIs too large (more than 470J/m)²) So that large-volume deformation occurs. Since the glass sample was not separated from the mold at a speed of 10 μm/s, the work of debonding W calculated at this time_debLess than the data at a speed of 20 μm/s. Within the transition state range of the bonding interface, the debonding work W_debMaintained at 300J/m²Left and right. For the interface state, it drops to 100J/m²The following.

According to the evolution trend and the debonding work W_debAgain, these three debonding modes are distinguished. However, it is still basically necessary to cope with the peak stress σ_maxAn evaluation was performed to fully characterize the debonding process. For example, the debonding speed v is compared_dIn the case of 10 μm/s and 20 μm/s, their work of debonding W_debThe values are all high, however, the separation occursSpeed of debonding v_d20 μm/s. This may be due to the speed of debonding v_dThe debonding work W at 20 μm/s_debAbove some stress limit beyond which the interfacial bond may be broken. The evolution process of the adhesion force, the peak adhesion stress and the debonding power are amplified together so as to fully characterize the debonding process.

The transition between viscous bulk deformation and interfacial fracture is described below. Fig. 7(a) and 7(b) are schematic diagrams of calculated crack velocities for temperature experiments and debonding velocity experiments according to the methods of the present invention. As shown in FIGS. 7(a) and 7(b), when the temperature is lowered or the debonding speed v_dIncreased crack velocity v_cIs remarkably increased. In the agglomerated state, the crack velocity v_cVery slow, about 100 μm/s; but outside the cohesive state, the crack velocity v_cVery fast growth, e.g. at 655 ℃ and v_dAt 50 μm/s, the growth rate is about 10³μ m/s. Furthermore, it was found that in the agglomerated state, the crack velocity v_cSpecific debonding velocity v_dSlow, which means that the glass samples are prone to vertical deformation. However, in addition to the agglomerated state, the crack velocity v_cSpecific debonding velocity v_dMuch faster, which means that crack propagation along the interface becomes dominant. Therefore, comparing the crack velocity and the debonding velocity is very useful for understanding the deformation tendency of the glass samples.

Since the crack velocity varies significantly with the debonding temperature, the effect of temperature on the debonding properties is compounded. By using a reduced crack velocity, which is the crack velocity v_cWith a temperature deviation factor alpha_TThe effect of debonding temperature and crack velocity can be analyzed from an overall perspective. The displacement factor here is given by the Arrhenius equation log alpha_T＝(ΔH/2.303R)(1/T-1/T_ref) Wherein Δ H/R is 20730 and T_refReported data for glass BK7 were used at 680 ℃.

FIGS. 8(a) - (b) illustrate peak bond stress σ for one embodiment of the method of the present invention_maxAnd debonding work W_debA graph of the relationship (A) between the crack velocity log (a) and the crack velocity log (a) as logarithmic decrease_Tv_c) As a function of (c). In the figurePoints are data of temperature experiments, while squares are dates of speed experiments; in addition, closed is the cohesive type, open is the other two types; fig. 8(c) shows the transition conditions between the different debonding types demonstrated by the method of the present invention.

FIG. 8(a) shows the maximum viscous stress σ_maxFollows log (a) in a manner tending to be linear_Tv_c) Is remarkably increased. In addition, the maximum viscous stress σ_maxIt appears to be more sensitive to an increase in the rate of debonding, the results of which are indicated by the square marks. The gap between the closed mark and the open mark in fig. 8(a) may be the threshold stress above which the glass sample can be successfully separated from the mold, falling within the narrow range of 0.5-0.6 MPa. In FIG. 8(b), log (a) is plotted_Tv_c) Function of debonding work W_debAnd (6) obtaining the result. When the temperature is higher or/and the crack velocity v_cAt lower levels, the glass behaves as a soft viscoelastic material at reduced crack velocities a_Tv_cAt a lower level, W is due to a large amount of viscous dissipation_debThe content is very high. With decreasing crack velocity a_Tv_cThe cohesive-interfacial transition range occurs first. This may still be high due to the enhanced viscoelastic dissipation. Reduced crack velocity a at high levels_Tv_cHere, the glass tends to behave as an elastic solid, so that the debonding type is an interface state, and the debonding work W_debMuch lower than the first two states. Therefore, the debonding work W is mainly judged_debDrastic change in size and log (a) of log_Tv_c) Three debonding modes can be clearly identified.

Furthermore, based on an in-depth analysis of the dissipation process, at high separation rates, the fracture energy f (V) is a decreasing function proportional to the inverse of the crack velocity:

in one embodiment, the crack length L is 3.45mm,is the ratio of E ″ and E' of BK7 glass 35, and the stress relaxation time τ (680 ℃), is 0.003s, so L/λ τ is about 115 μm/s. The debonding work W according to the linearly fitted curve in FIG. 8(b)_debThe resulting medium-high level fits well with the theoretical prediction in equation (9).

Fig. 8(c) shows the transition condition between cohesive viscous deformation and interfacial detachment. In a comprehensive review of the adhesion of soft materials, it can be concluded that this transition can be predicted roughly by the following equation:

that is, for Γ > Eh, the initial defects will be mainly spread in the majority of the adhesive layer, where E and h are the young's modulus and the thickness of the adhesive layer. As mentioned above, at a lower reduced crack velocity a_Tv_cThe glass behaves like a soft viscoelastic material, whose temperature-and frequency-dependent relaxation modulus E (T, ω) can be rapidly reduced to very small values, while the debonding work W_debIt is too high so that the condition for deforming the inner polymer is easily satisfied. With decreasing crack velocity a_Tv_cIncrease of (2), debonding work W_debDecreases, while the relaxation modulus E (T, ω) increases, so their ratio decreases more rapidly. As a result, the overall deformation of the inner polymer will gradually be transformed into interfacial detachment. Therefore, equation (10) qualitatively explains the transition conditions of the present invention in terms of both viscoelasticity and work-to-debond.

The above description is only for the purpose of illustrating the present invention, and any person skilled in the art can modify and change the above embodiments without departing from the spirit and scope of the present invention. Therefore, the scope of the claims should be accorded the full scope of the claims. The invention has been explained above with reference to examples. However, other embodiments than the above described are equally possible within the scope of this disclosure. The different features and steps of the invention may be combined in other ways than those described. The scope of the invention is limited only by the appended claims. More generally, those of ordinary skill in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are exemplary and that actual parameters, dimensions, materials, and/or configurations will depend upon the particular application or applications for which the teachings of the present invention is/are used.