聚烯烃材料的冲击拉伸特性研究

冲击拉伸韧性和冲击拉伸力为衡量高聚物材料韧性不可缺少的指标。本文就低压线型聚乙烯的冲击拉伸韧性和冲击拉伸力与材料参数如密度、分子量的关系，以及不同性能原料共混物的配比对冲击拉伸性能的影响进行了系统的研究。     

环氧沥青混凝土裂纹起裂与失稳扩展的临界特征

为了获取环氧沥青混凝土的裂纹起裂与失稳扩展临界点,重构了环氧沥青混凝土非均质(集料、砂浆和空隙)多层次(矿料级配)结构三维虚拟试件,采用离散元方法实施了单边切口小梁虚拟三点弯曲试验,借助数字摄像法捕捉了室内小梁试件表面裂纹发展情况,分析了裂缝发展过程中裂缝尖端张开位移(CTOD)和裂缝口张开位移(CMOD)之间的变化关系。研究结果表明：裂尖张开位移δ₂₅参数的使用为理解实际流入断裂带用于裂缝扩展的那部分能量开辟了一条新思路;裂缝尖端张开位移和裂缝口张开位移关系曲线的两个转折点描述了裂缝起裂和临界失稳扩展状态,环氧沥青混凝土断裂过程中裂缝的扩展经历了起裂、稳定扩展和失稳扩展3个阶段;δ₂₅-CMOD曲线分析法可以作为研究沥青混凝土材料断裂行为的辅助手段。     

聚乙烯管材抗裂纹扩展性能的评价

本文介绍了聚乙烯管材抗慢速裂纹增长和抗快速裂纹扩展评价方法的研究进展。简述了正在完善的标准方法的实验原理和实验装置，对我国在此领域的研究工作提出了建议。     

THE ROLE OF PRIOR AUSTENITE GRAINS IN FATIGUE CRACK INITIATION AND PROPAGATION IN LOW CARBON MARTENSITE

Abstract— A study has been made of the role of Prior Austenite Grains (PAG) in fatigue crack initiation and propagation in low carbon martensite. The occurrence of ferrite precipitation along prior austenite grain boundaries during rapid cooling will lead to the formation of intergranular cracking. This intergranular cracking has a close relationship with the reduction of the endurance limit for fine grained low carbon martensite.     

ANALYSIS OF CRACK INITIATION AND PROPAGATION IN FRETTING FATIGUE: THE EFFECTIVE INITIAL FLAW SIZE METHODOLOGY

Abstract— A number of fretting fatigue tests were carried out on CMV steel and INCO 718 alloys under closely controlled experimental conditions. A fracture mechanics-based lifing model was developed and the Paris Law employed to predict fatigue lives under a range of experimental conditions. An effective initial flaw size was used to describe initiation and early propagation of cracks. This approach was found to give good predictions of fatigue life of specimens for different values of bulk stress under the same fretting load.     

聚乙烯泡沫塑料物理性能的研究

研究了聚乙烯泡沫塑料的力学性能。实验表明，泡沫密度、泡沫结构以及加工的方法和条件皆成为影响聚乙烯泡沫塑料力学性能的因素。随密度升高，强度呈线性增加，开孔率提高，泡沫变大造成压缩强度下降，而泡壁变厚则能提高压缩强度。还讨论了成型的压力、温度及交联度对聚乙烯泡沫塑料力学性能的影响。     

CRACK INITIATION AND PROPAGATION BEHAVIOUR OF A HEAT-TREATED CARBON STEEL IN CORROSION FATIGUE

Abstract— When estimating fatigue damage quantitatively it is important to clarify its physical basis. In this study, rotating bending fatigue tests of a heat-treated 0.45% carbon steel were carried out in 3% NaCl solution, in order to clarify the physical basis of corrosion fatigue damage from successive observations of plastic replicas. The results show that corrosion pits are generated during the early stages of cycling, then most of them grow with further cycling until a crack is initiated from each corrosion pit. The initiation of corrosion pits from slip bands is observed only in the case when the stress range is relatively large, and in the range of stress for which slip bands are produced in air. After initiation of a crack, the crack propagates by frequent interactions and coalescence with other cracks. The growth rate of an especially small crack in NaCl solution is larger than that in air. However, the growth rate of a comparatively large crack is smaller in NaCl solution than in air.     

NOTCHED MEMBER FATIGUE LIFE PREDICTIONS COMBINING CRACK INITIATION AND PROPAGATION

Abstract Fatigue lives of notched members are considered to be divided into crack initiation and propagation phases. Apparent size effects caused by crack propagation through the strain gradient of the notch are accounted for if initiation is defined as a crack size within the local notch field. The extent of this field may be estimated from fracture mechanics analysis, with its size being of the order of one tenth of the notch radius. Plasticity effects must be properly handled in predicting crack initiation, but linear elastic analysis is generally satisfactory for handling the propagation phase.     

固化反应程度对热固性聚合物热物理性能的影响

以示差扫描量热仪（ＤＳＣ）为主要研究手段,研究了环氧封端聚芳醚酮（Ｅ－ＰＥＫ）、双酚Ａ型环氧树脂（Ｅ－４４）的玻璃化转变温度（Ｔｇ）和比热（Ｃｐ）与温度和反应程度的关系。采用基团贡献法对上述材料的Ｔｇ和Ｃｐ进行了预测,引入端基和固化剂的影响对基团贡献法进行了修正。     

玻璃纤维增强聚乙烯复合材料力学及摩擦性能的研究

本文制备了结构-性能不同的纤维增强聚乙烯基复合材料,研究了纤维含量及纤维取向对聚乙烯基复合材料力学性能和摩擦性能的影响.实验结果表明:纤维含量及取向对玻纤增强的聚乙烯基复合材料的摩擦磨损性能影响较大.沿垂直纤维方向摩擦时磨损量最少,沿平行玻纤方向摩擦时摩擦系数μ最低.玻纤含量为30%的聚乙烯基复合材料耐磨性好,摩擦系数低,综合力学性能优良,是一种有应用前景的高分子抗磨材料.     

FATIGUE CRACK INITIATION AND PROPAGATION IN A LOW-CARBON STEEL OF TWO DIFFERENT GRAIN SIZES

Rotary bending fatigue tests were carried out using both plain and notched specimens of a low-carbon steel with two different grain sizes (15 and 50 μm). The process of early crack development was observed by the replication method. The effect of grain size on crack development was studied. The main conclusions were as follows. (1) Fatigue resistance, in terms of the relative positions of the S-N curves, increases with decreasing grain size. This phenomenon is related to the number of cycles to propagate a crack to failure and the condition for the non-propagation of a fatigue crack. (2) The size of a non-propagating crack, which initiates below the fatigue limit, tends to become larger as grain size increases. (3) The difference in fatigue behaviour between small (15μm) and large (50μm) grain sized specimens is due both to a decrease in crack propagation rate and a smaller non-propagating crack limit in the finer grained material.     

聚丙烯塑料的强附着油漆物性参数及附着性能研究

研究了影响以改性乙丙梳状多元共聚为主树脂的ＰＰ强附着油漆附着百分数的３个因素是主树脂的分子量及其分布和氯化长链烷基苯与有机硅复合的表面活性剂的用量，在大量的试验基础上总结出其最佳范围分别为３×１０４～５．５×１０４、２．５～３．５和１．０％～２．５％（质量）的添加量。由此合成了附着力恒为零级，耐温变性能达到－４０℃～７０℃的ＰＰ强附着力油漆。     

LLDPE/HDPE共混体系的结晶动力学及力学性能研究

对高密度聚乙烯和线性低密度聚乙烯共混体系的结晶动力学进行了研究,由差示扫描量热仪（ＤＳＣ）测得的非等温的结晶温升曲线,分析研究共混比率对共结晶动力学参数的影响。实验发现,Ａｖｒａｍｉ指数随着共混物组成的变化而有规律地变化。同时,通过偏光显微镜以及激光小角散射等实验方法,对结晶聚合物的晶体形成形态进行观察,验证了对于全部共混组成结晶结构增长的相似性,另一方面,利用拉伸试验等手段,对共混物的力学性能进     

EVALUATION OF FATIGUE CRACK PROPAGATION PROPERTIES UNDER RANDOM LOADING AVOIDING CRACK CLOSURE

Abstract— Fatigue crack propagation rates and the fatigue threshold of HT80 steel were measured by maintaining the maximum load during the whole period of random loading in order to prevent fatigue crack closure. The random loading pattern involved 62 level block loadings in which the waveform was approximated to the Rayleigh distribution of peaks. The fatigue crack propagation rates under random loading were well predicted from those obtained from constant amplitude loading and assuming a linear cumulative damage law. That is, da/dn = C {Δ K ^m_eq−Δ K ^m_th} where the equivalent stress intensity factor, Δ K _eq={= n _iΔ K ^m_i/d n _i}^{1/ m} , where n_i = 0 for Δ K _i≤Δ K _th, or n_i = n_i for Δ K_i > Δ K _th.     

加载历史和裂纹闭合对疲劳裂纹扩展行为影响的数值模拟

采用不同应力比条件下的16MnR钢紧凑拉伸试样,设计了三种有限元分析模型,即不考虑加载历史效应的静态裂纹扩展模型,同时考虑加载历史和裂纹闭合的动态裂纹扩展模型以及仅考虑加载历史的伪动态裂纹扩展模型,对疲劳裂纹闭合过程、裂纹尖端的应力-应变迟滞环、疲劳损伤和裂纹扩展速率进行了数值模拟与分析,进而着重探讨了加载历史和裂纹闭合影响疲劳裂纹扩展行为的交互作用机制。结果表明：对于同类分析模型,应力比越大越不容易产生裂纹闭合;而在应力比相同的情况下,加载历史引起的残余压应力对裂纹闭合有明显的促进作用。裂纹闭合效应阻碍了平均应力的松弛,减小了裂纹尖端附近的应力-应变场强度、疲劳损伤和裂纹扩展速率,而加载历史引起的残余压应力则加快了平均应力的松弛和抑制了棘轮效应。与实验结果比较发现,只有同时考虑了裂纹闭合效应和加载历史影响的动态裂纹扩展模型,才能对疲劳裂纹扩展行为进行准确、定量的模拟。     

LD10铝合金疲劳裂纹扩展速率的研究

用三点弯曲多试样方法研究了LD10铝合金的疲劳裂纹扩展速率规律,从而为装备的安全可靠性提供数据依据,利用这些数据可以评估在役装备的剩余寿命。     

单相fcc金属晶内裂纹萌生与扩展的TEM原位分析

用ＴＥＭ拉伸方法,对具有ｆｃｃ结构的３０４Ｌ钢,进行了晶内裂纹萌生与裂纹志愿的原位观察,结果表明：晶内开裂时首先形成无位错区,裂纹在无位错区 形成,裂尖护 裂尖前晶面变形行为由原位观察和原位选区衍射的结果进行分析,裂纹沿（１００）晶面扩展时,裂尖前（１００）同发生倾转,（１１１）晶面局部弹性弯曲,裂尖钝化;（１００）倾声讨在以致开裂,钝化裂尖扩展,（１１１）局部弯曲有所恢复。     

理化检验试样与成品中板性能不一致的实验研究

对中板理化检验试样与中板成品力学性能的不一致性进行了分析研究。结果表明，空冷和缓冷对剪切后的理化检验试样的强度性能影响不大，但对冲击韧性和冷弯性能有较大的影响，这主要是由冷却过程中产生的质热应力所致。冷却速度快，试样产生的热应力大，导致冲击韧性及冷弯性能降低。用石棉保温冷却的方法来处理剪切下来的理化检验试样，所得性能能够真实地反映堆垛成品中板的实际力学性能。     

中心裂纹混凝土板的裂纹扩展和延迟失稳

本文把混凝土看作是具有损坏区的粘弹性材料,并结合裂纹前缘破坏过程的观测资料,提出了带裂纹的混凝土和破坏模型,研究了混凝土裂纹的早期扩展和延迟失稳问题。用本文给出的理论,较好地解释了在工程实际中所观察到的,以及大量实验所证实了的混凝土的早期裂纹扩展问题,并与实验数据符合较好。因此,对预测长期持续载荷作用下混凝土结构的安全性具有实际的意义。