浅谈现浇混凝土楼板裂缝在施工过程中的控制

现浇混凝土楼板经常出现裂缝，造成裂缝原因很多，裂缝形成多种多样，本文介绍了裂缝的存在的形式，产生原因，以及在设计施工，原材料控制中采取减少或避免楼板产生裂缝的措施。     

大体积砼产生裂缝的原因及防治措施

大体积砼裂缝问题是建筑业普通关心的问题.对砼裂缝进行控制,就必须研究砼结构中裂缝产生的原因以及在实际的设计和施工过程中采取合理的、经济的措施来控制裂缝.本文通过对大体积砼裂缝成因的理论研究,提出了合理的裂缝控制的设计和施工措施.     

现浇砼楼板施工裂缝的控制及处理

阐述了现浇砼楼板施工裂缝产生的机理、状况及产生的原因，并提出了应抓好砼施工过程中几个重要环节来进行裂缝控制，以及对待施工裂缝的正确态度。     

砌体结构房屋的墙体裂缝控制研究

论述了砌体结构房屋内裂缝出现的原因、形式,以及预防方法和治理的措施等,提出了控制裂缝应以预防为主治理为辅的原则。     

混凝土现浇楼板裂缝分析

针对混凝土现浇楼板的裂缝问题，结合工程施工经验，就裂缝产生的原因进行了分析，并提出了避免产生裂缝应采取的防治措施。     

大型鼓风机基础裂缝的分析及控制

对大型鼓风机基础在实际施工中易产生裂缝的原因进行了技术分析,并提出了合理的裂缝控制措施。通过实践证明,该措施的应用较好的控制了混凝土裂缝问题,保证了混凝土施工质量。     

浅析大体积砼裂缝产生的原因及防治加固方法

本文通过大体积砼裂缝成因的理论分析，提出了合理的裂缝控制的施工措施以及对巳有裂缝采取的处理方法。     

基于改进BiSeNetV2的裂缝检测与识别

裂缝作为固体材料中较为常见的某种不连续现象,是固体结构破坏的开始,及时对裂缝进行识别和检测,并对检测结果进行分析,采取相对应的措施,能够较好地防止事故发生,保障工程作业中的安全。目前裂缝识别主要依靠人工检测,存在劳动强度大、耗时长、精确度不高、危险、耗费高等问题,为此基于数字图像处理技术的裂缝智能识别被广泛研究,然而裂缝表面纹理不规则、噪声的复杂信息,影响了识别精度。为了解决常见固体材料的裂缝智能识别问题,提出了以轻量级语义分割网络模型BiSeNetV2来进行裂缝自动检测,同时自主构建裂缝数据集。实验表明,改进后的裂缝识别模型识别精度提升了7.6%。基于BiSeNetV2的裂缝识别模型,能对裂缝进行精准检测和识别,解决人工识别存在的各类问题。     

浅析混凝土构件中非结构裂缝的成因和控制

结对非结构裂缝中的塑性裂缝、温度收缩裂缝、干缩裂缝的危害、成因及控制进行了分析,并进行了归纳总结。     

混凝土构件中非结构裂缝的成因和控制

对非结构裂缝中的塑性裂缝、温度收缩裂缝、干缩裂缝的危害、成因及控制进行了分析,并进行了归纳总结。     

硅砖中裂纹的成因及其分析

制品受到热冲击后内部会出现热应力，当热应力过大时制品中会产生裂纹。硅砖中裂纹包括表面裂纹和层裂。表面裂纹又分为横向裂纹、竖向裂纹和网状裂纹。通常层裂和竖向裂纹是机压所致，横向裂纹和网状裂纹是烧成造成的。影响裂纹生成的主要因素是烧成和机压，但与生产过程有关的其它因素的作用也不容忽视。     

基于有限元方法的疲劳裂纹闭合行为

裂纹闭合行为将很大程度改变疲劳裂纹扩展行为。针对316L不锈钢,结合常幅加载和单个拉伸过载试验和动态数值模拟方法,对疲劳裂纹扩展行为中的裂纹闭合现象开展了一系列研究工作。详细对比了不同扩展阶段的裂纹闭合行为随裂纹长度、应力比和过载影响因素的变化,以及对裂纹扩展速率的影响。同时,研究了单个拉伸过载和裂纹闭合行为之间的内在联系和机理。结合裂纹闭合理论和有限元计算结果,等效应力强度因子被用来描述316L不锈钢的裂纹扩展过程,并提出316L不锈钢的裂纹扩展速率的预测模型。     

Simulation of crack propagating in discontinuously reinforced metal matrix composite

A fracture mechanics-based numerical simulation of a crack propagating under mode I loading through discontinuously reinforced metal matrix composites (MMCs) is presented. Microcrack initiation due to debonding and breakage of reinforcements, shielding and antishielding effects caused by both microcracks and the reinforcements, the effect of crack deflection, and growing crack singularity are considered in the calculation of local crack tip driving forces. Statistical variations of spatial distribution and strength of the reinforcements are also considered. The essential feature of the model is to predict crack initiation toughness and crack path morphologies using a mixed-mode crack propagation criterion. Application of the program to predict crack growth behavior in an SiC whisker/Al alloy composite is presented. Microcracking far ahead of the tip of a main crack, crack deflection toward the microcracks, and subsequent incorporation of the microcracks which most affect the main crack are well simulated. The predicted microcrack distribution and variation of mixed-mode crack tip driving forces with crack growth are also evaluated.     

Effect of crack surface geometry on fatigue crack closure

The geometry of crack faces often plays a critical role in reducing crack extension forces when crack closure occurs during fatigue crack growth. Most previous studies of fatigue crack closure are concerned with mechanical measures of closure as related to the crack growth rate; very little attention has been given to the geometry of the crack surfaces. Our objective is to identify those aspects of crack surface geometry that are important in the closure process, to develop quantitative fractographic techniques to estimate such attributes in a statistically significant and robust manner, and to correlate them to the physical process of crack closure. For this purpose, fatigue crack propagation experiments were performed on a Ni-base superalloy and crack growth rates and crack closure loads were measured. Digital image profilometry and software-based analysis techniques were used for statistically reliable and detailed quantitative characterization of fatigue crack profiles. It is shown that the dimensionless, scale-independent attributes, such as height-to-width ratio of asperities, fractal dimensions, dimensionless roughness parameters,etc., do not represent the aspects of crack geometry that are of primary importance in the crack closure phenomena. Furthermore, it is shown that the scaledependent characteristics, such as average asperity height, do represent the aspects of crack geometry that play an interactive role in the closure process. These observations have implications concerning the validity of geometry-dependent, closure-based models for fatigue crack growth.     

0.13C-5Mn中锰钢的裂纹扩展行为

 为了研究基体组织为铁素体和亚稳奥氏体的0.13C-5Mn中锰钢裂纹扩展特性,采用载荷控制对其进行裂纹扩展试验,采用SEM、EBSD等手段表征了裂纹扩展行为。研究结果表明,裂纹扩展机制为滑移和积累损伤双重机制。在裂纹尖端的塑性区内发生亚稳奥氏体转变为马氏体的相变,发生转变的区域远远小于裂纹尖端塑性区尺寸,由于相变吸收了能量以及裂纹闭合效应降低了疲劳裂纹扩展速率。     

Effects of crack aspect ratio on the behavior of small surface cracks in fatigue: Part I. Simulation

A simple simulation of alternate growth of a small surface crack in the surface and depth directions was performed to illustrate the changes in crack aspect ratio, induced by grain boundaries, as a function of crack size. It is shown that at small crack sizes, large variations in aspect ratio, a/c (a is the crack depth and c is the half-surface length), occur, due to local crack front perturbations induced by grains that are oriented for crack growth. At these crack sizes, the assumption of a semicircular crack shape (a/c=1.0) was found to cause errors in stress intensity range (ΔK) calculations. This, in turn, led to significant scatter or “anomaly” in small crack growth rates relative to large cracks. At large crack sizes, the effects of local crack front perturbations on crack aspect ratio and ΔK were found to be insignificant. As a result, the scatter in crack growth data was found to decrease to a negligible level at large crack sizes. It is suggested that the limiting crack size above which the small crack behaves as a large crack, l ₂=10d (d = grain size), proposed by Taylor and Knott, is related to the crack size above which the effects due to aspect ratio variations are small.     

A microscopic model of hydrogen-induced intergranular cracking—II. Steady state crack growth

A steady state model of hydrogen-induced intergranular crack growth has been developed. It is assumed that the steady state growth of an intergranular crack, screened by dislocations, is controlled by the grain boundary and crack surface diffusion processes of hydrogen. A series of second-order differential equations controlling the diffusion processes of hydrogen in the intergranular crack regions is solved numerically to determine the hydrogen distribution along a steadily moving crack and thereby the change of the ideal work of fracture. The relationship of the stress intensity required for the crack growth to the crack velocity is established as a function of several values of the grain boundary and crack surface diffusivities, the crack length, and the grain size. It is found that while the susceptibility to hydrogen-induced intergranular crack growth increases with increasing hydrogen diffusivities, it decreases with increasing crack length and grain size. The effect of grain size on the growth characteristics of hydrogen-induced intergranular cracking are discussed in terms of the direction change of the hydrogen flux along the moving crack.     

连铸板坯内裂预测模型研究初探

在利用硫印图像自动判级系统得到的内裂定量化数据的基础上,结合连铸板坯内裂产生机理,对内裂进行了统计分析。结果表明,内裂的发生是有一定规律的,从预测板坯内裂的级别来说,开发预测模型是可行的。并以统计分析得到的一内裂预测模型作为实例进行了说明。     

Criminal activity and crack addiction

The association of crack and criminal activity is commonly believed but not well documented or characterized in any systematic studies of crack addicts. In this survey of 200 crack addicts, daily use of crack correlated more with illicit, criminal activities to obtain a supply of crack than to demographic features. Correspondingly, felony and cocaine dealing was associated with total dollars spent on cocaine but not to other demographic features such as level of property or affluence. Moreover, the majority of crack addicts in this sample used cocaine intranasally before starting crack use. The mean age from onset of crack use to seeking help for cocaine addiction is less than 3 years. Severity of crack use and addiction as measured by daily use was associated with psychosocial consequences more than other demographic features.