双轴载荷作用下表面裂纹宏观疲劳断口形貌

报告了在不同的双轴载荷比和不同的裂纹倾斜角的情况下,表面裂纹疲劳试验的某些试验结果,并首次从裂纹扩展驱动力的角度,揭示了裂纹宏观疲劳断口的变化规律。     

模拟压力容器接管的新型十字试板的角裂纹疲劳扩展性能

用新型十字试板进行了双轴载荷下的角裂纹疲劳扩展性能的研究,以模拟压力容器接管处角裂纹的疲劳扩展行为。试板角裂纹尖端的应力强度因子采用三维边界元法计算,裂纹疲劳扩展的形貌变化采用降载勾线法记录。试验结果表明,裂纹疲劳扩展规律与双向载荷比及裂纹初始形状有关,裂纹沿长度方向的扩展速率可以用 Paris 公式表示,但在深度方向则不然。     

双向载荷条件下Ⅰ型裂纹的疲劳扩展

研究了双轴向应力状态下Ⅰ型穿透裂纹的疲劳扩展规律，采用构形合理且经精确标定应力强度因子值的双向十字形试样，在电液伺服双轴向疲劳试验机上对低合金钢（１６ＭｎＲ）进行了多种载荷比的疲劳裂纹扩展速率试验，得到了双轴向应力状态下的Ｐａｒｉｓ方程，为目前按缺陷评定规范依据单轴向疲劳试验所得数据对工程构件进行疲劳评定提供参考数据，并就当前研究者们对于双向应力场中横向载荷对疲劳裂纹扩展行为的影响的不同看法进行分析探讨。     

横向载荷对含表面裂纹对焊接头疲劳裂纹扩展速率影响的研究

研究了双向载荷作用下对焊接头表面裂纹的疲劳扩展规律。采用经精确标定应力强度因子幅值的双向十字形试样,在电液伺服双轴向疲劳试验机上对母材分别为16MnR 和 Q235-B 这两种钢的对焊试板进行了疲劳裂纹扩展试验。同时,将其结果分别与单向应力下对焊接头及母材的疲劳扩展速率进行了比较,为制定我国在役压力容器缺陷评定规范提供了参考数据。     

最大荷载对硬质聚氯乙烯疲劳裂纹扩展的影响

为研究相同应力比下最大疲劳荷载对硬质聚氯乙烯（UPVC）疲劳裂纹扩展的影响，开展了单边缺口三点弯曲SE(B)试件Ⅰ型疲劳裂纹扩展试验，基于Paris公式绘制了疲劳裂纹扩展速率曲线，对试件断口微观形貌进行对比分析。结果表明：在不同荷载条件下，随着最大荷载降低，UPVC疲劳寿命增加；UPVC疲劳断裂过程符合次级断裂模式，最大荷载越大，断口微孔洞、纤维拉丝越明显。     

有机玻璃YB-DM-11的疲劳裂纹扩展特性研究

研究了试样类型、应力比对有机玻璃YB-DM-11疲劳裂纹扩展速率、疲劳裂纹扩展平均寿命的影响。结果表明：试样类型对有机玻璃疲劳裂纹扩展速率影响很小,但紧凑拉伸试样的寿命大于中心裂纹拉伸试样;对于中心裂纹拉伸试样,当应力比为正时,应力比增大,疲劳裂纹扩展速率增加,疲劳裂纹扩展平均寿命减小;应力比为负时,裂纹闭合效应导致裂纹扩展加速;负应力比时的裂纹扩展速率大于正应力比,但疲劳裂纹扩展平均寿命明显小于正应力比。     

交变载荷作用下纤维增强密封复合材料界面脱黏研究

界面脱黏是纤维增强密封复合材料界面破坏的主要表现形式,其可视为一种特殊的裂纹扩展。本文基于剪滞模型研究了纤维增强密封复合材料中纤维和基体界面在交变载荷作用下的裂纹扩展规律。在考虑疲劳加载引起的脱黏界面损伤和损伤分布不均匀性以及材料泊松比影响的基础上,建立了等效Paris公式,得到了疲劳裂纹扩展长度、扩展速率、界面上摩擦系数和加载次数之间的关系。     

复合型加载下裂纹疲劳扩展的两种典型

不锈钢材料在复合加载条件下（Ⅰ＋Ⅱ），裂纹的扩展有两种典型，即发生拐弯或分支扩展。通常当双向载荷为同向时，裂纹只改变扩展方向（拐弯），且随着二载荷比λ（＝Ｐｙ／Ｐｘ）从０→１时，转向角β从４５°→０°。当双向载荷为反向时，λ从０→－１，裂纹只发生分支，且分支夹角始终为一定值，二分支在扩展中逐渐平行于二载荷轴。对裂纹尖端的应力强度因子ＫⅠ和ＫⅡ的计算表明，复合加载下裂纹通过拐弯或分支，使ΔＫⅡ→０。拐弯或分支后的裂纹扩展速率可以用ＫⅠ描述。该扩展规律对于指导工程实践有着重要意义     

变幅载荷谱中加载顺序对疲劳裂纹扩展速率的影响

根据某高温高压换热器实际工况载荷波动所编制的载荷谱,用材料为2 1/4Cr-1Mo钢的CT试件,不同的载荷谱加载顺序,进行变幅载荷谱下的疲劳裂纹扩展速率试验研究。根据试验数据和超载迟滞效应理论,讨论了不同载荷谱加载顺序对疲劳裂纹扩展速率的影响。     

焊件疲劳裂纹扩展速率的预测

疲劳是工程中最常见的现象之一,焊件的疲劳裂纹扩展速率的研究为进行疲劳寿命预测提供了基础。本文通过对一定存活率下的疲劳裂纹扩展速率的预测回归分析,得到一个既准确又简便的方法求解 Paris 公式。     

浅谈女儿墙裂缝控制

简介女儿墙裂缝的基本类型、常见位置、形态特征及产生的原因,从设计和施工的角度提出相应的处理措施。     

裂纹形态对丁腈橡胶力学性能和耐疲劳性能的影响

丁腈橡胶为石化行业应用最为广泛的一类橡胶材料。在受到周期应力的作用下，丁腈橡胶内已存在的裂纹会不断扩展而最终导致橡胶断裂。本文考察了预制缺陷的种类及大小对丁腈橡胶疲劳过程中裂纹扩展情况的影响，并对断面形貌进行了观察。结果表明，在圆形、纵向和横向三种缺陷中，纵向缺陷对丁腈橡胶的力学性能和耐疲劳性能影响最小；对圆形缺陷来讲，随孔直径的增大，丁腈橡胶的耐疲劳性能和力学性能逐渐下降。     

用仪表示波系统研究聚丙烯材料的冲击断裂行为

研究了加入一定量成核剂的聚丙烯材料的冲击断裂行为,通过在一般Charpy冲击实验采用仪表示波系统测定了材料的载荷－时间曲线,通过该曲线将冲击断裂过程分为裂纹萌生和裂纹扩展两阶段,并计算出了裂纹萌生功和裂纹扩展功。结果显示,冲击功在成核剂加入量为0．4％处出现极大值,而裂纹萌生功和裂纹扩展功在成核剂加放量为0．4％处出现转折变化,而且裂纹扩展阶段的功耗居于主导地位。     

玻化砖裂纹的产生原因及克服措施

主要论述了裂纹的分类，从生产工序的各个环节分析了裂纹产生的原因，并制定了克服措施。     

玻璃的脆性(四)

综述了裂纹的容忍度与玻璃脆性的关系。对不同品种玻璃的裂纹扩展力也作了阐述。此外,还讨论了应力腐蚀下各种玻璃的裂纹扩展速度和影响裂纹扩展的因素。     

Subcritical Crack Growth in Sintered Silicon Nitride Exhibiting a Rising R-Curve

Subscritical crack growth of sintered silicon nitride was analyzed in terms of the R -curve. Provided that the stress intensity at the crack tip governs the subcritical crack-growth velocity, the K _I– V relationship of sintered silicon nitride exhibiting a rising R -curve is shown to shift to the high- K _I region as the crack advances.     

Atomic picture of crack propagation in Li2O-2SiO2 glass-ceramics revealed by molecular dynamics simulations

Fundamental understanding of the interaction between glass and ceramic phases with a running crack and the mechanisms by which propagation is hindered or altered as compared to the precursor parent glasses remains elusive for the lithium disilicate glass-ceramics. We herein conduct extensive molecular dynamics simulations to reveal some atomic details that are otherwise extremely challenging to be probed by experiments. The results show that the crack propagation pathway in glass-ceramics is dramatically different as compared to the precursor parent glass. In glassy sample, clean crack branching seems to be triggered by multiple cavitation events ahead of crack tip. In glass-ceramic samples, however, branching is characterized by microcracks at multiple glass-nanocrystal interface sites, clean nanocrystal cleavage along certain crystalline plane, and even secondary cracks due to the percolation of multiple microcracks. Additionally, the nanocrystal distribution, total volume fraction, and aspect ratio also have pronounced effects on the propagation of a primary crack and can lead to very diverse crack patterns.     

Crack initiation and propagation in circular rubber bearings subjected to cyclic compression

The fatigue failure mechanism of rubber bearings under cyclic compression is important in evaluating their fatigue lives and thus is analyzed theoretically and numerically here. At first, the stress distributions in a bonded rubber cylinder derived from three different existing models were utilized to calculate the cracking energy densities within it. Next, the location of fatigue crack initiation and the direction of subsequent crack propagation in circular rubber bearings were consecutively determined. Furthermore, finite element numerical results were compared to those obtained theoretically from the three models to check their validity in predicting the fatigue crack initiation and propagation in circular rubber bearings. Based on the quasi‐statically theoretical and numerical results, it is found that the fatigue cracks initiate first at the outermost boundary between rubber and steel plates and propagate later inwards to the center of circular rubber bearings. The corresponding fatigue failure mechanism obtained theoretically and numerically is consistent with experimental findings reported previously. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Crack evolution process of window glass under radiant heating

Window glass breakage has a significant impact on the compartment fire development being sometimes a weak link for fire safety design. This work focuses on the process of crack evolution of window glass in a fire environment. A total of 11 experiments were conducted in a box apparatus by changing heating rate of a heat source. The box apparatus is an enclosed compartment, which includes the heat source, assembled boxes, and glass pane. Crack time, temperature field, breaking stress, crack evolution, and fall‐out of the glass panes are presented. Main and secondary fractures are defined and illustrated in the process of crack evolution. Average time to the first, second, and third main fractures decreased as the heating rate of heat source increased. The average breaking stress was 71.14 MPa for float glass at the time of first main fracture. The crack evolution process was very complicated. Cracks initiated at an edge and propagated towards other edges for main fractures. Multiple cracks were joined together to form cracked glass islands. The fall‐out of cracked glass islands under radiant heating was more difficult than that under real fire scenarios.     

Effect of pH variation on the subcritical crack growth parameters of glassy matrix ceramics

The goals of our study were to calculate the subcritical crack growth (SCG) parameters of two veneering ceramics stored in water or Streptococcus mutans (S. mutans) biofilm and remineralizing medium, with indentation flaws. Feldspar (VM7) and leucite-reinforced (VM13) glass ceramic disks (Vita Zahnfabrik, Bad Säckingen, Germany) were made according to ISO 6872. Some specimens were indented with a Vickers diamond and the crack dimensions were measured. The specimens were fractured for a calculation of inert strength or further stored in water or submitted to pH variation, under preloading tension. Finally, the SCG parameters were calculated after the specimens were fractured under four stressing rates (MPa/s). Weibull analysis was conducted on non-indented specimens. XPS was performed as qualitative analysis. The subcritical crack of leucite ceramic did not vary with the media storage, but the glass-ceramic experienced a retarded growth after pH variation. The materials presented low Weibull modulus. Qualitative elemental analyses showed chemical modification on both ceramics. Therefore, the crack growth of leucite-reinforced ceramic was less affected by the environment pH than glass-ceramic.