A method for predicting mechanical parameters of composite materials

Abstract

This invention provides a method for predicting the mechanical parameters of composite materials. The elastic modulus and Poisson's ratio of polyetheretherketone (PEEK) samples are measured. Combined with the mechanical parameters of carbon fiber, the mechanical parameters of carbon fiber-reinforced PEEK composite materials are derived. The mechanical parameters of carbon fiber-reinforced PEEK composite samples are then measured, and the obtained elastic modulus, shear modulus, and Poisson's ratio are compared with the derived values ​​to verify their reliability and make corrections. Based on the technical solution of this invention, a prediction model for the crystallinity and mechanical properties of PEEK and carbon fiber-reinforced PEEK composites was established. The accuracy of the model was verified through DSC, tensile, and shear tests.

Description

Technical Field

[0001] The present invention relates to the technical field of composite material mechanical parameter prediction, and in particular to a composite material mechanical parameter prediction method. Background Art

[0002] Polyetheretherketone (PEEK) exhibits excellent high-temperature mechanical properties and biocompatibility. It can be used to prepare thermoplastic composites with excellent heat resistance, high specific modulus, high specific strength, lightweight construction, repairability, and recyclability, showing potential applications in aerospace, construction, medicine, and the automotive sector. The manufacturing process of PEEK and its composites often involves temperature fluctuations. For example, during molding or 3D printing, the material must be heated to near-fluid temperature (approximately 400°C). During drilling, heat accumulates axially, leading to localized high temperatures (above the melting point) near the hole exit, affecting the circumferential stress distribution and the component's safety and lifespan. These temperature fluctuations cause the resin matrix to undergo two or three mechanical state transitions. These changes manifest themselves microscopically as the thawing and rearrangement (recrystallization) of molecular chains. The crystallinity of PEEK can range from almost complete absence of crystallinity (0%) to optimal crystallinity (approximately 48%). The material's crystallization behavior is closely related to its macroscopic thermodynamic properties. Therefore, the influence of process parameters on the crystallinity, mechanical properties and product quality of polyetheretherketone and its composite materials is a hot topic of research at present, and certain research results have been achieved in the fields of applied research and basic theoretical research.

[0003] In the field of fundamental research on polymer crystallization dynamics, numerous scholars have conducted in-depth studies on the crystallization dynamics and mechanisms of polymer molding processes. This research aims to clarify the inherent nature of material crystallization behavior, thereby further understanding the influence of process parameters on material crystallinity and mechanical properties, thus guiding manufacturing. Both crystallization temperature and crystallinity are constrained by the cooling rate. In particular, when the cooling rate exceeds the polymer crystallization rate, the crystallinity decreases significantly and the crystal morphology changes.

[0004] Existing research results have clarified the influence and influencing mechanism of process parameters on the crystallinity and mechanical properties of materials, but have ignored the influence of the maximum temperature reached by the material on the crystallization behavior. There is a general lack of quantitative research, and there is a lack of correlation and mathematical model between process parameters and crystallinity and mechanical properties, making it impossible to predict the crystallinity and mechanical properties under certain process parameters.

[0005] Therefore, the main content of this study is to explore the influence of the maximum temperature and cooling rate of the material on the crystallization behavior of polyetheretherketone and CF / PEEK, establish the correlation and mathematical model between process parameters and crystallinity and mechanical properties, and thereby regulate and optimize product quality. This paper simulates the non-isothermal experimental conditions in actual production, discusses the crystallization behavior of polyetheretherketone and carbon fiber reinforced polyetheretherketone composites at different maximum temperatures and cooling rates, analyzes the influence mechanism of processing parameters on the crystallization behavior and mechanical properties of materials, and establishes the crystallinity and mechanical property prediction models of polyetheretherketone and carbon fiber reinforced polyetheretherketone composites respectively. The accuracy of the model is verified by DSC test, quasi-static tensile test and shear test, providing a good reference and suggestion for the selection of processing parameters for polyetheretherketone and carbon fiber reinforced polyetheretherketone composites. Summary of the Invention

[0006] In response to the above problems in the prior art, this application proposes a method for predicting mechanical parameters of composite materials, comprising the following steps:

[0007] Step 1: Based on the thickness of the carbon fiber reinforced polyetheretherketone composite material and whether it is a rigid body, the sample type is selected. The polyetheretherketone sheet is cut into tensile standard parts using a cutting machine and placed in a customized mold. Based on the thermal history of the polyetheretherketone material during the crystallinity test, the polyetheretherketone tensile parts are subjected to pressure-maintaining heat treatment in a hot press. After heating to a predetermined temperature, they are cooled to room temperature at different cooling rates.

[0008] Step 2: Measure the elastic modulus and Poisson's ratio of the polyetheretherketone sample, and derive the mechanical parameters of the carbon fiber reinforced polyetheretherketone composite material by combining the mechanical parameters of the carbon fiber;

[0009] Step 3: Use a cutting machine to cut the carbon fiber reinforced polyetheretherketone composite sheet into tensile and shear standard parts in the longitudinal and transverse directions respectively, and place them in a customized mold; perform pressure-maintaining heat treatment on the carbon fiber reinforced polyetheretherketone composite material samples in a hot press, heat them to a predetermined temperature, and then cool them to room temperature at different cooling rates; finally, measure the mechanical parameters of the carbon fiber reinforced polyetheretherketone composite material samples, compare the obtained elastic modulus, shear modulus, and Poisson's ratio with the derived values, verify the reliability, and make corrections.

[0010] Preferably, the crystallinity of polyetheretherketone when the cooling rate is ≤200°C / min is obtained by measuring its cold crystallization enthalpy, and the crystallinity of polyetheretherketone when the cooling rate is ≥300°C / min is obtained by measuring the difference between its melting enthalpy and cold crystallization enthalpy; crystallinity X c The calculation formula is as follows:

[0011]

[0012] Where wf is the volume fraction of carbon fiber, ΔH m and ΔH c are the melting enthalpy and the cold crystallization enthalpy, ΔH f The value is the melting enthalpy of polyetheretherketone when the crystallinity is 100%.

[0013] Preferably, the tensile strength R of the polyetheretherketone sample after hot pressing is m , elastic modulus E m and Poisson's ratio v m The shear modulus G is obtained based on the stress-strain curve of the tensile test of polyetheretherketone after hot pressing treatment. m , the calculation formula is:

[0014]

[0015] Where T is the maximum temperature of heat treatment and φ is the cooling rate.

[0016] Preferably, the relative crystallinity X t The relative crystallinity is calculated by the ratio of the crystallization exothermic peak area at time t in the DSC curve to the entire crystallization peak area when the crystallization is completed. The formula for calculating the relative crystallinity is:

[0017]

[0018] Where t0 is the start time of crystallization, t is the time at a certain moment, and dH / dt is the crystallization heat flow rate.

[0019] Preferably, the non-isothermal crystallization rate constant K c The calculation formula is as follows:

[0020]

[0021] Where: n is an index reflecting the dimension of the crystallization process, and the size of n is determined by the nucleation mechanism and growth mode of the crystal; K is the crystallization rate constant, K c is the crystallization rate constant of the polymer's non-isothermal crystallization process.

[0022] Preferably, the half crystallization time t 1 / 2 is the time required to reach 1 / 2 of the maximum crystallinity, t max is the time taken to reach the maximum crystallinity. The maximum crystallinity corresponds to the point where the heat flow rate dH / dt is equal to 0. The crystallization rate G is the half-crystallization time t 1 / 2 The reciprocal of is calculated as follows:

[0023]

[0024] Preferably, according to the calculation results of formula (1) and formula (2), X c 、Em 、v m , G m and σ bm Φ was plotted respectively, and a mathematical model for predicting the mechanical properties of polyetheretherketone based on processing parameters was established. m 、v m , G m and σ bm X c Draw a graph and establish a mathematical model for predicting the mechanical properties of polyetheretherketone based on crystallinity.

[0025] Preferably, the crystallinity and mechanical properties of polyetheretherketone under different processing parameters are combined, and the crystallinity and mechanical properties of carbon fiber reinforced polyetheretherketone under different processing parameters are derived according to the relationship between the mechanical parameters of the fiber and the mechanical parameters of the fiber reinforced composite material and the mechanical parameters of the matrix phase and the reinforcement phase; the obtained parameters are respectively used to calculate Φ and X c The graph was drawn, the curve was fitted, and a mathematical prediction model based on processing parameters and crystallinity was established during the non-isothermal crystallization of carbon fiber reinforced polyetheretherketone.

[0026] Preferably, multiple samples are set up under each experimental condition to ensure the reliability of the data.

[0027] The above technical features can be combined in various suitable ways or replaced by equivalent technical features, as long as the purpose of the present invention can be achieved.

[0028] The present invention provides a method for predicting mechanical parameters of composite materials, which has at least the following advantages compared with the prior art:

[0029] When analyzing the non-isothermal crystallization behavior of polyetheretherketone, it was found that there was an initial nucleation effect that was time-dependent in the crystallization process, and the nucleation mode was the coexistence of homogeneous nucleation and heterogeneous nucleation. The growth mode in the early stage of crystallization was complex, diverse, and changeable, and the proportion of heterogeneous nucleation, the growth mode of crystals, and the number of multidimensionally grown crystals were all related to the processing parameters (T and Φ). There was an obvious secondary crystallization effect in the later stage of crystallization.

[0030] Overall, X c It decreases with increasing T. Although a higher T can reduce ΔE, making it easier for crystallization to occur, a higher T intensifies the thermal motion of the PEEK molecular chain, and the intermolecular forces (van der Waals forces), electrostatic effects, and the high π-π forces between the chains gradually disappear. It becomes more difficult for the amorphous region molecular chains to develop into the orderly arranged crystalline regions, the nucleation sites are reduced, and the late growth of the crystal is insufficient. However, a lower T can keep the PEEK molecular chain arrangement relatively orderly, and while homogeneous nucleation occurs, the residual tiny crystals in the melt can be used as crystal nuclei, resulting in heterogeneous nucleation, thereby increasing the nucleation rate and crystal growth rate. cAs Φ increases, it decreases, and the rate of decline gradually decreases. Excessively rapid Φ causes the molecular chains to lag behind the cooling rate as they develop toward orderly crystal regions, shortening the crystallization time and hindering both nucleation and crystal growth. Therefore, T should be lower than the traditional 395°C setting; it is recommended to be slightly above the melting point of the material for better results and energy conservation. During non-isothermal processing, auxiliary insulation measures should be used to keep Φ within 10°C / min.

[0031] The mathematical model for predicting crystallinity and mechanical properties based on processing parameters is the Log3P1 equation in the logarithmic function model, while the mathematical model for predicting mechanical properties based on crystallinity is a quadratic equation. The accuracy of the mathematical model was verified by DSC crystallinity testing, tensile testing, and shear testing, providing a good reference and recommendation for the selection of processing parameters for polyetheretherketone and its composites. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention will be described in more detail below based on embodiments and with reference to the accompanying drawings, wherein:

[0033] Figure 1 A diagram showing the hot pressing treatment equipment and mechanical parameter testing equipment of the present invention;

[0034] Figure 2 The non-isothermal crystallization curve of PEEK is shown;

[0035] Figure 3 The non-isothermal crystallization curve of PEEK during rapid cooling is shown;

[0036] Figure 4 shows the stress-strain curve of the tensile test of PEEK after hot pressing treatment;

[0037] Figure 5 Shows the relative crystallinity X of PEEK during non-isothermal crystallization t A graph over time t;

[0038] Figure 6 The non-isothermal crystallization process of PEEK shows the lg(-ln(1-X t )) and lgt relationship diagram;

[0039] Figure 7 The relationship between lgΦ and lgt is shown;

[0040] Figure 8 A graph showing the activation energy curve for non-isothermal crystallization of PEEK is shown;

[0041] Figure 9 Shows the E of PEEK m 、v m , G m and Rm With X c relationship diagram. DETAILED DESCRIPTION

[0042] The present invention will be further described below with reference to the accompanying drawings.

[0043] The present invention provides a method for predicting the mechanical parameters of composite materials. Considering that the parameters of carbon fiber reinforced polyetheretherketone composite materials in certain directions are difficult to obtain, the mechanical parameters of carbon fiber reinforced polyetheretherketone composite materials can be derived by separately obtaining fiber parameters (by consulting literature) and resin parameters (by experimental acquisition). The derived mechanical parameters are then verified and corrected by measuring the mechanical parameters of the carbon fiber reinforced polyetheretherketone composite materials. The process for obtaining material parameters is as follows:

[0044] Step 1: Select specimen type I based on the thickness of the carbon fiber reinforced polyetheretherketone composite material and whether it is a rigid body, such as Figure 1 As shown in the figure, a water jet cutter was used to cut the polyetheretherketone sheet into tensile standard parts, which were placed in a customized stainless steel mold. According to the typical thermal history of the polyetheretherketone material during the crystallinity test, the polyetheretherketone tensile parts were subjected to pressure-maintaining heat treatment in a hot press. After being heated to a predetermined temperature, they were cooled to room temperature at different cooling rates. Three parallel samples were tested under each experimental condition to ensure the reliability of the data.

[0045] Step 2: The elastic modulus and Poisson's ratio of the polyetheretherketone sample are measured. On this basis, combined with the mechanical parameters of carbon fiber, the mechanical parameters of carbon fiber reinforced polyetheretherketone composite materials are derived.

[0046] Step 3: Referring to step 1, use a water jet cutter to cut the carbon fiber reinforced polyetheretherketone composite sheet into tensile and shear standard parts along the longitudinal direction (0°) and the transverse direction (90°), and place them in a customized stainless steel mold. Select some typical processing parameters, and perform a pressure-maintaining heat treatment on the carbon fiber reinforced polyetheretherketone composite sample in a hot press. After heating to a predetermined temperature, cool it to room temperature at different cooling rates. Finally, the mechanical parameters of the carbon fiber reinforced polyetheretherketone composite sample are measured, and the obtained elastic modulus, shear modulus, and Poisson's ratio are compared with the derived values ​​to verify reliability and make corrections.

[0047] In one embodiment, Figure 2-3 As shown, the crystallinity (X c ) can be obtained by measuring its cold crystallization enthalpy, and X c It can be obtained by measuring the difference between its melting enthalpy and cold crystallization enthalpy. c The calculation formula is as follows:

[0048] When the cooling rate is ≤200℃ / min, X c =△H c / △H f

[0049] When the cooling rate is ≥300℃ / min, X c =(ΔH m -ΔH c ) / (1-w f )△H f (1)

[0050] Where ΔH m and ΔH c are the melting enthalpy and the cold crystallization enthalpy, ΔH f The value is the melting enthalpy of polyetheretherketone when the crystallinity is 100%, that is, 130 J / g.

[0051] The tensile strength of polyetheretherketone samples after hot pressing (R m ), elastic modulus (E m ) and Poisson's ratio (v m ) can be obtained from the stress-strain curve of the tensile test of polyetheretherketone after hot pressing treatment, and the shear modulus (G m ),like Figure 4 As shown, G m The calculation formula is:

[0052]

[0053] Where T is the maximum temperature of heat treatment and φ is the cooling rate.

[0054] Under the synergistic effect of T and Φ, the crystallization peak width and T s and T p etc. have changed. s and T p Both decrease significantly with the increase of Φ (gradually move toward low temperature), and the width of the crystallization peak increases with the increase of Φ. In addition, T s and T p The influence of increases with the increase of Φ, and is most obvious when Φ is 200℃ / min. When polyetheretherketone crystallizes at a higher rate, a cold crystallization peak will appear in its melting process, and the intensity of the cold crystallization peak will continue to increase with Φ and T, while the melting peak will continue to weaken with them. The mechanical parameters of polyetheretherketone materials change with non-isothermal processing parameters, among which E m and G m The changing trend of X c Consistent, v m On the contrary. In addition, σ bmIt gradually decreases with the increase of Φ or T, and we believe that this result is caused by the change of crystallinity.

[0055] During the hole-making process of carbon fiber reinforced polyetheretherketone, due to the extraction of heat sources such as blades, the Φ of the material around the hole is generally in the rapid cooling range. When the cooling is too fast, the recrystallization behavior of the polyetheretherketone matrix around the hole is seriously affected by Φ. This may be because when Φ is too large, the molten polymer crystallizes under conditions of large supercooling, and the Gibbs free energy of the molecular chain drops sharply, resulting in the crystallization arrangement movement of the molecular chain in the amorphous region always lagging behind Φ when it develops into the orderly arranged crystalline region. In addition, a larger Φ always forces the nucleation rate and growth rate of the crystal to increase, the crystal crystallization time becomes shorter, and the acceleration of the crystallization process makes it impossible for many crystals to grow well after nucleation, which ultimately leads to X c decline.

[0056] Compared with the rapid cooling during hole making, the Φ of PEEK and its composites is in the normal cooling range during molding or 3D printing due to the presence of heat sources such as molds. We can predict that under the same T, the T of the material around the hole after hole making will be s 、T p and X c will be much smaller than the value in molding or 3D printing. c Affected by both T and Φ.

[0057] In the 3D printing process, researchers tend to use a flow temperature far higher than the melting point of the material to design the material's morphology. However, existing 3D printing parameters do not consider the effect of T on the material's crystallization behavior. As T increases, the crystallization peak curve gradually lags behind the cooling rate, and X c It gradually decreases, especially when T is 400°C. This is because the crystallization behavior of the polymer is related to the density of its own crystal nuclei before the material crystallizes. When polyetheretherketone reaches near the flow temperature (T = 400°C), the thermal motion of the internal structure of the material intensifies, and the kinetic energy and motion amplitude of the molecular chain become significantly larger. As the distance between the chains increases and rotates, the intermolecular forces (van der Waals forces), electrostatic effects, and the π-π forces with higher bond energy between chains gradually disappear, resulting in a high degree of random arrangement of the molecular chains and excessively loose stacking. In addition, the initial crystal melt is affected by high temperature, resulting in almost no tiny grains remaining. However, in the subsequent crystallization process, it takes a certain amount of time and energy to re-establish and maintain new nucleation sites inside the molecule. In other words, when T is 360°C, polyetheretherketone will have more nucleation sites when crystallizing, and homogeneous nucleation and heterogeneous nucleation can occur simultaneously. The increase in nucleation rate ultimately effectively improves the X of the material. c .

[0058] X cIt is closely related to the performance of the material. Too high T can also cause the material to suffer secondary damage, such as aging. Therefore, when performing heat treatment on the material, in order to obtain the best performance, the lower T should be adopted as much as possible.

[0059] When drilling, forming, and 3D printing polymers and their composites, it is often necessary to select the optimal process parameters based on the non-isothermal crystallization behavior of the material.

[0060] The relative crystallinity of the material (X t ) is obtained by the ratio of the crystallization exothermic peak area at time t in the DSC curve to the entire crystallization peak area when crystallization is completed. The relative crystallinity calculation formula is:

[0061]

[0062] Where t0 is the start time of crystallization, t is the time at a certain moment, and dH / dt is the crystallization heat flow rate.

[0063] like Figure 5 As shown in the figure, the relative crystallinity changes over time with a rapid change in the initial stage of crystallization, followed by a sudden decrease and slowing down in the later stages. This indicates that crystal nuclei initiate rapidly in the early stages of crystallization and grow more slowly in the later stages. Furthermore, as the cooling rate Φ increases, the crystallization process accelerates, the crystallization time decreases, and the crystallization temperature decreases.

[0064] Non-isothermal crystallization rate constant K c The calculation formula is as follows:

[0065]

[0066] Where: n is an index reflecting the dimension of the crystallization process, and the size of n is determined by the nucleation mechanism and growth mode of the crystal. K is the crystallization rate constant, K c is the crystallization rate constant of the polymer's non-isothermal crystallization process.

[0067] lg[-ln(1-X t )] Plot lgt, such as Figure 6 As shown, a linear fit was performed on the straight portion of the initial crystallization curve. During the non-isothermal crystallization of polyetheretherketone at different T and Φ conditions, except for the initial stage, which maintained a relatively good linear relationship, the curves at all other crystallization stages deviated from the original path. This indicates that during the non-isothermal crystallization process, as crystallization time progresses, the size and number of crystals gradually increase, the distance between crystals gradually decreases, and the crystals formed earlier begin to contact and collide with each other. This stage is considered the secondary growth stage of the crystal.

[0068] Half crystallization time t 1 / 2 is the time required to reach 1 / 2 of the maximum crystallinity, t maxIt is the time taken to reach the maximum crystallinity. It can be calculated that the maximum crystallinity corresponds to the point where the heat flow rate dH / dt is equal to 0, and the crystallization speed G is the half crystallization time t 1 / 2 The reciprocal of is calculated as follows:

[0069]

[0070] The non-isothermal crystallization process of polyetheretherketone has an initial nucleation effect that is time-dependent. The nucleation mode of its main crystallization process is the simultaneous existence of homogeneous nucleation and heterogeneous nucleation. The growth mode of the crystal nucleus is no longer a simple blend of crystals of different dimensions and morphologies. The change in its nucleation mode and the secondary crystallization effect are more obvious. For example, when Φ is 2℃ / min, the n1 value is close to 3, indicating that a small amount of three-dimensional spherical crystals have appeared in the early stage of crystallization. In addition, except for Φ of 150℃ / min and 200℃ / min, the n2 values ​​at other cooling rates are all greater than 3, indicating that most of the crystals develop into three-dimensional spherical crystals in the later stage of crystallization.

[0071] Overall, n1 decreases with increasing T or Φ, indicating that the nucleation mode and crystal morphology of polyetheretherketone are related to these factors. Φ, in particular, has a more significant impact. For example, at T of 360°C, n1 decreases from 2.99 to 1.54. This indicates that when Φ>25°C / min, the crystallization process is primarily homogeneous nucleation, supplemented by heterogeneous nucleation, with the growth mode consisting of one-dimensional needle-like crystals and a small amount of two-dimensional plate-like crystals. Furthermore, as Φ increases, the dominance of one-dimensional needle-like crystals becomes increasingly apparent. When Φ<25°C / min, the crystal growth mode changes significantly, with one-dimensional needle-like crystals no longer dominant and two-dimensional plate-like crystals becoming increasingly numerous. Furthermore, as Φ decreases, the two-dimensional plate-like crystals increasingly tend to evolve into three-dimensional spherical crystals.

[0072] From this we can conclude that in the early stage of non-isothermal crystallization, as Φ continues to increase, the nucleation mode of the main crystallization process of polyetheretherketone also changes accordingly (the proportion of heterogeneous nucleation gradually decreases), and the growth mode of the crystal also develops from complex and diverse crystal blends to one-dimensional needle-shaped crystals, which is exactly the X-ray diffraction of polyetheretherketone. c The main reason is that it gradually decreases as Φ increases.

[0073] In the non-isothermal crystallization process, when the cooling rate of polymer is Φ, at a certain time t and temperature T t There is a relationship between:

[0074]

[0075] Where, T t is the temperature at time t. K T It's T tThe cooling factor at temperature, m is a constant related to the crystallization nucleation mechanism and growth mode. F(T) is the cooling rate required for the polymer to reach a certain relative crystallinity per unit time, which can be expressed as F(T) = (K T / K) 1 / m ; α = n / m, where n is a constant related to the crystallization nucleation mechanism and growth mode.

[0076] Plot lgΦ against lgt, as Figure 7 As shown, with the relative crystallinity X t The F(T) increases continuously, and the F(T) increases significantly. This trend of change may be due to the fact that in the late stage of crystallization, the growth mode of the crystal gradually develops from two-dimensional crystal to three-dimensional crystal, the distance between spherulites gradually decreases, the contact between crystals intensifies, the difficulty of crystal growth becomes greater, and the crystallization behavior tends to saturate after the material reaches a high crystallization state. This further proves that the best X-ray diffraction method reported so far has been broken through. c (about 48%) is somewhat challenging.

[0077] In addition, for the entire non-isothermal crystallization process, α is always between 1.291 and 1.546, and its value increases with the t The change is slow, and generally decreases with increasing T. This indicates that heterogeneous nucleation accounts for a larger proportion of polyetheretherketone when T is low, which indirectly proves that lower T can cause some tiny grains to remain in the crystal during the melting process, allowing homogeneous nucleation and heterogeneous nucleation to occur simultaneously during the crystallization of the material.

[0078] The non-isothermal crystallization activation energy ΔE of polymer materials can be expressed as:

[0079] d[ln(Φ / T p 2 )] / d(1 / T p )=-△E / R (7)

[0080] Where T p is the peak crystallization temperature.

[0081] ln(Φ / T p 2 ) versus 1 / T p Drawing, such as Figure 8 As shown in the figure, the calculated non-isothermal crystallization activation energy ΔE values ​​of polyetheretherketone are 253.92 kJ·mol -1 , 236.54 kJ·mol -1 , 222.64 kJ·mol -1, whose value decreases with increasing T. This indicates that nucleation is more important than growth during non-isothermal crystallization. While a higher T can facilitate non-isothermal crystallization, it also creates numerous disadvantages for polymer crystallization motion and growth. Conversely, a lower T can provide a relatively favorable crystallization environment for polyetheretherketone. Therefore, when processing semi-crystalline polymers and their composites, T should be controlled near the melting point, and auxiliary thermal insulation measures should be used to keep Φ within 10°C / min.

[0082] PEEK and carbon fiber-reinforced PEEK maintained their good form after hot pressing under the protection of the mold, but the color of the PEEK gradually darkened with increasing T. In tensile and shear tests, the elongation at break of the samples gradually decreased with T and Φ, indicating that the material's elastic-plastic properties were gradually replaced by brittleness.

[0083] As Φ increases, the pore diameter and pore density on the surface of the material gradually increase, and even delamination occurs. Too high T will not only cause overheating and aging of the material, but also increase the porosity and pore diameter inside the material, making the fracture morphology very different. For samples with larger Φ, cracks appear locally in the tensile direction, indicating that as X c As the temperature decreases, the internal bonding force of the material becomes weaker and weaker, making it easier for cracks to form and then break directly.

[0084] When Φ is small, the resin distribution on the surface of carbon fiber-reinforced polyetheretherketone is relatively uniform. However, an excessively high T can cause the resin inside the material to overflow and result in localized depressions. When Φ is too large, the resin distribution on the surface becomes uneven and uneven. The tensile test fracture morphology confirms the consistency between the internal structure of the material and the surface, showing a smooth fracture, fiber pullout, and an uneven fracture caused by resin overflow and aging. By comparison, the fracture morphology of the shear test is highly consistent with the tensile test fracture morphology.

[0085] According to the calculation results of formula (1) and formula (2), X c 、E m 、v m , G m and σ bm By plotting Φ respectively, a mathematical model for predicting the mechanical properties of polyetheretherketone based on processing parameters can be established. m 、v m , G m and σ bm X c By drawing a graph, a mathematical model for predicting the mechanical properties of polyetheretherketone based on crystallinity can be established.

[0086] When Φ≤200℃ / min, X c 、E m , G m and σ bmThe decline is large, v m When Φ>200℃ / min, X c 、E m 、v m , G m and σ bm The change of Φ becomes slower and smaller with the increase of Φ. c 、E m 、v m , G m and σ bm The mathematical prediction model is:

[0087]

[0088] E m , G m and σ bm Follow X c Increases and gradually becomes larger, v m On the contrary. When polyetheretherketone is non-isothermal crystallization, the crystallinity E m 、v m , G m and σ bm The mathematical prediction model is:

[0089]

[0090] The X of polyetheretherketone under different processing parameters can be calculated by formula (8): c 、E m 、v m , G m and σ bm , different X can be calculated by formula (9) c E of PEEK m 、v m , G m and σ bm Tensile tests and DSC tests were performed on hot-pressed polyetheretherketone samples. This verification showed that the crystallinity and mechanical properties calculated using the processing parameter mathematical model have a certain degree of reliability. At the same time, mechanical property predictions based on crystallinity test values ​​or theoretical calculations also have a certain degree of reliability.

[0091] Combined with the crystallinity and mechanical properties of polyetheretherketone under different processing parameters, the crystallinity (assuming that the influence factor of fiber on the crystallinity of composite material is 1.07) and mechanical properties of carbon fiber reinforced polyetheretherketone under different processing parameters can be deduced based on the relationship between the mechanical parameters of fiber and the mechanical parameters of fiber reinforced composite materials and the mechanical parameters of matrix phase and reinforcement phase. c Drawing, such as Figure 9As shown, by fitting the curve, a mathematical prediction model based on processing parameters and crystallinity during non-isothermal crystallization of carbon fiber reinforced polyetheretherketone can be established.

[0092] X c =29.81546+0.07442×T-(-2.31083+0.02075×T)

[0093] ×ln(Φ-161.79346+0.46101×T)

[0094] E1=135.28579+0.00168×T-(-0.15358+0.0008245×T)

[0095] ×ln(Φ+94.42056-0.12861×T)

[0096] E2=E3=6.07354+0.00976×T-(-0.74063+0.00334×T)

[0097] ×ln(Φ+97.15621-0.1022×T)

[0098] v 12 =v 13 =0.20355+0.00014075×T-(-0.0118-0.00000625×T)

[0099] ×ln(Φ+20.51987-0.03215×T)

[0100] v 23 =0.23963+0.000195×T-(-0.0189-0.00003725×T)

[0101] ×ln(Φ+25.97998-0.03431×T)

[0102] G 12 =G 13 =3.7306+0.00261×T-(-0.23375+0.00126×T)

[0103] ×ln(Φ+6.14862+0.05061×T)

[0104] G 23 =2.69483+0.00269×T-(-0.21794+0.00113×T)

[0105] ×ln(Φ+43.353-0.01256×T)

[0106] σ b1 =2243.92875-0.0953×T-(5.69706-0.0026×T)

[0107] ×ln(Φ-7.55515+0.04046×T)

[0108]

[0109]

[0110] Where i and j represent different directions, i, j = 1, 2, 3. ij is the elastic modulus, G ij is the shear elastic modulus, V ij is Poisson's ratio, σ bij is the tensile strength, τ ij is the shear strength.

[0111] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely illustrative of the principles and applications of the invention. It should be understood that many modifications may be made to the illustrative embodiments, and that other arrangements may be devised, without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in ways other than those described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be employed in conjunction with other described embodiments.

Claims

1. A method for predicting mechanical parameters of composite materials, characterized in that: The following steps are involved: Step 1: Based on the thickness of the carbon fiber reinforced polyetheretherketone composite material and whether it is a rigid body, the sample type is selected. The polyetheretherketone sheet is cut into tensile standard parts using a cutting machine and placed in a customized mold. Based on the thermal history of the polyetheretherketone material during the crystallinity test, the polyetheretherketone tensile parts are subjected to pressure-maintaining heat treatment in a hot press. After heating to a predetermined temperature, they are cooled to room temperature at different cooling rates. Step 2: Measure the elastic modulus and Poisson's ratio of the polyetheretherketone sample, and derive the mechanical parameters of the carbon fiber reinforced polyetheretherketone composite material by combining the mechanical parameters of the carbon fiber; Step 3: Use a cutting machine to cut the carbon fiber reinforced polyetheretherketone composite sheet into tensile and shear standard parts in the longitudinal and transverse directions respectively, and place them in a customized mold; perform pressure-maintaining heat treatment on the carbon fiber reinforced polyetheretherketone composite sample in a hot press; finally, measure the mechanical parameters of the carbon fiber reinforced polyetheretherketone composite sample, and compare the obtained elastic modulus, shear modulus, and Poisson's ratio with the derived values ​​to verify reliability and make corrections; Tensile strength of polyetheretherketone samples after hot pressing R m , elastic modulus E m and Poisson's ratio v m The shear modulus is obtained based on the stress-strain curve of the tensile test of polyetheretherketone after hot pressing treatment and is deduced G m , the calculation formula is: （1） Where, T is the maximum temperature of heat treatment, φ is the cooling rate; Relative crystallinity X t Through the DSC curve t The relative crystallinity is calculated by the ratio of the crystallization exothermic peak area at the moment to the entire crystallization peak area when the crystallization is completed. The relative crystallinity calculation formula is: （2） In the formula t 0 is the start of crystallization time, t It's a certain moment in time. dH / dt is the crystallization heat flow rate; Non-isothermal crystallization rate constant K c The calculation formula is as follows: （3） Where: n is an index reflecting the dimension of the crystallization process. n The size of is determined by the nucleation mechanism and growth mode of the crystal; K is the crystallization rate constant, K c is the crystallization rate constant of the polymer's non-isothermal crystallization process.

2. The composite material mechanical parameter prediction method according to claim 1, characterized in that: The crystallinity of PEEK when the cooling rate is ≤200℃ / min is obtained by measuring its cold crystallization enthalpy, while the crystallinity of PEEK when the cooling rate is ≥300℃ / min is obtained by measuring the difference between its melting enthalpy and cold crystallization enthalpy; crystallinity X c The calculation formula is as follows: （4） Where w f is the volume fraction of carbon fiber, Δ H m and Δ H c are the melting enthalpy and the cold crystallization enthalpy, Δ H f The value is the melting enthalpy of polyetheretherketone when the crystallinity is 100%.

3. The composite material mechanical parameter prediction method according to claim 1, characterized in that: Half crystallization time t 1 / 2 is the time required to reach 1 / 2 of the maximum crystallinity, t max is the time taken to reach the maximum crystallinity, and the maximum crystallinity corresponding to the heat flow rate is calculated dH / dt The point where the crystallization rate is equal to 0 G Half crystallization time t 1 / 2 The reciprocal of is calculated as follows: 。 4. The composite material mechanical parameter prediction method according to claim 1, characterized in that: According to the calculation results of formula (1) and formula (2), X c 、 E m 、 v m 、G m and σ bm Respectively Φ Draw a graph and establish a mathematical model for predicting the mechanical properties of polyetheretherketone based on processing parameters. E m 、 v m 、G m and σ bm Respectively X c Draw a graph and establish a mathematical model for predicting the mechanical properties of polyetheretherketone based on crystallinity.

5. The composite material mechanical parameter prediction method according to claim 1, characterized in that: Combined with the crystallinity and mechanical properties of polyetheretherketone under different processing parameters, the crystallinity and mechanical properties of carbon fiber reinforced polyetheretherketone under different processing parameters were derived based on the relationship between the mechanical parameters of fiber and fiber reinforced composite materials and the mechanical parameters of matrix phase and reinforcement phase; the obtained parameters were respectively used to Φ and X c The graph was drawn, the curve was fitted, and a mathematical prediction model based on processing parameters and crystallinity was established during the non-isothermal crystallization of carbon fiber reinforced polyetheretherketone.

6. The composite material mechanical parameter prediction method according to claim 1, characterized in that: Multiple samples were set up under each experimental condition to ensure the reliability of the data.

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