汽车内饰件模外装饰用PMMA的力学性能

为研究汽车内饰件模外装饰材料聚甲基丙烯酸甲酯(PMMA)的力学性能,对PMMA膜材分别在2.5 mm/min(0.001 667 s-1),5 mm/min(0.003 333 s-1)和10 mm/min(0.006 667 s-1)不同拉伸速率下进行高温[90℃(363K),105℃(378 K)和115℃(388 K)]单向拉伸实验,得到了不同条件下的应力–应变曲线。实验结果表明,当加热温度相同时,随着应变速率的增大,PMMA的应力、延伸率和屈服应力也逐渐提升。当应变速率一致时,其屈服强度与应力随着温度的升高而逐渐变小。     

模外装饰鼠标外壳贴膜工艺仿真分析

为了研究模外装饰鼠标外壳贴膜工艺,对PMMA塑料板材进行高温单向拉伸实验,计算出DSGZ黏弹性本构模型系数,并将DSGZ模型的预测曲线与其实验数据进行对比分析。采用弹性预测-径向回映算法设计编写了DSGZ黏弹性本构模型的ABAQUS用户材料子程序,然后基于OMD工艺原理,对鼠标外壳OMD贴膜的工艺成型过程进行仿真分析,得到了成型后薄膜的厚度分布及其在X、Y方向上的变形量。     

聚丙烯树脂在高拉伸应变速率下的拉伸行为

研究了拉伸应变速率特别是高应变速率对聚丙烯树脂应力应变曲线的影响,比较了不同滑石粉添加比例和不同温度下聚丙烯树脂高速度拉伸破坏行为的差异。结果表明:聚丙烯树脂的拉伸强度随着应变速率对数的增大而线性增加;不同分子链结构的聚丙烯树脂在同一高拉伸应变速率下有不同的拉伸强度和拉伸应变;应变速率从6 s~(-1)增加到125 s~(-1)时,聚丙烯树脂拉伸强度对应变速率变化的敏感性相差不大。高应变速率下,滑石粉含量越高,拉伸强度越低;但当应变速率增加到100 s~(-1)时,不同滑石粉含量试样的拉伸断裂应变相差不大。而且,聚丙烯树脂的拉伸强度随温度升高而明显降低,断裂应变随温度的升高则有所增加;温度越低,试样的应力发白区域则逐渐变小。     

纳米碳酸钙改性聚丙烯大变形行为的研究

为了研究纳米碳酸钙改性聚丙烯(PP/nano-CaCO_3)在不同应变率下的大变形特性及相关机理,采用疲劳试验机(MTS)结合数字图像相关技术(DIC)对该种材料在不同拉伸速率下进行单项拉伸试验,并用有限元对其进行数值模拟,得出了不同变形程度的试验结果。之后采用电镜扫描(SEM)对不同变形程度的试件表面进行分析。结果表明:PP/nano-CaCO_3在不同拉伸速率下的应力-应变可分为线弹性阶段、屈服阶段、软化颈缩阶段及应力稳定阶段。其中,线弹性阶段、屈服阶段及峰值应力基本不受拉伸速率的影响,应力稳定阶段的稳定应力随着拉伸速率的增大而减小,测试试件的延展率超过300%后仍可继续拉伸延长。电镜扫描发现:随着变形量的增大,试件表面的纹理及皱褶凸起也增大。总的来说,PP/nano-CaCO_3相比纯PP具有更好的应力-应变稳定性、延展性及柔软度,在抗冲击及承载结构件中具有很好的应用前景。     

不同剪切历史和热历史对原油滞回环的影响

胶凝含蜡原油由于其蜡晶的三维网状空间结构,具有复杂的流变性。胶凝原油的流变性质一直是研究的重点和热点。通过实验,研究了在不同剪切历史和热历史作用下胶凝原油滞回环的不同变化规律。实验结果表明,对于不同的降温速率,在同一剪切条件下,当降温速率较低时,其原油屈服应力较大,滞回环曲线凸起较高,但随着剪切速率的增加,其应力逐渐接近,滞回环曲线逐渐接近;对于不同的胶凝温度,在同一剪切条件下,胶凝温度越低的,其屈服应力较大,并且随着剪切速率的增加,应力之间的差别虽变小,但胶凝温度低的比胶凝温度高的大,在滞回环曲线上可以看到低温度的曲线比高温度的曲线所对应的应力大;对于不同的剪切速率,剪切速率变化率大的,其屈服应力大,但随着剪切速率的增大,滞回环曲线相接近,即其应力也逐渐相接近。     

EPS材料的力学性能试验研究

通过室内试验,在有无侧限、不同加载速率、不同控制方式和不同围压的条件下,研究了具有密闭空腔结构的成型聚苯乙烯泡沫塑料(EPS)的力学性能.结果表明:EPS材料的应力-应变曲线可分为线弹性、塑性和硬化三个阶段;应变相同时,有侧限时应力值比无侧限时略有提高,并且随着材料密度的增大,应力值不断增大,硬化点也不断提前;相同应变下的应力值会随着加载速率的增加而不断增加;另外,在同一压应力条件下,应变控制式所获曲线的应变较应力控制式时大;在同一应变条件下,材料的应力随着围压的增大而不断减小,当材料进人硬化阶段后,材料的应力却随着围压的增大而不断增大.     

聚碳酸酯的拉伸力学行为

本文通过拉伸实验研究了国产聚碳酸酯板的力学行为,得到了这种材料在不同应变速率下的真实应力—应变曲线。实验结果表明:聚碳酸酯为应变率敏感材料,在达到峰值应力之前,泊松比接近0.5,出现颈缩之后,其泊凇比远超过极限值O.5。     

基于动态蠕变试验的沥青混合料黏弹性分析

基于沥青混合料Burgers模型的黏弹性理论,通过动态蠕变试验进行AC-20黏弹性分析,得到不同温度及应力下的混合料变形特征曲线及Burgers模型4个参数的变化规律．结果表明：在同一温度下,随应力水平增加,永久变形随之增大,稳定期永久应变发展速率增大且破坏期提前到来,Burgers模型参数中E1、E2增大,η1、η2减小;在同一应力水平下,永久变形会随温度升高而增大,同时E1、E2减小,η1,η2增大．因此应力及温度对沥青混合料黏性及弹性影响程度不同,随着应力增加,弹性增强而黏性降低;随温度升高,则弹性降低而黏性增加,该结论与路面实际使用状况一致．     

混凝土静动态轴向拉伸力学性能

为了解动荷载作用下混凝土结构响应特点,探讨轴向拉伸作用下混凝土静动态力学性能关系,通过对棱柱体混凝土试件进行轴向拉伸试验,分析了7种不同应变速率条件下混凝土试件应力--应变关系曲线、轴向拉伸强度、弹性模量、峰值应变的变化规律。结果表明:随着应变速率的不同,混凝土试件破坏形态发生了变化;混凝土动态轴向拉伸强度、弹性模量和峰值应变均随着应变速率的增加而逐渐增大;混凝土动态轴向拉伸强度、弹性模量和峰值应变增长因子同动静态应变速率比值的对数呈线性增长关系。     

基于微裂纹统计模型的PBX力学行为

将微分形式的Visco-SCRAM模型简化为单轴应力下的增量形式,用其拟合出PBX在不同应变率的单轴拉伸与单轴压缩下的应力应变曲线,然后根据微裂纹平均半径的变化分析其相应的细观物理过程,并分析了黏性对PBX力学性能的影响.结果表明,Visco-SCRAM模型能反映PBX强度与模量的拉压不对称性和应变率效应.破坏时的微裂纹平均半径随应变率的增大而增大,且该值在拉伸加载下明显小于压缩的情况.在一定范围内,随着黏性的减小,模量和强度增大,而破坏应变减小.     

Thermal and strain rate sensitive compressive behavior of polycarbonate polymer - experimental and constitutive analysis

The mechanical behavior of polycarbonate (PC) polymer was investigated under the effect of various temperatures and strain rates. Characterization of polymer was carried out through uniaxial compression tests and split Hopkinson pressure bar (SHPB) dynamic tests for low and high strain rates respectively. The experiments were performed for strain rates varying from 10 ^?3 to 10³ and temperature range of 213 to 393 K. By conducting these experiments, the true stress–strain (SS) curves were obtained at different temperatures and strain rates. The results from experiments reveal that the stress–strain behavior of polycarbonates is different at lower and higher strain rates. At higher strain rate, the polymer yields at higher yield stress compared to that at low strain rate. At lower strain rate, the yield stress of the polymer increases with the increase in strain rate while it decreases significantly with the increase of temperature. Likewise, initial elastic modulus, yield and flow stress increase with the increase in strain rate while decreases with the increase in temperature. The yield stress increases significantly for low temperature and higher strain rates. On the basis of experimental findings, a phenomenological constitutive model was employed to capture the mechanical behavior of polymer under temperature and loading rate variations. The model predicted the yield stress of polymer at varying strain rate and temperature also it successfully predicted the compressive behavior of polymer under entire range of deformation.     

A formulation of the cooperative model for the yield stress of amorphous polymers for a wide range of strain rates and temperatures

The mechanical response of solid amorphous polymers is strongly dependent on the temperature and strain rate. More specifically, the yield stress increases dramatically for the low temperatures as well as for the high strain rates. To describe this behavior, we propose a new formulation of the cooperative model of Fotheringham and Cherry where the final mathematical form of the model is derived according to the strain rate/temperature superposition principle of the yield stress. According to our development, the yield behavior can be correlated to the secondary relaxation and we propose an extension of the model to temperatures above the glass transition temperature. For a wide range of temperatures and strain rates (including the impact strain rates), the predicted compressive yield stresses obtained for the polycarbonate (PC) and the polymethylmethacrylate (PMMA) are in excellent agreement with the experimental data found in the literature.     

Impact behavior and modeling of engineering polymers

Because of their many unique and desirable properties, engineering polymers have increasingly been applied in applications where impact behavior is of primary concern. In this paper, the impact behavior of a glassy polymer acrylonitrile‐butadiene‐styrene (ABS) and a semicrystalline polymer alloy of polycarbonate and polybutylene‐terephthalates (PBT) are obtained as a function of impact velocity and temperature from the standard ASTM D3763 multiaxial impact test. As computer simulation of destructive impact events requires two material models, a constitutive model and a failure model, uniaxial mechanical tests of the two polymers are carried out to obtain true stress vs, true strain curves at various temperatures and strain rates. The generalized DSGZ constitutive model, previously developed by the authors to uniformly describe the entire range of deformation behavior of glassy and semicrystalline polymers for any monotonic loading modes, is calibrated and applied. The thermomechanical coupling phenomenon of polymers during high strain rate plastic deformation is considered and modeled. A failure criterion based on maximum plastic strain is proposed. Finally, the generalized DSGZ model, the thermomechanical coupling model, and the failure criterion are integrated into the commercial finite element analysis package ABAQUS/Explicit through a user material subroutine to simulate the multiaxial impact behavior of the two polymers ABS and PBT. Impact load vs. striker displacement curves and impact energy vs. striker displacement curves from computer simulation are compared with multiaxial impact test data and were found to be in good agreement.     

Effect of Acrylonitrile-Butadiene-Styrene High-Rubber Powder and Strain Rate on the Morphology and Mechanical Properties of Acrylonitrile-Butadiene-Styrene/Poly (Methyl Methacrylate) Blends

Acrylonitrile-butadiene-styrene (ABS) high-rubber powder (HRP) toughened acrylonitrile-butadiene-styrene (ABS)/polymethyl methacrylate (PMMA) blends were prepared in a co-rotating twin screw extruder. The effect of ABS HRP on mechanical and morphology properties of ABS/PMMA blends was studied. It is shown that the toughness of ABS/PMMA blends was improved effectively with the incorporation of ABS HRP, while the elastic modulus and tensile strength decrease slightly. Tensile tests at different strain rates were carried out in order to investigate the influence of strain rate on mechanical properties of various blends. Finally, the strain rate sensitive behavior of different blends was explored by using the Eyring model.     

Tensile mechanical properties and constitutive model for HTPB propellant at low temperature and high strain rate

To investigate the mechanical properties and fracture mechanisms of hydroxyl‐terminated polybutadiene (HTPB) propellant at low temperature and high strain rate, uniaxial tensile tests were conducted over the range of temperatures 233 to 298 K and strain rates 0.4 to 14.14 s^?1 using an INSTRON testing machine, and scanning electron microscope (SEM) was employed to observe the tensile fracture surfaces. The experimental results indicate that the deformation properties of HTPB propellant are remarkably influenced by temperature and strain rate. The characteristics of stress–strain curves at low temperatures are different from that at room temperature, and the effects of temperature and strain rate on the mechanical properties are closely related to the changes of properties and the fracture mechanisms of HTPB propellant. The dominating fracture mechanism depends much on the temperature and changes from the dewetting and matrix tearing at room temperature to the particle brittle fracture at low temperature, and the effect of strain rate only alters the mechanism in a quantitative manner. Finally, a nonlinear viscoelastic constitutive model incorporating the damage evolution and the effects of temperature and strain rate was developed to describe the stress responses of this propellant under the test conditions. During this process, the Schapery‐type constitutive theories were applied and one damage variable was considered to establish the damage evolution function. The overlap between experimental results and predicted results are generally good, which confirms that the developed constitutive model is valid, however, further researches should be done due to some drawbacks in describing the deformation behaviors at very large strain. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42104.     

Tensile yield parameters for poly(vinylchloride) blends with a methyl methacrylate–butadiene–styrene impact modifier

Tensile yield measurements were made on blends of poly(vinyl chloride) (PVC) with a methyl methacrylate-butadiene-styrene impact modifier (MBS) covering a blend range of 0 to 20 wt % MBS, a temperature range of ?50 to 25°C, and a strain rate range of 10^?3 to 10° s^?1. Increasing MBS level in PVC reduces the tensile yield stress. The tensile yield stress variation with temperature and strain rate at constant MBS level was represented in terms of the Ree-Eyring-Roetling rate model. This model represents the experimental data within experimental error. The tensile yield parameters were also determined by assuming that stress concentrations exist around the modifier equatorial plane. Estimates of these stress concentrations were made and are discussed in terms of Goodier's model for spherical inclusions.     

Analytical and experimental study of the die drawing of circular rods through conical dies

An analysis is presented of the process of die drawing isotropic polymers, in the form of circular rods, to produce highly oriented materials with enhanced mechanical properties. The stresses in a small element of material undergoing the drawing process have been analyzed using a force-equilibrium approach and the initial yield and flow stresses in the material have been predicted from the von-Mises yield criterion. The stress-strain-strain rate characteristics of the polymer used in the analysis were deduced from uniaxial tensile test data obtained at the same temperature at which the die drawing occurred. Experimental results are presented of the stress in polypropylene GSE-108 rods when die drawn at 90°C in a purpose-built die drawing facility. Novel techniques were used to determine the stress and strain distributions along the die. A comparison of the experimental results and the analytical predictions shows good agreement.     

Stress-strain behavior of styrene-acrylonitrile/glass bead composites in the glassy region

The effects of temperature, strain rate and filler content on tensile properties of SAN/glass bead composites are studied. A point of discontinuity on the stress-strain curves for unannealed composites is investigated, annealing results in smooth curves with no discontinuities. A simple model for the filler effect on yield stress is suggested and shown to be in a good agreement with experimental data. A double shifting procedure to account for the temperature and filler effects on yield stress as a function of strain rate is proposed. A single master curve that can be represented by the equation: relates composite yield stress to strain rate, temperature and filler volume fraction.     

HTPB推进剂的低温力学性能

通过低温和低温恢复常温单轴拉伸试验,考察了低温条件下HTPB推进剂力学性能的变化情况,用SEM扫描电镜观察了推进剂拉伸断面形貌,分析了所得HTPB推进剂的拉伸应力-应变曲线和力学性能特性。结果表明,在低温拉伸条件下,HTPB推进剂主要表现为基体撕裂和颗粒脆断,而在低温恢复常温拉伸条件下,主要以"脱湿"破坏为主。推进剂的低温拉伸曲线具有明显的屈服现象发生,说明推进剂的屈服现象与低温有关。推进剂在低温和低温恢复常温条件下的最大抗拉强度、弹性模量和延伸率等力学性能呈现出不同的变化规律。