韧性聚合物材料的基本断裂裂功和变形行为研究

用双边缺口拉伸试样研究了几种聚烯烃塑料薄片在平面应力条件下的破坏行为，从断裂功－韧带长度关系得到反映断裂韧性的材料常数比基本断裂功和反映材料塑性变形行为的比非基本断裂功，藉此分析和解释了这些材料的韧性和塑性特征，同时验算处理表明这些材料的试样断裂伸长与韧带长度均呈直线关系，线性回归相关系数达到0．97－0．99，由此求得了反映临界裂纹张开位移的材料参数等，这砦参数可用于研究材料的变形能力和断裂行为，解释材料的破坏机理。     

各有关规范防脆断措施的比较和合理性分析

本文对各有关压力容器规范防脆断措施的制订依据,沿革和修改作出分析,并对各规范中如何计及各个影响脆性断裂的主要因素作出比较,最后指出,我国规范的防脆断措施和目前对脆性断裂机理研究的进展,和国外先进规范的相应措施相比存在较大距离,以引起有关方面的的关注。     

PBX断裂力学行为研究进展

从常用实验方法、细观断裂模式、宏观断裂力学以及动态断裂方面,概述了近年来国内外关于PBX断裂力学行为的研究状况;介绍了PBX宏观和细观断裂特征及表征手段;阐述了细观结构、力学特性、温度和加载率对PBX断裂行为的影响。指出应开展PBX细观微裂纹萌生和扩展、宏观起裂机理研究,及动态加载下PBX裂纹扩展行为研究,建立适合PBX材料特性的复合型断裂准则。附参考文献51篇。     

浅谈断裂力学的发展与研究现状

本文通过对断裂力学的创立和发展的讨论,进一步说明科学技术与生产实践的进步是断裂力学产生的根本原因,继承和突破是断裂力学发展的基本途径,断裂力学的发展与生产实践紧密相关为基本论点,以及对新材料断裂理论的探索与对未来断裂力学的展望。     

韧性聚合物材料的基本断裂功和变形行为研究

用双边缺口拉伸试样研究了几种聚烯烃塑料薄片在平面应力条件下的破坏行为。从断裂功 -韧带长度关系得到反映断裂韧性的材料常数比基本断裂功和反映材料塑性变形行为的比非基本断裂功 ,藉此分析和解释了这些材料的韧性和塑性特征 ;同时验算处理表明这些材料的试样断裂伸长与韧带长度均呈直线关系 ,线性回归相关系数达到 0 97～ 0 99,由此求得了反映临界裂纹张开位移的材料参数等。这些参数可用于研究材料的变形能力和断裂行为 ,解释材料的破坏机理     

PP/POE/硅灰石复合材料性能的研究

用基本断裂功(EWF)方法研究聚丙烯(PP)/聚烯烃弹性体(POE)/硅灰石复合材料的断裂行为,研究不同硅灰石含量对复合材料断裂行为的影响,并把宏观断裂参数的变化与复合材料的微观结构联系起来,从物质结构上寻求断裂参数变化的原因.结果表明,当PP/POE/硅灰石质量比为62/8/30时,PP/POE/硅灰石复合材料的比基本断裂功为83 kJ/m2,PP/POE/硅灰石复合材料的断裂韧性主要取决于复合材料屈服后抵抗裂纹扩展的能力,PP/POE/硅灰石复合材料的塑性变形能力更依赖于屈服前的行为.相同大小的硅灰石制得的PP/POE/硅灰石复合材料的缺口冲击强度随着硅灰石含量的增加而降低.缺口冲击强度高的复合材料,比基本断裂功却较小,耐长期破裂性也较差,说明基本断裂功比缺口冲击强度更能揭示复合材料长期破坏行为的特征.     

摩尔质量分布的双峰相对高度对聚乙烯断裂及力学性能的影响

通过熔融共混商用双峰聚乙烯和单峰聚乙烯制备一系列摩尔质量分布双峰相对高度呈连续变化的双峰聚乙烯(BPE)样品,并研究了双峰相对高度对其力学性能的影响.研究表明,此系列BPE样品的双峰相对高度的变化对拉伸强度和冲击强度影响很小.但是随着BPE中低峰相对高度的增大,基本断裂功参数we大大提高,即材料抵抗裂纹开裂能力提高;而非基本断裂功参数βwp下降很小.     

全硫化超细粉末橡胶对PVC-U力学性能及形态的影响

研究了未增塑聚氯乙烯／粉末橡胶共混物的力学性能和形态特征。研究发现，随粉末橡胶用量增大，共混物的冲击强度先有所降低然后逐渐上升。实验结果和电镜图像表明：粉末橡胶基本粒子均匀分散的效果是影响共混物冲击韧性高低的重要因素；环氧化天然橡胶有促进粉末橡胶分散、改进增韧效果的作用。基本断裂功方法的研究结果表明，共混物的比基本断裂功随粉末橡胶用量增多而降低，比非基本断裂功则随之而升高，且断裂功的变化主要表现在材料屈服之前。     

PP/EPDM共混物断裂性能的研究

采用三元乙丙橡胶（EPDM）对共聚聚丙烯（PP）增韧改性。研究了共混物的力学性能和断裂性能,着重采用基本断裂功方法探讨了材料组成对共混体系断裂性能的影响。研究发现：随EPDM用量的增加,共混物的拉伸强度逐渐下降,冲击强度均较纯PP有一定程度的提高。不同组成的PP／EPDM共混物的ωe均高于纯PP,ωe值随EPDM用量的增加呈先增大后减小的趋势,且ωe主要受ωe,n变化的影响,同样βωp的变化主要受βnωp,n变化的影响。     

基于线弹性断裂力学的注塑机拉杆组件的微裂纹稳定要素的研究及应用(下)

基于线弹性断裂力学的微裂纹理论,分析了注塑机拉杆组件的微裂纹稳定要素与断裂之间的关联。纠正了传统的拉杆组件非对称循环的运动力学的特性的观点,首次提出了拉杆组件脉动循环的弹性力学的运动特性的新观点,为科学运用微裂纹稳定的应力强度因子理论奠定了理论基础。创建了微裂纹稳定的应力强度因子的判据理论,解释了拉杆断裂的力学因素,提供了卸载性能的微裂纹稳定的理论设计依据。结合实例,提出了微裂纹稳定的可靠性安全系数均值、承载能力的综合系数、脉动循环屈服强度等三个要素的工业设计理论及应用原则,提出了微裂纹稳定的卸载段直径、螺纹段底径及拉杆螺母的设计理论及确定原则。研究了线弹性断裂力学要素与弹性力学性能之间、与质量控制之间的关联,探索提高微裂纹稳定的质量要素研发方向。运用创新的拉杆组件的线弹性断裂力学要素的工业设计理论,分析了断裂失效实例,进一步说明线弹性断裂力学要素的微裂纹失稳的研究有助于预测和防止拉杆组件的断裂现象的发生。     

Studies on fracture behavior of tough PA6/PP blends

Fracture toughness of injection-molded PA6/PP blends compatibilized with SEBS-g-MA was studied using deeply double-edge notched tension (DDENT) specimens according to the essential work of fracture procedure. The fracture mechanical studies also included tensile impact tests on the DDENT specimens and characterization of the fracture surfaces by electron microscopy. The results were compared with those of traditional tensile tests and Izod impact tests on single-edge notched samples, and the sensibility of the methods was evaluated. Effects of sample position, ligament length, testing direction, and test speed were studied as well. It was found that the essential work of fracture concept, earlier applied to thin sheets, can also be applied to injection-molded tough blends. High deformation of the skin may, however, interfere with the measurements and cause a “tail” in the load-deformation curves. The plastic work of fracture (w_p) was found to correlate with the impact strength, and thus, it described the toughness. The highest values for work of fracture were recorded for the compatibilized blend with a PA6/PP ratio of 80/20. The essential work of fracture (w_e) in turn increased with increasing PA6 content and behaved like tensile strength. The test speed was found to affect the fracture behavior substantially: differences between the materials were more pronounced in high-speed tensile impact tests, which revealed signs of cavitation in addition to large-scale plastic deformation for the tough PA6-rich blend compositions. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2209–2220, 1997     

基本断裂功方法表征PP及弹性体增韧PP的冲击韧性

将基本断裂功(EWF)方法应用于聚丙烯(PP)、PP/(乙烯/丙烯/二烯)共聚物(EPDM)和PP/(乙烯/1-辛烯)共聚物(POE)共混体系的冲击韧性表征。结果表明,加入EPDM或POE后,共混物的比基本断裂功we和比塑性形变功βwp均有提高,说明弹性体的加入提高了材料抵抗裂纹扩展的能力和发生塑性形变的能力。含质量分数8%EPDM或POE的PP共混物的we和βwp高于含1%EPDM或POE的PP共混物。通过对试样冲击断面和应力发白区域的观察证实了EWF方法表征的结果。EWF方法为评价聚合物材料的断裂行为提供了更多的数据,是一种表征材料冲击韧性的极好的方法。     

Work of fracture of polystyrene/high density polyethylene blends compatibilized by triblock copolymer

The fracture toughening behavior of polystyrene/high density polyethylene blends compatibilized by 10 wt % of a styrene‐ethylene‐butylene‐styrene triblock copolymer (SEBS) was assessed using single‐edge notched tension (SENT) and double‐edge notched tension (DENT) specimens of various gauge lengths over a wide range of tensile rates. The fracture of DENT and SENT specimens was completely ductile under the plane‐stress condition. A linear relationship was observed between the specific total work of fracture and the ligament length (L) for a given L range. The results showed that the essential work (w_e) was independent of the tensile rate (R) range of 1–30 mm/min, and it then decreased considerably when R was increased to 50 mm/min and above. However, the nonessential work exhibited a rate independent trend behavior. In addition, w_e and the specific nonessential work of fracture (βw_P) were basically independent of the gauge length (G), provided that G was greater than the width of the sample. Finally, it was also shown that the w_e and βw_P values for SENT specimens are obviously greater than those for DENT specimens. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2074–2081, 2000     

Deformation mechanisms and fracture toughness of polystyrene/high‐density polyethylene blends compatibilized by triblock copolymer

A dilatometric technique was used to explore the tensile deformation mechanisms of polystyrene (PS)/high‐density polyethylene (HDPE) blends compatibilized by a styrene–ethylene–butylene–styrene (SEBS) triblock copolymer. The volume change of the sample during a uniaxial tensile process was determined with two extensometers, and it provided useful information concerning the tensile deformation mechanism. A simple model was used in this study in order to obtain quantitative information on the separate contributions of several possible deformation modes to the total deformation. The results indicated that elastic deformation was the main deformation mode for PS. However, elastic deformation was the main mode of deformation prior to yielding for SEBS compatibilized PS/HDPE blends; thereafter the plastic deformations (including shear and crazing) appeared to dominate over the elastic deformation. Moreover, crazing was the main plastic deformation mode for the blend containing 20 wt % HDPE, and shear deformation became predominant when the HDPE content was further increased. Finally, the essential work concept was used to determine the fracture toughness of the typical ductile PS/HDPE/SEBS 10/80/10 blends. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2024–2033, 2000     

Influence of carbon on stability,mechanical property,electronic structure,and lattice dynamics of silicon carbonitride

In this study, first‐principles calculations were performed to study the stability, mechanical property, electronic structure and lattice dynamics of β‐Si₃(C_x,N_1?x)₄ silicon carbonitride. The solubility of carbon in β‐Si₃(C_x,N_1?x)₄ having a stable structure is shown to be about 15 at.%. Within the limit of solubility, an increase in carbon concentration in β‐Si₃(C_x,N_1?x)₄ will lead to a decrease in the Young's modulus and density and an increase in the Poisson's ratio. The study of deformation behavior shows that the most likely slip system of is on prismatic plane rather than on basal plane. This feature of β‐Si₃(C_x,N_1?x)₄ is similar to WC. In addition, the ductility and fracture toughness of β‐Si₃(C_x,N_1?x)₄ can be optimized by controlling the carbon concentration. The improvement in ductility and fracture toughness can be attributed to the formation of metallic bonds by the incorporation of carbon atoms. The lattice dynamics study shows that the structural stability of β‐Si₃(C_x,N_1?x)₄ is controlled by energy stability criteria under stress‐free condition. In the stressed state, the structural stability of β‐Si₃(C_x,N_1?x)₄ is controlled by the elastic stability criteria. Subsequently, the β‐Si₃(C_x,N_1?x)₄ solid solution was prepared by self‐propagating high‐temperature synthesis (SHS), and the carbon‐concentration‐dependent mechanical properties were consistent with the first‐principles calculations. The maximum fracture toughness of 10.4 MPa·m^0.5 was obtained in β‐Si₃(C_x,N_1?x)₄ at carbon concentration of 5 wt%, which means that the solid solution toughening can be used as a supplement to crack bridging toughening and phase transition toughening for ceramic toughening. The results obtained in this study reveal that the β‐Si₃(C_x,N_1?x)₄ solid solution is a promising candidate for high‐speed ceramic bearings.     

温度对晶须增韧陶瓷刀具材料力学性能的影响：Ⅱ.高温断裂韧性的研究

采用表面受控裂纹法,在室温至1000℃范围内对SiC晶须增韧Al_2O_3陶瓷刀具材料JX-1的高温断裂韧性进行了测试和研究。结果表明,在低于800℃时,断裂韧性随温度变化很小,而在800℃以上断裂韧性随温度的升高而呈上升趋势。试件断口的SEM及TEM分析表明,高温下SiC晶须内部除低温存在的层错和孪晶结构外,还有大量位错的产生,并且晶须与基体的界面发生了塑性流动,。对加载速率对高温断裂韧性测试结果的影响也进行了研究。