Peri-Net-Pro: the neural processes with quantified uncertainty for crack patterns

This paper develops a deep learning tool based on neural processes(NPs)called the Peri-Net-Pro,to predict the crack patterns in a moving disk and classifies them according to the classification modes with quantified uncertainties.In particular,image classification and regression studies are conducted by means of convolutional neural networks(CNNs)and NPs.First,the amount and quality of the data are enhanced by using peridynamics to theoretically compensate for the problems of the finite element method(FEM)in generating crack pattern images.Second,case studies are conducted with the prototype microelastic brittle(PMB),linear peridynamic solid(LPS),and viscoelastic solid(VES)models obtained by using the peridynamic theory.The case studies are performed to classify the images by using CNNs and determine the suitability of the PMB,LBS,and VES models.Finally,a regression analysis is performed on the crack pattern images with NPs to predict the crack patterns.The regression analysis results confirm that the variance decreases when the number of epochs increases by using the NPs.The training results gradually improve,and the variance ranges decrease to less than 0.035.The main finding of this study is that the NPs enable accurate predictions,even with missing or insufficient training data.The results demonstrate that if the context points are set to the 10th,100th,300th,and 784th,the training information is deliberately omitted for the context points of the 10th,100th,and 300th,and the predictions are different when the context points are significantly lower.However,the comparison of the results of the 100th and 784th context points shows that the predicted results are similar because of the Gaussian processes in the NPs.Therefore,if the NPs are employed for training,the missing information of the training data can be supplemented to predict the results.

Simulation of Crack Pattern Formation Due to Shrinkage in a Drying Material

Crack patterns observed in nature have attracted the interest of researchers in various fields, and the mechanism of the pattern formation has been investigated. However, the phenomenon is very complicated, and many factors affect the process. Therefore, we are motivated to construct a general simulation code with a simple algorithm. In this study, crack pattern formation due to shrinkage caused by the drying of a wet material was simulated. The process was simplified as follows: tensile force is generated in the model, and a crack is generated when the tension exceeds a critical value. The tensile forces in the x and y directions are independently evaluated. A crack propagates perpendicular to the tension until it reaches another crack or a boundary. Based on this modeling, simulations with a two-dimensional square domain were performed. Consequently, a cross-divided pattern was generated. Assuming zigzag crack propagation, more realistic patterns were obtained. The effects of the boundary and domain size were also considered, and various characteristic patterns were obtained. Furthermore, the orientation dependency was simulated, and 45&#730 declined patterns and rectangularly divided patterns were generated. The model presented in this study is very simplified and is expected to be applicable to various objects.

Crack patterns corresponding to the residual strength plateau of ceramics subjected to thermal shock

The formation strength plateau of ceramics is addressed. A set of of 99A1203 are conducted, mechanism of the residual subjected to thermal shock thermal shock experiments where the thin specimens of 1 mm× 10 mm×50 mm exhibit parallel through edge cracks, and thus permit quantitative measurements of the crack patterns. The cracks evolve with the severity of ther- mal shock. It is found that there is a correlation between the length and density of the thermal shock cracks. The increase of crack length weakens the residual strength, whereas the increase of crack density improves it. In a considerably wide temperature range, the two contrary effects just counteract each other; consequently a plateau appears in the variation curve of the residual strength. A comparison between the numerical and experimental results of the residual strength is made, and they are found in good agreement. This work is helpful to a deep understanding of the thermal shock failure of ceramics.

Stable and realistic crack pattern generation using a cracking node method

This paper presents a method for simulating surface crack patterns appearing in ceramic glaze, glass, wood and mud. It uses a physically and heuristically combined method to model this type of crack pattern. A stress field is defined heuristically over the triangle mesh of an object. Then, a first-order quasi-static cracking node method （CNM） is used to model deformation. A novel combined stress and energy combined crack criterion is employed to address crack initiation and propagation separately according to physics. Meanwhile, a highest-stress-first rule is applied in crack initiation, and a breadth-first rule is applied in crack propagation. Finally, a local stress relaxation step is employed to evolve the stress field and avoid shattering artifacts. Other related issues are also discussed, such as the elimination of quadra- ture sub-cells, the prevention of parallel cracks and spurious crack procession. Using this method, a variety of crack patterns observed in the real world can be reproduced by changing a set of parameters. Consequently, our method is robust because the computational mesh is independent of dynamic cracks and has no sliver elements. We evaluate the realism of our results by comparing them with photographs of realworld examples. Further, we demonstrate the controllability of our method by varying different parameters.

Cracking Patterns of Shear Walls in Reinforced Concrete Structure due to Strong Earthquake Based on Mohr-Coulomb Criterion

A primary goal of seismic design of buildings is to protect people's life safety during strong earthquakes. Fundamentally,to predict the survived space and estimate people escape intervals during structural collapse are very important,which requires to describe the failure process more detailedly not only for structural joints but also for slabs and shear walls. In the present paper,the details of Mohr-Coulomb failure criterion with tension-cutoff together with its expression in failure surface and local coordinate system of reinforced concrete( RC) shear wall are given firstly,and then several typical cracking patterns of RC shear wall,such as tension shear crack and compression shear crack, are analyzed based on Mohr-Coulomb failure criterion with tension-cutoff.

Research on cracking mechanism of the thin shell mould in expendable pattern shell casting during pattern removal process

Aiming at the cracking phenomenon of the thin shell mould in the expendable pattern shell casting during the pattern removing process, some systemic researches are presented.The influence of the pattern removing method and temperature on the pattern removing were investigated.The shell mould cracking mechanism was analyzed by using thermo-gravimetric analysis (TGA), and combining the temperature field and the volume change of the expanded polystyrene (EPS) foam pattern being tested.The results indicated that the shell mould was not easily cracked when the pattern removing process was carried out with the furnace being heated little by little because of the shell slowly shrinking with dehydration and shell strength gradually increasing.The shell mould was soon destroyed when it was set directly into the furnace at above 400 oC because of the thin shell mould rapidly shrinking and the foam pattern hindering.However, the shell mould had no cracking when it had been preheated for a long time even if the furnace temperature was above 400 oC and the shell was put into the furnace directly.Moreover, when the shell mould was directly set into the furnace at lower temperatures, 250 to 300 ℃, the shell would shrink slowly and the foam pattern would stay at the maximum expansion stage temperature of 100 to 110 ℃ for a long time; and the shell mould would experience an expansion force from the foam pattern for a long time.The expansion force is related to the pattern removing temperature, holding time, foam pattern thickness and density.Therefore, the foam pattern with higher density could make the shell crack.

轴向静载压缩作用下深部砂岩的变形破坏规律

为探究深部砂岩的变形破坏规律,建立塑性区发育、裂纹扩展情况和声发射特征之间的关系。以深部砂岩岩样为研究对象,开展轴向静载压缩声发射试验,并采用数值模拟分析岩样塑性区和内部裂纹的演化规律。结果表明:内部能量密度在压密和弹性阶段耗散比较平稳,塑性阶段耗散能逐渐增大,在破坏前瞬间全部释放。塑性区、裂纹和声发射特征间具有很强的关联性,压密阶段振铃计数、能量均是先增大后减小,弹性阶段前处于平静期,塑性区和微裂纹均从岩样两端侧面出现。弹性阶段,振铃计数和能量继续增大,后者涨幅大于前者,塑性区沿对角线向内发育,裂纹数量增多。塑性阶段,振铃计数持续增大,能量激增,塑性区向外发育。破坏阶段,振铃计数和能量均出现激增,模拟试验为“y”状剪切裂纹,与实际破坏裂纹形态一致。

负压差斜管内催化剂颗粒流动特性的实验研究

在规格为Φ150 mm×3600 mm的负压差斜管-阀门实验装置上,通过测量和分析不同催化剂颗粒质量流率(G_(s))时斜管内轴向动态压力的特征参数,进行催化裂化装置斜管内催化剂颗粒的流动特性研究。结果表明:斜管蓄压能力随G_(s)的增大而增大,管内依次出现稀相分层流、密相分层流和填充流;斜管内的压力分布、主频、幅值、标准偏差与流态相对应,可用于流态的量化识别;当G_(s)=65.96 kg/(m^(2)·s)时,斜管内存在多流态,分别为过渡填充流、填充流、密相流;在斜管中部通入松动风,可以有效改善颗粒输送能力和斜管蓄压能力。

闪长岩破裂的声发射前兆现象及其裂纹路径演化规律

为了研究岩石破裂过程中裂纹扩展路径演化规律,基于声发射监测数据,结合矩张量反演、裂纹尺度量化及裂纹拓扑关系量化建立了裂纹扩展路径分析方法,并基于室内声发射试验分析了闪长岩单轴压缩破坏过程。研究结果表明:闪长岩在受载过程中产生微裂纹的特征尺度为1.06 mm,明显高于矿物颗粒的平均尺度;随着应力的增加,闪长岩试件内部的微裂纹由离散状态逐渐过渡为相互贯通状态,微裂纹相对集中区域更容易演化为宏观裂纹。

0Cr12Mn5Ni4Mo3Al不锈钢自锁螺母的开裂原因

某0Cr12Mn5Ni4Mo3Al不锈钢自锁螺母在服役过程中出现开裂。对开裂螺母进行了宏观和微观断口形貌观察、表面能谱分析、显微组织及力学性能分析与测试等。结果表明:该螺母开裂原因为应力腐蚀开裂(SCC)。裂纹起源于法兰面与螺母体交接处,螺母体与法兰面呈直角此处易积液,螺母表面处理方式为钝化和涂MoS_(2),其耐蚀能较差。在腐蚀性潮湿大气环境中,干湿交替作用下螺母产生局部腐蚀点,在腐蚀点处萌生裂纹,裂纹在螺母圆周切向拉应力作用下扩展直至螺母开裂。

A state-of-the-art review of mechanical characteristics and cracking processes of pre-cracked rocks under quasi-static compression

The mechanical characteristics and failure behavior of rocks containing flaws or discontinuities have received wide attention in the field of rock mechanics.When external loads are applied to rock materials,stress-induced cracks would initiate and propagate from the flaws,ultimately leading to the irreversible failure of rocks.To investigate the cracking behavior and the effect of flaw geometries on the mechanical properties of rock materials,a series of samples containing one,two and multiple flaws have been widely investigated in the laboratory.In this paper,the experimental results for pre-cracked rocks under quasistatic compression were systematically reviewed.The progressive failure process of intact rocks is briefly described to reveal the background for experiments on samples with flaws.Then,the nondestructive measurement techniques utilized in experiments,such as acoustic emission(AE),X-ray computed tomography(CT),and digital image correlation(DIC),are summarized.The mechanical characteristics of rocks with different flaw geometries and under different loading conditions,including the geometry of pre-existing flaws,flaw filling condition and confining pressure,are discussed.Furthermore,the cracking process is evaluated from the perspective of crack initiation,coalescence,and failure patterns.

Numerical Simulation of the Behavior of Cracked Reinforced Concrete Members

Refined non-linear static or dynamic analyses of reinforced concrete structures require the knowledge of the actual force-displacement or bending moment-rotation curves of each structural member, which depend on the crack widths and on the crack pattern, and after all on the slip between concrete and reinforcing steel. For this reason the definition of improved local models taking into account all these local aspects is a fundamental prerequisite for advanced assessment of r.c. structures. A numerical procedure which allows to predict the relative displacement between steel reinforcement and the surrounding concrete in a reinforced concrete element, once assigned the stress in the naked steel bar and the bond-slip law is discussed. The method provides as final outcomes the sequence of crack openings and the individual crack widths, regardless of the particular bond-slip correlation adopted. The proposed procedure is implemented referring to two relevant experimental case studies, demonstrating that it is able to predict satisfactorily actual strain fields and slips along the investigated reinforced concrete elements.

基于裂隙扩展的多级岩质边坡开挖卸荷破坏路径分析

开挖卸荷作用下裂隙岩体边坡的破坏模式与路径分析是边坡工程灾害研究的热点之一,准确识别边坡的潜在破裂路径对工程安全施工和支护优化设计具有重要意义。依据断裂扩展分析方法,将裂隙扩展判别的理论方法开发并应用于数值模拟分析中,通过裂隙尖端应力强度因子计算、裂隙扩展模式识别、裂隙起裂角演算、裂隙扩展交汇等技术实现了岩体中断续裂隙的起裂、扩展与贯通演化过程的快速模拟;以某高速公路沿线裂隙岩体路堑边坡为对象,采用提出的模拟方法分析了多级开挖卸荷作用下坡体裂隙的扩展机制与边坡的破坏路径。结果表明:裂隙岩体边坡从上至下多级开挖过程中,坡肩裂隙首先起裂,并通过拉张型扩展逐渐发展为优势裂隙;随着边坡下挖,优势裂隙沿坡面向下逐步发生拉张/剪切混合型扩展并与既有裂隙交汇,在边坡中上部形成阶梯状扩展破坏路径;裂隙扩展至边坡下部及坡脚后扩展模式由拉张/剪切混合型转化为剪切型,并最终以弧形剪切面从坡脚出露。研究揭示了裂隙岩体边坡多级开挖卸荷作用下上部阶梯状拉张/剪切混合型破裂-下部弧形剪切型破裂的复合破坏模式,可为边坡工程支护设计和施工稳定性控制提供新思路。

深井扇形组合孔短延时爆破裂纹扩展模拟研究

提出了一种扇形组合孔短延时爆破的构想,即在常规的每排扇形崩落孔中间增加一排致裂孔,崩落孔与致裂孔之间短延时间隔起爆。使用ANSYS/LS-DYNA对不同延时时间及不同围压加载条件下的爆破方案进行数值模拟研究,发现高应力环境下常规扇形孔爆破无法形成有效爆破漏斗,扇形组合孔短延时爆破则损伤破裂更加有效、破岩效果更好。此外对不同围压条件下的裂纹扩展进行分析,爆破裂纹扩展趋向于最大主应力方向。数值模拟及现场工程实践证实,当最大主应力方向与扇形崩落排孔成一定小角度,即平行崩落排孔方向加载较大围压、垂直排孔方向加载较小围压时,扇形组合孔短延时爆破不仅可以改善岩石破碎效果,也可以有效保护后排炮孔和保留岩体。

盾构法隧道施工期间管片裂损分布规律及原因分析

为了查明盾构法隧道施工期间管片裂损原因,以西安某地铁线盾构法隧道施工期间管片封顶块裂损现象为例,统计隧道管片裂损情况,分析隧道管片裂损分布规律。分析封顶块受力情况,判断隧道管片裂损原因;采用SolidWorks建立管片模型并导入ABAQUS软件,模拟计算管片和螺栓孔应力状态。分析结果表明:拱顶处管片裂损率最高,拱底次之,拱腰两侧最小。封顶块管片裂损率高,主要原因为管片间施加传力衬垫,导致管片间静摩擦力减小,在千斤顶油缸收缩过程中,封顶块管片容易产生相对位移,螺栓孔处受力较大,导致管片裂损。

土体干缩裂隙网络定量分析

土体干缩裂隙网络定量分析对深入研究裂隙发育机制及正确评价裂隙土的工程性质有重要意义。在室内对三组不同土体开展了干燥试验,采用数字图像处理技术对获得的裂隙图像进行了二值化、除噪和骨架化等预处理操作,提出了一整套与裂隙网络几何形态特征密切相关的量度指标体系并进行了定量分析,借助概率密度函数,从统计学角度探讨了关键量度指标的分布特征。结果表明:土质对干缩裂隙网络的几何形态特征有重要影响,表面裂隙率、裂隙节点个数、裂隙总长度、裂隙平均宽度和土块个数通常随黏粒含量和塑性指数的增加而增加;量度指标之间既有区别又有联系,如表面裂隙率与裂隙平均宽度存在正相关性,裂隙条数受节点个数的控制,土块个数越多,则对应土块平均面积越小,表面裂隙率越大,分形维数也越大;单位面积内的节点个数、土块个数和表面裂隙率可作为定量描述裂隙网络几何形态特征的基本指标;裂隙长度、宽度和土块面积的平均值与它们的主要分布范围及最可几值之间存在较好的相关性。

钢筋混凝土梁裂缝分型试验研究及统计分析

通过20根钢筋混凝土简支梁的试验,研究了纵向受拉钢筋和混凝土保护层厚度对裂缝分布形态的影响规律。根据各条裂缝的产生机理、延伸发展的特征和宽度变化规律,提出了钢筋混凝土梁的裂缝分型统计分析原则,确定了结构设计中裂缝宽度验算对应的裂缝形态特征,提出了以截面高度和纵向受拉钢筋直径为变量的纵向受拉钢筋有效影响区即有效受拉截面面积的计算方法,进行了平均裂缝间距、平均裂缝宽度及裂缝宽度扩大系数分布规律的统计分析。

配置500MPa钢筋的混凝土梁裂缝试验研究

为研究配置500 MPa纵向热轧带肋钢筋的混凝土梁的裂缝特征及评估相关规范裂缝计算公式的适用性,进行了22根钢筋混凝土梁受弯性能试验,得到22个平均裂缝间距和92组裂缝宽度数据,相应的钢筋应力范围在201~482MPa,这些试验数据可反映钢筋应力较高情况下受弯构件的裂缝开展特点.试验结果表明,按规范GB50010—2002公式计算的平均裂缝间距、平均裂缝宽度和最大裂缝宽度比试验值普遍偏大,二者之比的均值分别为1.127,1.557和1.535.根据试验结果,提出配置500 MPa带肋钢筋的混凝土梁的裂缝宽度计算公式修正建议,并给出梁侧面钢筋处和受拉边缘的平均裂缝宽度的换算关系式,建议公式的计算值和试验值符合较好.

运用Image J软件分析土壤结构特征

以土壤团聚体、土壤裂隙以及土壤优先流特征数码图像为研究对象,介绍了ImageJ软件在土壤结构特征分析中的应用。研究结果表明:①马尾松林地表层土壤团聚体圆度大于母质层土壤颗粒的圆度;②运用图像测量方法能够快速地测定土壤裂隙几何特征以及土壤收缩曲线;③土壤优先流示踪图像分析结果显示红壤性水稻土犁底层具有显著的防渗功能,而同一土壤剖面内土壤连通性孔隙存在较大的空间分异。最后,本文还对以上研究结果和图像分析方法进行了探讨。

基于近场动力学方法的混凝土板侵彻问题研究

由于近场动力学(Peridynamics)用统一空间积分-时间微分方程描述物体连续或不连续区域,改进常用微观弹脆性模型(Prototype Microelastic Model,PMB)对势本构力函数,给出刚性体与变形体冲击问题接触算法;编制计算程序,验证经典简支梁变形及Kalthoff-Winkler试验;数值模拟刚性弹丸侵彻混凝土矩形板破坏过程,揭示损伤累积及裂纹扩展全过程与最终破坏形态。结果表明,改进的近场动力学模型及算法合理、可靠,能有效模拟混凝土结构冲击破坏及侵彻问题。