几种尼龙断裂韧性的研究

用J积分方法测定了尼龙-66、尼龙-1010、尼龙-610等工程塑料的断裂韧性並用J1c来表征。本文还对J积分的原理进行了简单的阐述。     

三元乙丙橡胶增韧聚丙烯的断裂韧性研究

用三点弯曲方法测定三元乙丙橡胶增韧聚丙烯材料在-20℃和22℃时的断裂韧性,用与起裂点相应的J积分临界值J_(lc)来表示,其值分别为3.2kJ/m~2和4.6kJ/m~2。实验发现在低温和常温时试样都出现颈缩现象,说明该材料裂尖处存在着较大的塑性区,但表现一定的脆性。试验结果表明,用J积分方法测定本材料的断裂韧性、建立相应的材料断裂判据是可行的。     

基于边界元法求解二维Ⅰ-Ⅱ复合型裂纹断裂参数

对于平面复合型裂纹,由于不同的断裂模式,1J积分与应力强度因子有关。因此,必须另外分析如何分离应力强度因子。2J积分结合1J积分或应变能释放率(SERR),可以用于有效的离散和计算应力强度因子。本文介绍III?复合型裂纹的1J,2J的计算,展示了两个各向同性和均质材料属性的示例,在不同裂纹形状和荷载条件情况下,得到了应力强度因子和1J,2J的相应积分值。     

表征聚合物材料韧性的一种新方法：J积分法

介绍了J积分的概念及其理论,并运用该理论建立了一套较为完整的测试方法。对PVC和PVC/ABS共混物的测试结果表明,该方法可行,临界断裂韧性(J_(IC)值符合一般规律。     

强度组配对含有横向裂纹焊接接头J积分的影响

以含有横向裂纹的焊接接头为研究对象 ,采用有限元软件ANSYS计算了平面应力条件下几种焊缝强度组配和焊缝宽度在不同载荷下的J积分值。计算结果表明 ,对于含有横向裂纹的焊接接头 ,在线弹性和小屈服范围内 ,即P/P0 <1,强度组配对J积分几乎没有影响 ;在弹塑性范围内 ,即P/P0 >1,强度组配对J积分的影响与a/h有关。随着a/h的增大 ,强度组配对J积分构成影响所需要的载荷越来越大。当裂纹尺寸很小且载荷程度P/P0 >0 .9时 ,焊缝宽度对J积分有明显的影响 ;当裂纹尺寸大于焊缝宽度很多后 ,焊缝宽度对J积分的影响消失     

20g钢在高温下的断裂行为

对20g钢的高温断裂行为进行了试验研究：高温断裂韧性的温度和应变速率效应;裂纹扩展速率da／dt与C*积分的相关性。试验结果表明,断裂韧性Ji值随应变速率的增大而有较大幅度的降低;在同一应变速率下,温度400℃时的Ji值小于500℃时的。在C*=10-4～10-1J/mm2·min的负我强度下,da／dt与C*积分相关;C*积分可作为裂纹扩展速率的控制参量。温度400℃下裂纹扩展速率da／dt明显地大于500℃下的da／dt。因此,在温度400℃左右时更应尽量避免超载。     

用基本断裂功表征聚合物的韧性

基本断裂功 (EWF)是一种新型的高分子材料断裂韧性的评价方法 ,它与通常使用的应力强度因子、应变能量释放速率及J -积分相比 ,具有显著的优点 ,因此逐渐受到高分子材料研究领域的广泛重视。简要介绍了EWF方法的理论背景和计算方法 ,同时还讨论了影响EWF参数的因素     

聚烯烃材料的断裂韧性研究

分析了表征断裂韧性的Ｃｈａｒｐｙ冲击实验和Ｊ积分实验方法,并且用这两种方法表征了几类聚烯烃材料的断裂韧性,讨论了材料的成型工艺、熔体流动速率（ＭＦＲ）、密度等对断裂韧性的影响。     

聚醚酰亚胺对共聚双马树脂的增韧作用

采用聚醚酰亚胺(PEI)来提高共聚双马树脂的断裂韧性。实验结果表明,PEI是共聚双马树脂的有效增韧剂;分别加入10份和12.5份的PEI,可使共聚双马树脂的断裂韧性(GIC)分别提高到650J/m2和805J/m2,弯曲模量变化不大,弯曲强度则小幅度下降。用扫描电子显微镜(SEM)和动态力学分析(DMA)研究了改性树脂体系的微观结构,发现其断裂韧性主要与相态结构有关。     

不同泊松比复合材料层板应力强度因子的计算和断裂韧性

本文比较了两组具有不同平面泊松比的玻璃纤维／环氧树脂复合材料层板的断裂韧性和缺口断裂强度，发现低泊松比复合材料层板具有较高的断裂韧性和缺口断裂强度。并用复变函数－变分方法计算了不同的泊松比材料的应力强度因子，重点研究了应力强度因子与断裂韧性的关系。     

Zähigkeit und Relaxationsverhalten von Polymethylmethacrylat,Polystyrol und Polycarbonat

For innovative applications of plastics, which take advantage of special properties of polymeric materials, comprehensive understanding on strengthening and toughening mechanisms is required. The temperature-dependent mechanical behaviour of PMMA, PS and PC under dynamic loading conditions were investigated by means of an instrumented Charpy impact tester. The elastic-plastic fracture mechanics parameters, the energy-determined J-integral, and the deformation-determined crack opening displacement, δ, enable to do structure-related quantification of micromechanical processes. The J-integral values showed a maximum, resulting from an energy-dissipative process. The maximum values for PMMA occurred at 50°C and for PC at 40°C , which is related to the secondary(β) relaxation as evaluated from the frequency dependence of the mechanical loss factor. The 0-relaxation initiated shear deformation mechanisms, which led to a local increase of toughness. In polycarbonate, toughness is strongly increased due to a stress-induced shear flow process at temperatures higher than ?25°C. Correlations between morphology and toughness can be derived with the help of optical investigations of stable crack propagation on fracture surfaces.     

A micro/macro approach to fracture in composites

The results of an integrated microscopic/macroscopic finite element analysis of fracture in fiber-reinforced composites are presented. A macroscopic analysis of a composite double-cantilever-beam (DCB) fracture toughness test specimen was carried out using a singular finite element method. The effects of fiber layup angle on strain energy release rate are discussed. Results from this analysis were input as boundary conditions to a microscopic model used to calculate J-integral values in the crack tip region. Nonhomogeneity in this region causes the elastic strain energy release rate to vary with crack tip location and geometry. Elastic-plastic calculations showed that significant matrix plasticity occurs near fibers away from the crack tip region. The constitutive equation chosen for the matrix plasticity was shown to have an important effect on the J-integral value. The results show how the microscopic J-integral is related to the macroscopic strain energy release rate.     

应力腐蚀下玻璃钢断裂韧性的实验研究

在应力腐蚀和非应力腐蚀实验条件下利用三点弯曲法测定玻璃钢断裂韧性,通过对比实验研究应力腐蚀对玻璃钢断裂韧性的影响。结果表明：在应力腐蚀下玻璃钢的断裂韧性降低,试件的厚度、初始裂纹深度与试件厚度的比值、玻璃钢的破坏形式对应力腐蚀下玻璃钢的断裂韧性均有影响。     

核壳粒子增韧工程塑料

讨论了具有橡胶核-硬塑料壳的核壳型冲击改性剂对工程塑料的增韧作用。应用多种橡胶增韧机理解释核壳粒子增韧工程塑料的原理,并比较详细地介绍了国内外采用核壳粒子增韧各类工程塑料的研究进展。     

Fracture toughness characterizations of compatibilized polyamide-6 (PA6)/poly(phenylene ether) (PPE) blends

Under the plane-strain condition, the material properties, K_IC and G_IC, of the blends, brittle or with small-scale yielding, increase with increasing elastomer content. To evaluate the critical J-integral for the ductile blends, several methods have been compared to understand the influence of elastomer content and different thicknesses using single-edge notch-bend specimens. For a given thickness, the fracture toughness increases with increasing elastomer content. Moveover, the slope of the R-curve becomes gradually steeper with increasing elastomer content and decreasing specimen thickness. J_IC values determined from ASTM E813-89 and modified ASTM E813-81 methods always give the highest and the lowest values, respectively. J_IC values determined from three other methods are comparable and can be employed to characterize the fracture toughness of the compatibilized PA6/PPE blends. It is noted that J_IC values determined from the modified ASTM E813-89 and the hysteresis energy methods are apparently independent of thickness. Therefore, these two methods may be considered as potential alternative techniques to evaluate the critical J-integral for toughened polymer blends.     

非弹性体增韧聚丙烯的研究进展

本文介绍了非弹性体增韧和弹性体与非弹性体结合增韧聚丙烯的两种改性手段,指出非弹性体增韧作为一种新的增韧方法,有可能成为制备高强度高韧性工程塑料的一种新途径.     

POE在塑料增韧改性中的应用进展

聚烯烃弹性体(POE)综合性能优异,广泛应用于通用塑料和工程塑料的增韧和抗低温改性中。与传统增韧改性剂相比,POE和功能化的POE在较低含量下就能实现材料的脆—韧转变。综述了POE和功能化SPOE对通用塑料和工程塑料改性的研究概况和应用发展。     

纳米无机粒子在塑料高性能化改性中的应用

综述了纳米无机粒子在塑料高韧性、高强度、高断裂伸长率、高耐热、高介电性及抗菌性、导电性、阻燃性、耐磨性等改性方面的应用进展。总结并讨论了纳米无机粒子的表面改性及分散处理对纳米无机粒子塑料复合材料性能的影响。     

Effect of fiber orientation on Mode I fracture toughness of CFRP

The effect of fiber orientations on fracture toughness of carbon fiber reinforced plastics (CFRP) in Mode I loading was investigated using double cantilever beam (DCB) specimens, based on mesoscopic mechanics. Mesoscopic interlaminar fracture toughness of 0//0 interphase of CFRP was evaluated with mesoscopic finite element models using experimental data. The fracture surface roughness was observed by confocal laser scanning microscopy. Then the mesoscopic interlaminar fracture toughness of CFRP was correlated with the fracture surface roughness. Additionally, the change of the Mode I macroscopic fracture toughness of CFRP was experimentally measured with changing the numbers of 0 and ±θ layers of DCB specimens. The correlation between the fracture toughness of 0//0 and θ//?θ interphases was discussed and a novel procedure was proposed to predict the macroscopic fracture toughness of θ//?θ interphase using finite element method (FEM). The fracture toughness of θ//?θ interphase analyzed by FEM was finally compared with the experimental results to verify the proposed prediction procedure. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010