Crack closure in fibre metal laminates

GLARE is a fibre metal laminate (FML) built up of alternating layers of S2-glass/FM94 prepreg and aluminium 2024-T3. The excellent fatigue behaviour of GLARE can be described with a recently published analytical prediction model. This model is based on linear elastic fracture mechanics and the assumption that a similar stress state in the aluminium layers of GLARE and monolithic aluminium result in the same crack growth behaviour. It therefore describes the crack growth with an effective stress intensity factor (SIF) range at the crack tip in the aluminium layers, including the effect of internal residual stress as result of curing and the stiffness differences between the individual layers. In that model, an empirical relation is used to calculate the effective SIF range, which had been determined without sufficiently investigating the effect of crack closure. This paper presents the research performed on crack closure in GLARE. It is assumed that crack closure in FMLs is determined by the actual stress cycles in the metal layers and that it can be described with the available relations for monolithic aluminium published in the literature. Fatigue crack growth experiments have been performed on GLARE specimens in which crack growth rates and crack opening stresses have been recorded. The prediction model incorporating the crack closure relation for aluminium 2024-T3 obtained from the literature has been validated with the test results. It is concluded that crack growth in GLARE can be correlated with the effective SIF range at the crack tip in the aluminium layers, if it is determined with the crack closure relation for aluminium 2024-T3 based on actual stresses in the aluminium layers.     

S-N-P curves in 7075 T7351 and 2024 T3 aluminium alloys subjected to surface treatments

The S-N-P (stress, number of cycles, failure probability) curves for 2024 T3 and 7075 T7351 aluminium alloys were obtained. Previously, surface treatments of degreasing and different types of anodizing were applied to samples, evaluating the influence of these treatments on the fatigue life of the alloys. The determination of the S-N-P curves was done using Maennig's method. Rotary fatigue was used because this technique produces greater stress on the sample surfaces, the zone in which it is important to evaluate fatigue resistance. Both the transition range and the finite life range were evaluated, calculating the 1, 50 and 99% fracture probability. SEM was performed in order to characterize the fracture micromechanism. The conclusions were that Maennig's method is useful to evaluate fatigue life of these materials in a fast and efficient manner. Moreover, surface treatments produce a decrease in the fatigue life of both alloys, associating this effect with the surface damage produced on each sample during the treatment.     

Finite-element analysis and experimental study on tensile fatigue behaviour of bitumen–stone adhesion

Tensile fatigue behaviours of bitumen–stone adhesion were investigated using a dynamic mechanics analyser under stress‐controlled mode at two temperatures of 5 and 25°C and various controlled‐stress levels. Failure characteristics including interfacial failure and cohesive failure were examined using image analysis of fracture surfaces. Finite‐element analysis on stress distributions was conducted under different temperatures, film thickness and interfacial bonding conditions. A Coulomb–Mohr like criterion in combination with shear and normal stresses is proposed to deal with the extreme thin adhesive layer, which can be further simplified into an adhesive zone without significant loss of accuracy for stress analysis.     

改进的基于TMS320DM642的疲劳检测系统

针对疲劳检测算法中大数据量、高速传输、复杂运算的实际需要，设计了以SAA7115为视频采集A／D、DSPTMS320DM642为核心处理器、SAA7105为视频输出D／A，并以FPGA控制输出来实现增强显示功能的实时视频处理系统。该系统采用双摄像头控制采集数据，可以满足多路视频的实时采集、处理、显示需求，可以作为疲劳检测算法、视频处理和图像处理的硬件平台。     

CFRP强度复合Weibull分布的物理特征分析

本文对ＣＦＲＰ材料疲劳后剩余强度的复合Ｗｅｉｂｕｌｌ分布的物理特征进行了初步分析。指出树脂基复合材料失效（破坏）机理的双重性（基体和纤维失效模型）决定了剩余强度（累积损伤程度）测试结果的分布特征。复合Ｗｅｉｂｕｌｌ分布曲线的特征与分析结果对设计、使用及材料研究都有重要参考意义。     

链烷烃的表面张力与内压

对Ｄａｖｉｓ和Ｒｏｓｓｅｉｎｓｋｙ提出的关系检验表明，液体的表面张力σ与Ｐ１Ｖｍ１／３之比不仅取决于温度，还与液体的种类有关，据此，建立了一个能由链烷烃的分子结构准确预测其表面张力的方法。     

LZW压缩算法解析及应用设计

ＬＺＷ压缩算法是一种无限压缩算法，它主要是用一种代码来表示数据流中出现的重复串，以达到压缩的目的。     

Corrosion fatigue short crack growth behaviour in a high strength steel

The influence of an aggressive environment (0.6 M, aerated NaCl solution) on short fatigue crack initiation and growth behaviour has been studied. The study involved three major test series, namely: air fatigue, corrosion fatigue, and intermittent air fatigue/corrosion fatigue. The above tests carried out under fully reversed torsional loading conditions at a frequency of 5 Hz, showed that it was the non-metallic inclusions which took part in crack initiation resulting from debonding at metal matrix/inclusion interface and pitting of inclusions in both air and corrosove environments, respectively. Short fatigue crack growth results in these two environments obtained by using plastic replication technique, indicated a large effect of microstructure i.e. prior austenite grain boundaries. The stage/stages at which the environmental contribution was dominant has been discussed by considering the results achieved from intermittent tests. However, the mechanisms involved in corrosion fatigue short crack growth have also been described in the light of results obtained from futher investigations carried out by conducting corrosion fatigue tests under applied cathodic potential conditions and tests on hydrogen pre-charged specimens under air fatigue and uniaxial tension conditions.     

低合金高强度钢的微观组织和疲劳裂纹扩展行为

用透射电镜观察了３０ＣｒＭｎＳｉＮｉ２Ａ钢等温的微观组织，疲劳裂纹扩展行为、裂纹尖端塑性区和位错结构，结果表明，等温状态组织由马氏体和贝氏体组成。在一个奥氏体晶粒内一般存在四个板条领域、裂纹尖端的塑性区内存在主位错带，疲劳断裂的基本组织单元为板条晶或板条束。裂纹遇到板条束界时方向发生较大偏斜。     

Effect of phase transfer catalysts on the interfacial tension of water/toluene system

The effect on the interfacial tension of the water toluene system has been studied at 25 °C in the presence of four phase-transfer catalysts i.e. tricaprylmethyl ammonium chloride, hexadecyltrimethyl ammonium chloride, hex-adecytrimethyl ammonium bromide and hexadecyltributyl phosphonium bromide. The interfacial tension of aqueous phenol/resorcinol-toluene in the presence and absence of tricaprylmethyl ammonium chloride has also been reported. Attempt has been made to elucidate the change in volumetric rate of extraction with different catalysts for two phase reactions, on the basis of interfacial tension.