新型碳酚醛材料动静态力学性能和本构关系研究

研究了碳纤维增强酚醛复合材料在不同温度下的动静态压缩力学性能，碳酚醛材料不但是应变率敏感材料，也是温度相关材料；提出了一个非线性粘弹性本构方程，通过对实验应力-应变曲线的拟合给出了本构方程的材料参数，讨论了温度对本构方程参数的影响；分析了材料力学行为的时温等效性，给出了不同加载条件下的时温等效曲线。     

铝合金7050-T7451高温高应变率本构方程及修正

通过分离式霍普金森压杆(SHPB)及准静态压缩实验研究铝合金7050-T7451高温高应变率下流变应力特征,利用准静态实验数据获得本构方程应变强化参数,利用SHPB实验数据获得室温下不同应变率(400～2500s-1)的应变率强化参数,以及应变率为2500s-1不同温度下(250～600℃)的热软化参数。利用不同幂次多项式对Johnson-Cook本构方程的热软化项拟合,最终选择五次多项式作为修正后本构方程热软化项。利用修正后本构方程对不同温度条件下应力-应变曲线进行预测,实验数据与预测曲线表现出良好一致性。     

形状记忆纤维热粘弹性基体复合材料的力学行为

应用热粘弹性理论和Voigt混合律,在变温场中针对马氏体逆相变过程建立了NiTi形状记忆纤维热粘弹性基体复合材料的应力-应变关系,在逆相变过程和基体呈现热粘弹态阶段,由于基体松弛其模量减小,在跃阶拉应力的作用下,复合材料的压缩应变迅速增大,纤维回复应力先增大后减小;在跃阶拉应变的作用下,复合材料的应力增加先变缓然后加快直至稳定,较高的温度和材料参数对NiTi纤维热粘弹性基体复合材料的力学行为和纤维的作动性能有明显的影响.     

NiTi纤维增强粘弹性基体与弹性基体复合材料的力学特性

借助Voigt混合律,针对马氏体逆相变过程,建立了NiTi纤维增强Kelvin粘弹性基体与弹性基体两种复合材料的应力-应变关系.在同样的升温过程及应力作用下,对两种复合材料的变形(应变)、约束态NiTi纤维逆相变开始温度进行了分析对比;升温、加载经历一段时间后,限制两种复合材料的应变为固定值,分析其受力特征.分析有助于了解NiTi纤维增强粘弹性基体与弹性基体复合材料的力学性能.     

玻纤增强聚丙烯复合材料的应变率敏感特性

采用层合热压实验法将玻璃纤维基毡与聚丙烯薄膜复合制成不同玻纤含量的玻纤增强聚丙烯(GF/PP)复合板材,在不同的加载速率下进行拉伸测试,研究GF/PP复合材料的应变率敏感特性,分析Burgers模型对该材料本构关系拟合预测的可行性。结果表明:GF/PP复合材料在低应变率范围内对应变率是敏感的,随应变率的增加,其断裂应力和抗拉强度增大;随玻璃纤维含量的增加,其所对应的应变率效应反而有所下降。同时,Burgers模型能够有效地拟合预测出该材料的拉伸应力-应变曲线,与实验曲线相比,进一步验证了GF/PP复合材料的应变率敏感特性及其变化趋势。     

平纹机织玻璃纤维增强复合材料面内压缩力学行为及破坏机制

为了研究平纹机织玻璃纤维复合材料SW200/LWR-2 的面内压缩力学性能并建立其本构模型, 对其进行了应变率为0. 001 s-1 、0. 1 s-1 、500 s-1 , 温度从- 55 ℃到100 ℃范围内的面内压缩实验研究。动态压缩实验在SHPB 装置上进行, 通过波形整形器实现了恒定应变率加载, 且经过验证试样两端应力平衡。实验结果表明, SW200/ LWR-2 复合材料性能具有明显的应变率敏感性及温度敏感性, 其强度随着应变率的升高而增大, 随着温度的升高而减小。对破坏后试样进行宏观及微观观察发现, 准静态加载时试样为剪切破坏, 伴随大量纤维束内脱粘和纤维拔出; 动态加载时试样为剪切破坏与分层破坏并存, 并出现大量碎屑, 纤维束为整束剪断, 束内脱粘受到抑制。根据损伤力学理论, 建立了SW200/ LWR-2 复合材料应变率及温度相关面内压缩损伤统计本构模型, 本构模型结果与实验结果吻合较好。      

高聚物材料动态本构关系对PP/PA共混物的应用研究

用霍布金森实验技术(SHPB)研究了两种PP/PA共混高聚物材料在高应变率(102～103s-1)下的粘弹性力学行为.实验表明,PP/PA共混高聚物材料的动态应力-应变曲线能用一个简单实用的非线性粘弹性本构方程(ZWT方程)较好地表达;通过最小二乘法拟合了材料参数;在加载过程中,理论计算值与实验结果较吻合.     

泡沫EPS非线性粘弹性本构模型在LS-DYNA空调跌落仿真中的研究

目的 研究泡沫EPS非线性粘弹性本构模型对空调跌落仿真精度的影响。方法 通过动态压缩试验获得泡沫EPS在不同应变率下的应力-应变结果,使用LS-DYNA中的非线性粘弹性本构模型Fu-Chang泡沫准确模拟泡沫在不同应变率下的力学性能,并通过空调跌落仿真进行验证。结果 使用不同应变率下的泡沫EPS非线性粘弹性本构模型进行仿真,空调不同位置的仿真加速度曲线和实际试验加速度曲线相似度在90%以上。结论 不同应变率下的泡沫EPS非线性粘弹性本构模型可以准确模拟EPS泡沫在动态冲击下的材料力学性能,可以更加准确地模拟跌落工况中空调结构的动态反应及泡沫失效状态,提高仿真精度。     

淀粉/PP基发泡缓冲包装材料动态冲击性能研究

目的 研究不同初始应变率和湿度条件下,淀粉/PP基发泡缓冲包装材料的动态冲击性能,并构建基于湿度及应变率的动态本构模型。方法 应用冲击试验机对淀粉/PP基发泡缓冲包装材料进行不同初始应变率及相对湿度下的动态冲击实验,得到其应力–应变曲线,并构建动态本构模型。结果 动态冲击下,材料的应变率效应较为明显,该材料的应力和能量吸收随着初始应变率的增加而增加。在相对湿度为50%的条件下,当应变为0.6时,随着初始应变率由30 s⁻¹分别增加至34.6、38.6 s⁻¹,材料的应力分别增加了36.1%和50.4%,能量吸收分别增加了25.8%、36.4%。该材料对环境湿度较为敏感,该材料动态冲击力学性能随着相对湿度的增加显著降低,在初始应变率为38.6 s⁻¹条件下,当应变为0.6时,随着相对湿度由50%增加到70%、90%,该材料的应力分别下降了9.7%和11.3%。另外,构建了基于初始应变率和湿度的淀粉/PP基发泡材料的动态冲击本构模型。结论 初始应变率与湿度对材料的缓冲性能有一定的影响。基于初始应变率和相对湿度的动态冲击本构模型,通过实验进行了验证,实验数据和本构模型一致性较好,该本构模型可用于预测该材料的动态冲击应力–应变曲线。     

Fe-36Ni高温高应变率动态力学性能及其本构关系

为研究Fe-36Ni因瓦合金的动态力学性能及其本构关系,在20～800℃和10-3～104 s-1的应变率内,采用电子万能试验机和高温分离式霍普金森压杆分别对Fe-36Ni因瓦合金进行准静态实验和动态压缩实验,得到其高温、高应变率下的应力-应变曲线.结果表明,Fe-36Ni因瓦合金的流动应力表现出较强的应变率和温度敏感性,随着应变率的增大而增大,随着温度的升高而减小.采用改进应变率项和温度项的Johnson-Cook本构方程拟合了Fe-36Ni因瓦合金在高温、高应变率下的动态塑性本构关系,拟合结果与试验数据吻合很好.     

Effect of flame retardants on mechanical properties,flammability and foamability of PP/wood–fiber composites

The mechanical properties, flame retardancy, thermal degradation and foaming properties of wood–fiber/PP composites have been investigated. Ammonium polyphosphate (APP) and silica were used as flame retardants. The limiting oxygen index (LOI), thermal gravimetric analysis (TGA) and cone colorimeter (CONE) were employed for the study of fire retardance. At the same time, wood–fiber/PP composite foams were produced with the batch foaming technique using CO₂ as blowing agent. The effects of APP and silica content, pressure and temperature on the final cell structure were investigated. According to LOI, TGA and cone calorimeter results obtained from the experiments, APP and silica are effective flame retardants for wood–fiber/PP composites, and silica was shown to have a flame retardant synergistic effect with APP in wood–fiber/PP composite. The mechanical properties of the composites decreased with addition of flame retardants, except for the tensile strength of small amount of silica filled wood–fiber/PP composite. The results also revealed that the cellular morphologies of the foamed wood–fiber/PP composites are a strong function of the content of APP and silica as well as foaming conditions.     

Thermo-viscoelastic modelling of organic matrix composite behaviour – Application to T700GC/M21

The purpose of this study is to propose a thermo-viscoelastic model able to describe the strain rate dependency, from creep to dynamic tests, and temperature dependency, from −100 °C to room temperature, of organic matrix composite materials. A bi-spectral viscoelastic model, proved to be representative of the T700GC/M21 behaviour on a large range of strain rates, is used and improved in this study for temperature dependency. First, thermal residual stresses are introduced and proved not to be sufficient to describe the temperature dependency of the laminate. Subsequently, further to the analysis of the time–temperature superposition principle on DMA tests, the viscoelastic model is improved with the introduction of an Arrhenius like shift factor. The proposed model is proved to be representative and predictive of the strain rate and temperature dependencies of the T700GC/M21 composite material.     

聚磷酸铵/次磷酸铝协效阻燃聚丙烯/木粉复合材料

以聚磷酸铵(APP)和次磷酸铝(AHP)为阻燃剂,马来酸酐接枝聚丙烯(MA-g-PP)为界面相容剂,通过熔融共混制备了聚丙烯(PP)/木粉(WF)复合材料。采用UL-94垂直燃烧、氧指数(LOI)、热重分析(TGA)探究了阻燃PP/WF复合材料的阻燃性和热分解过程。实验表明,当APP与AHP质量比为9∶1时,LOI值为28.3%,垂直燃烧UL-94达到V-0级。TGA和DTG测试表明,APP与AHP复配能降低木纤维的分解温度,使复合材料提前成炭,达到阻燃作用;加入APP与AHP的PP/WF复合材料的成炭率提高了141%,其高温稳定性也得到提高。通过SEM观察到,当m(APP)∶m(AHP)=9∶1时,木塑复合材料可形成致密的炭层,具有更好的隔热、隔氧作用,从而提高了阻燃性。结果表明在聚磷酸铵中加入少量的协效剂次磷酸铝可明显提高PP/WF复合材料的阻燃性。     

应力水平和纤维角度对CGF/PP复合材料蠕变行为的影响及其Burgers模型参数的数值预测

采用DMA的Creep模式分别测试了短时间内（15 min）聚丙烯（PP）在不同应力水平和温度下的单向拉伸蠕变行为,长时间内（10 h）连续玻璃纤维增强聚丙烯（CGF/PP）复合材料单层板在不同应力水平和不同纤维角度上的拉伸蠕变行为。利用Burgers黏弹性模型拟合了蠕变测试数据,构建了相关参数与应力水平和纤维角度的依赖性。结果表明:PP和CGF/PP单层板的蠕变柔量均随应力增大而显著增加,稳态蠕变速率也随之增加,蠕变模量保留率明显下降,PP基体的黏弹性主要决定了CGF/PP单层板在低应力水平下的蠕变行为; 30%应力水平下,偏轴拉伸的纤维角度在0°~90°范围内存在拉-剪耦合效应,在45°时最为显著,此时稳态蠕变速率和蠕变变形量最大;利用四元件Burgers黏弹性模型拟合各条件下蠕变曲线得到的数值模型与实验数据具有较好的相关性,相关系数达到0.99,从得到的数值模型可知相关模型参数存在明显的应力和角度依赖关系;利用模型参数的数值拟合公式分别预测10 MPa应力下0°纤维方向的蠕变曲线及45°纤维方向上30%应力水平的偏轴蠕变曲线均与实验曲线一致,表明本文得到的数值模型的可靠性。      

Coupled heat conduction and deformation in a viscoelastic composite cylinder

We study the coupled problem of deformation due to mechanical and thermal loading of a composite cylinder made up of two layers of linear isotropic viscoelastic materials. The effect of a time-varying temperature field due to unsteady heat conduction on the short term and long term material response is examined in terms of the stress, displacement, and strain fields. The material properties of the two layers of the composite cylinder at any given location and time are assumed to depend on the temperature at that location at that given instant of time. Sequentially coupled analyses of heat conduction and deformation of the viscoelastic composite cylinder are carried out. Analytical solutions for the stress, strain and displacement fields of the viscoelastic composite cylinder are obtained from the corresponding solution of the linear elasticity problem by applying the Correspondence Principle. We examine the discontinuity in the hoop stress and the radial strain at the interface of the two layers caused by mismatches in material properties, during transient heat conduction. We find that the discontinuities change over time as the mismatch in the moduli of the two layers changes due to the material properties which are time-dependent. We also investigate the effect of the thermal field on the time-dependent field variables in the composite body.     

Physical and mechanical properties of injection-molded wood powder thermoplastic composites

In the last decades, filler-reinforced thermoplastics especially natural filler-reinforced plastics have been frequently used to improve the physical and thermal properties of polymer materials in plastic industry due to their low density, fully degradable, helpful to reduce the CO₂ emission, free from health hazard and low cost. At current study, wood powder/polypropylene composites (wood/PP) with different filler contents were molded by injection molding process to investigate the effect of filler content on the physical and mechanical properties of the composites. Additionally, the comparison of physical and mechanical properties between talc/PP (which has been widely used in the automotive products) and wood/PP has been carried out based on the tensile, bending, Izod impact tests and the scanning electron microscope observation on the fracture surfaces. Results showed that the highest mechanical property of wood/PP was determined at 30?wt.% wood content. More interesting is that, at the same composite density up to 30?wt.%, the mechanical property of wood/PP was much higher than that of talc/PP. Theoretically, Nielsen equation is often used to predict the elastic modulus of filler reinforced plastics, and in this study, the predicted values were in good agreement with experimental values up to 30?wt.%, after that, they were higher to the experimental values of wood/PP composite. It is considered that is due to the discounted of the distribution and orientation of the filler in the matrix in Nielsen equation.     

A thermovisco-hyperelastic constitutive model of HTPB propellant with damage at intermediate strain rates

The uniaxial compressive tests at different temperatures (223–298 K) and strain rates (\(0.40\mbox{--}63~\mbox{s}^{-1}\)) are reported to study the properties of hydroxyl-terminated polybutadiene (HTPB) propellant at intermediate strain rates, using a new INSTRON testing machine. The experimental results indicate that the compressive properties (mechanical properties and damage) of HTPB propellant are remarkably affected by temperature and strain rate and display significant nonlinear material behaviors at large strains under all the test conditions. Continuously decreasing temperature and increasing strain rate, the characteristics of stress-strain curves and damage for HTPB propellant are more complex and are significantly different from that at room temperature or at lower strain rates. A new constitutive model was developed to describe the compressive behaviors of HTPB propellant at room temperature and intermediate strain rates by simply coupling the effect of strain rate into the conventional hyperelastic model. Based on the compressive behaviors of HTPB propellant and the nonlinear viscoelastic constitutive theories, a new thermovisco-hyperelastic constitutive model with damage was proposed to predict the stress responses of the propellant at low temperatures and intermediate strain rates. In this new model, the damage is related to the viscoelastic properties of the propellant. Meanwhile, the effect of temperature on the hyperelastic properties, viscoelastic properties and damage are all considered by the macroscopical method. The constitutive parameters in the proposed constitutive models were identified by the genetic algorithm (GA)-based optimization method. By comparing the predicted and experimental results, it can be found that the developed constitutive models can correctly describe the uniaxial compressive behaviors of HTPB propellant at intermediate strain rates and different temperatures.     

热压工艺热-化学-应力三维数值模型及有限元分析

建立了复合材料热压工艺的三维热-化学-应力耦合数学模型。该模型考虑了整个工艺周期过程中的热-化学应变、材料的黏弹性效应、各向异性及玻璃化转变温度与固化度的关系。其中热-化学模型可采用完全耦合的形式求解,而应力模型则可采用单向耦合的形式求解。对AS4/3501-6层合平板的热压工艺过程用有限元方法进行了数值模拟,得到的层合板翘曲度与实验结果相符。计算结果表明,层合板厚度减小或长度增大,都会使翘曲变形增大,而工艺压强对翘曲变形影响很小。层合板的翘曲变形随着模具与层合板热膨胀系数差距的变小而减小。       

复合材料固化相关黏弹性性能演化及残余应力分析

通过对复合材料固化度和温度相关黏弹性本构方程的分析,定义一个能综合反映固化度和温度等对复合材料黏弹性性能影响的无量纲参数De_m。当参数De_m都大于10~2时,复合材料基体处于流动状态;当参数De_m都小于10~(-2)时,复合材料为弹性状态;仅当部分参数De_m小于10~2而大于10~(-2)时,复合材料处于黏弹性状态。以AS4纤维/3501-6树脂复合材料为例,基于对其参数De_m在典型固化工艺过程中的演化,研究该复合材料黏弹性性能的发展过程,发现基于参数De_m分析得到的凝胶点时间与实验结果一致。根据复合材料黏弹性性能对残余应力发展的影响,将复合材料残余应力计算分为流动阶段和黏弹性阶段,并建立了相应的状态相关黏弹性本构模型。最后通过与原始模型预测结果的比较验证了提出的本构模型,表明本文提出的计算方法与原始黏弹性本构模型计算结果一致,但大大降低了计算所需的时间和存储空间。     

石墨烯微片/聚丙烯导热复合材料的制备与性能

通过熔融共混法制备了两种不同型号石墨烯微片（GNPs）填加的GNPs/聚丙烯（PP）导热复合材料,研究了GNPs型号（KNG180,KNG150）和含量对其导热性能、密度、结晶性能和热稳定性能的影响。结果表明,KNG180 GNPs/PP复合材料密度高于KNG150 GNPs/PP,同时KNG180对提高聚丙烯结晶度的效果优于KNG150。随着石墨烯微片含量的增加,两种复合材料导热系数均明显增大,而且KNG180填充的复合材料导热性能明显优于KNG150;当KNG180的添加量为60%（质量分数）时,GNPs/PP复合材料的导热系数从纯聚丙烯的0.087 W/（m·K）提高到1.32 W/（m·K）,提高了14倍多。石墨烯微片的加入显著提高了聚丙烯的热稳定性,当KNG180或KNG150的质量分数为10%时,聚丙烯达到最大热失重速率时的温度从345.1 ℃分别提高到374.6 ℃和397.9 ℃,但是当石墨烯微片超过一定含量时,热稳定性会下降。