Mechanical properties of AISI 1045 ceramic coated materials by nano indentation and crack opening displacement method

An effective approach was conducted for estimating fracture toughness using the crack opening displacement (COD) method for plasma enhanced chemical vapor deposition (PECVD) coating materials.For this evaluation,an elastoplastic analysis was used to estimate critical COD values for single edge notched bending (SENB) specimens.The relationship between fracture toughness (KIC) and critical COD for SENB specimens was obtained.Microstructure of the interface between Al2O3-TiO2 composite ceramic coatings and AISI 1045 steel substrates was studied by using scanning electron microscope (SEM).Chemical compositions were clarified by energy-dispersive X-ray spectroscopy (EDS).The results show that the interface between of Al2O3-TiO2 and substrate has mechanical combining.The nanohardness of the coatings can reach 1 200 GPa examined by nanoindentation.The KIC was calculated according to this relationship from critical COD.The bending process produces a significant relationship of COD independent of the axial force applied.Fractographic analysis was conducted to determine the crack length.From the physical analysis of nanoindentation curves,the elastic modulus of 1045/Al2O3-TiO2 is 180 GPa for the 50 μm film.The highest value of fracture toughness for 1045/Al2O3-TiO2-250 μm is 348 MPa·ml/2.

Strip-coalesced interior zone model for two unequal collinear cracks weakening piezoelectric media

In this paper, a mathematical strip-saturation model is proposed for a poled transversely isotropic piezoelectric plate weakened by two impermeable unequal-collinear hairline straight cracks. Remotely applied in-plane unidirectional electromechanical loads open the cracks in mode-I such that the saturation zone developed at the interior tips of cracks gets coalesced. The developed saturation zones are arrested by distributing over their rims in-plane normal cohesive electrical displacement. The problem is solved using the Stroh formalism and the complex variable technique. The expressions are derived for the stress intensity factors （SIFs）, the lengths of the saturation zones developed, the crack opening displacement （COD）, and the energy release rate. An illustrative numerical case study is presented for the poled PZT-5H ceramic to investigate the effect of prescribed electromechanical loads on parameters affecting crack arrest. Also, the effect of different lengths of cracks on the SIFs and the local energy release rate （LERR） has been studied. The results obtained are graphically presented and analyzed.

Solution of stress intensity factors of multiple cracks in plane elasticity with eigen COD formulation of boundary integral equation

The concept of eigen crack opening displacement （COD） can be defined as the COD of a crack in infinite plate under the tractions acting on the crack surface. By introducing this concept, the eigen COD formulation of boundary integral equation is proposed in this paper, together with the solution procedures for multiple crack problems in plane elasticity. With the proposed approach, the multiple crack problems can be solved with the conventional displacement discontinuity boundary integral equations in an iterative fashion with a small size of system matrix as that in the numerical Green’s function （NGF） approach but without the trouble to determine the complementary solutions since the standard boundary element discretization on the crack surface is no longer required with the proposed approach. Some numerical examples computing the stress intensity factors are presented and compared with those in literature to show the accuracy and the effectiveness of the proposed approach.

基于材料断裂韧度测试的COD换算方法研究

考虑到断裂韧度J积分塑性分量的塑性功由载荷与加载线位移关系得到,通过测试CT(compact tension)和SEB(single edge bending)试样的裂纹嘴张开位移实现J积分计算,提出适用于两种试样的裂纹嘴张开位移与加载线张开位移转换的换算公式,并采用45钢CT试样和30CrMo钢SEB试样对新公式进行有限元数值比对和试验比对。结果表明,新公式结果与规范演算结果之间的相对误差不超过0.4%,与有限元分析结果之间的相对误差不超过0.6%,与CT试样试验结果之间的相对误差小于4.5%,与SEB试样试验结果之间的相对误差小于6%。

基于SSA-BP的露天矿山边坡位移变形预测

针对传统的BP神经网络在预测露天矿山边坡位移变形时存在的局限性,构造了一种基于麻雀搜索算法(SSA)和BP神经网络相结合的边坡位移变形预测模型,先利用麻雀搜索算法对传统的BP神经网络进行权值与阈值的优化,再将麻雀搜索算法优化后的BP神经网络算法(SSA-BP)运用于露天矿山边坡位移的预测。为了验证算法的可行性,将SSA-BP预测模型与WOA-BP、BP以及Elman预测模型针对露天矿山边坡位移变形量的预测结果进行比较。实验结果表明:SSA-BP预测模型针对露天矿山边坡位移变形量的预测相比其他三种模型,其迭代速度快、寻优能力强;通过预测精度评价指标来看,SSA-BP算法的R2、RMSE、MAPE、MAE、MSE明显优于另外三组算法。为露天矿山边坡位移变形预测提供了一种新的思路和方法。

基于深度学习的复合材料开孔板拉伸失效行为预测

为研究复合材料开孔板在拉伸载荷下的失效行为,基于开孔板的拉伸试验建立了高精度的有限元仿真模型,并批量生成了拉伸载荷-位移曲线的数据集。提出了一种双长短时记忆(Long short-term memory,LSTM)神经网络模型用于预测载荷-位移曲线,其中第1个LSTM模型进行输入特征的提取,第2个LSTM模型直接给出载荷-位移曲线的预测。结果表明:这一模型能够高效、准确地预测开孔板的拉伸载荷-位移曲线,在测试集上的决定系数R2可以达到0.9755,关键特征如初始刚度E0的预测误差仅为1.85%,极限载荷Fmax的预测误差仅为2.16%。

Seismic stability analysis of concrete gravity dams with penetrated cracks

The seismic stability of a cracked dam was examined in this study. Geometric nonlinearity and large deformations, as well as the contact condition at the crack site, were taken into consideration. The location of penetrated cracks was first identified using the concrete plastic-damage model based on the nonlinear finite element method （FEM）. Then, the hard contact algorithm was used to simulate the crack interaction in the normal direction, and the Coloumb friction model was used to simulate the crack interaction in the tangential direction. After verification of numerical models through a case study, the seismic stability of the Koyna Dam with two types of penetrated cracks is discussed in detail with different seismic peak accelerations, and the collapse processes of the cracked dam are also presented. The results show that the stability of the dam with two types of penetrated cracks can be ensured in an earthquake with a magnitude of the original Koyna earthquake, and the cracked dam has a large earthquake-resistant margin. The failure processes of the cracked dam in strong earthquakes can be divided into two stages： the sliding stage and the overturning stage. The sliding stage ends near the peak acceleration, and the top block slides a long distance along the crack before the collapse occurs. The maximum sliding displacement of the top block will decrease with an increasing friction coefficient at the crack site.

PERIODICAL INTERFACIAL CRACKS IN ANISOTROPIC ELASTOPLASTIC MEDIA

By using Fourier transformation the boundary problem of periodical interfacial cracks in anisotropic elastoplastic bimaterial was transformed into a set of dual integral equations and then it was further reduced by means of definite integral transformation into a group of singular equations. Closed form of its solution was obtained and three corresponding problems of isotropic bimaterial, of a single anisotropic material and of a bimaterial of isotropy- anisotropy were treated as the specific cases. The plastic zone length of the crack tip and crack openning displacement ( COD) decline as the smaller yield limit of the two bonded materials rises, and they were also determined by crack length and the space between two neighboring cracks . In addition , COD also relates it with moduli of the materials .

STUDY ON THE RELATIONSHIP BETWEEN J-INTEGRAL AND COD

J-integral arid crack opening displacement 8 （COD） were important parameters for characterization of fractures in engineering materials. The relationship between J-integral arid COD has been investigated for a long time and was generally represented as J = m σy, δ, where σy is the yield strength arid m is a function of specimen geometry arid material properties. To determine the value of m, extensive studies and experiments have been performed. The method that used the fracture-surface topography analysis （ FRASTA ） for determining J-integral from fracture surfaces of materials was introduced. On the basis of the relationship between COD arid fracture surface average profile, the relationship between J-integral arid COD was deduced arid compared with the generally used equation. The method was experimentally confirmed to be able to provide a new way to determine the relationship between J-integral and COD.

基于POT模型的泄水闸检修门库裂缝开合度安全监控指标拟定

针对传统混凝土裂缝开合度安全监控指标拟定中对监测数据利用率不高,对数据尾部特征刻画差,导致拟定监控指标精度低的问题,本文结合王甫洲水利枢纽泄水闸检修门库近一年的裂缝实测资料,首先选取涉及汛期、高低温季节等不利工况作用下的典型裂缝开合度监测资料系列作为样本数据,然后引入POT模型拟定了裂缝开合度监控指标,最后对所拟定的裂缝开合度监控指标进行分析评价.结果表明,相对于典型小概率法拟定的监控指标,由于POT模型具有对采集信息利用率高、能够更好地刻画数据分布的尾部特征的优点,该方法拟定的裂缝开合度监控指标精度更高.

管道环焊缝根部裂纹的有限元评价方法研究

油气管道输送介质具有易燃、易爆特性,运营风险高,特别是管道环焊缝出现裂纹的危害更大,在疲劳应力的作用下易发生事故。本文针对某长输管道内检测中环焊缝根部裂纹,建立有限元模型,采用SMAW单V型坡口形式,对环焊缝裂纹尖端网格进行局部加密处理,建立了裂纹扩展驱动力CTOD随轴向载荷的变化模型,得到了管道在相应轴向应力水平下不同裂纹尺寸对应的CTOD值,基于BS 7910以及SY/T 6477关于CTOD与应力强度因子K以及夏比冲击功的经验公式,得到了对应的夏比冲击功,通过我国管道材料CTOD值和夏比冲击功数值的综合判断,可得出管道处于安全状态的结论,对于管道环焊缝根部裂纹缺陷的精准评估具有重要意义。

DETERMINATION OF CRACK SURFACE DISPLACEMENTS FOR A RADIAL CRACK EMANATING FROM A SEMI-CIRCULAR NOTCH USING WEIGHT FUNCTION METHOD

A radial crack emanating from a semi-circular notch is of significant engineering importance. Accurate determination of key fracture mechanics parameters is essential for damage tolerance design and fatigue crack growth life predictions. The purpose of this paper is to provide an efficient and accurate closed-form weight function approach to the calculation of crack surface displacements for a radial crack emanating from a semi-circular notch in a semi-infinite plate. Results are presented for two load conditions： remote applied stress and uniform stress segment applied to crack surfaces. Based on a correction of stress intensity factor ratio, highly accurate analytical equations of crack surface displacements under the two load conditions are developed by fitting the data obtained with the weight function method. It is demonstrated that the Wu- Carlsson closed-form weight functions are very efficient, accurate and easy-to-use for calculating crack surface displacements for arbitrary load conditions. The method will facilitate fatigue crack closure and other fracture mechanics analyses where accurate crack surface displacements are required.

基于弥散与分离裂缝模型的混凝土开裂比较研究

裂缝扩展是影响混凝土结构非线性响应的重要因素,其扩展深度与张开位移是评价结构安全性的重要指标。基于弥散裂缝框架,该文建立了等效裂缝张开位移与损伤因子、断裂带宽度之间的函数关系。分别采用弥散、分离两类裂缝模型模拟I型断裂和I-II混合型断裂试验,二者在结构承载力、裂缝扩展和裂缝张开位移方面均获得了基本一致的结果。数值算例表明弥散裂缝模型与分离裂缝模型计算精度接近但其效率更高。

两种热模拟体系下有机质生气特征对比

对海相Ⅱ1型有机质在封闭体系和开放体系下开展了产气率热模拟实验,并对其在两种体系下的产气率和生气模式进行了对比研究。在开放体系下,样品产气率较低,Ⅱ1型有机质产气率为84.2m3/吨·TOC,但在封闭体系下实验热模拟产气率很高,Ⅱ1型有机质产气率可达371.2m3/吨.TOC;在开放体系下Ⅱ1型有机质大量生气阶段Ro为1.0%～1.5%之间,在封闭体系下Ⅱ1型有机质大量生气阶段在Ro在1.5%～2.5%之间。在不同实验体系下有机质产气率和生气模式的差异主要与有机质的生气机理有关,在开放体系下有机质主要为干酪根裂解气,而在封闭体系下有机质生成的天然气为原油和干酪根裂解的混合气。

混凝土重力坝抗震配筋加固措施的效果研究

混凝土坝遭遇强烈地震导致坝体严重受损已有先例。工程界建议布置坝面钢筋以提高坝体抗震性能。基于此,本文应用嵌入式滑移模型和钢筋刚化模型模拟混凝土重力坝配筋前后的地震动力响应,据此评价坝面配筋措施的抗震效果。计算结果显示,配筋前后结构整体响应基本一致,但布置坝面钢筋后坝体裂缝由集中裂缝分散为多条裂缝,裂缝张开位移和扩展深度较配筋前减小;此外,钢筋滑移对坝体裂缝分布形态也有一定影响。研究表明:配置坝面钢筋对限制与分散混凝土开裂将起到一定的作用,有助于提高混凝土坝抗震性能。

置换通风的数值模拟

首先介绍了用于数值模拟置换通风室内空气分布的N点风口模型、新零方程湍流模型 ,以简化和加快实际工程中对置换通风的模拟计算。然后利用这些模型对某办公室置换通风的室内温度场和速度场进行了模拟 ,并和实验数据进行对比。结果表明 ,计算所得速度和温度分布与实测值吻合得很好 ,所用的风口模型和湍流模型能将置换通风的温度分层特性和速度场合理地模拟出来 ,可用于指导和优化置换通风气流组织设计。

基于虚拟裂缝模型的混凝土双K断裂参数

本文将虚拟裂缝模型与线弹性断裂力学相结合，利用楔入劈拉试件在实验中测得的最大荷载Ｐｍａｘ及对应的裂缝口张开位移ＣＭＯＤｃ，求得了混凝土裂缝亚临界扩展量Δａｃ的解析解，据此计算了最大尺寸为７００×７００×２００ｍｍ的楔入劈拉混凝土试件的起裂断裂韧度ＫｉｎｉＩｃ、失稳断裂韧度ＫｕｎＩｃ及临界裂缝尖端张开位移ＣＴＯＤｃ，并与试验结果进行了比较．研究结果表明，当试件高度ｈ＞４００ｍｍ时，ＫｉｎｉＩｃ、ＫｕｎＩｃ、ＣＴＯＤｃ是一个与试件高度无关的断裂参数．

多孔介质性质对弱凝胶深部调驱作用的影响

为了克服常规实验装置的不足,明确多孔介质性质对弱凝胶体系深部调驱作用的影响,研究了弱凝胶体系通过玻璃微珠与石英砂填砂模型时的性能及其深部调驱作用的变化。结果表明,动态条件下2种介质中的弱凝胶体系均可发生交联反应,经过水驱后2种介质中的弱凝胶均呈颗粒状。在玻璃微珠模型中,弱凝胶的动态成胶时间较短,生成的弱凝胶均匀分布于整个孔隙空间,残余阻力系数较大,在水驱作用下弱凝胶能够向深部运移并能在深部再次形成封堵,实现其深部调驱作用;而在石英砂填砂模型中,弱凝胶的动态成胶时间较长,生成的弱凝胶主要集中在近入口端,残余阻力系数较小,在水驱作用下弱凝胶能够向深部运移但被剪碎成细小颗粒,不再具有封堵作用,其深部调驱作用较差。多孔介质的剪切破碎作用是影响弱凝胶性质以及降低其深部调驱作用的主要原因。

温度对结构钢材裂纹尖端张开位移(CTOD)的影响分析

裂纹尖端张开位移(CTOD)与钢材的弹性模量、屈服强度、几何条件和荷载大小等因素有关。结构钢材的相关力学指标随着温度发生变化,因此温度变化也会改变CTOD的数值。从含穿透缺口无限大受拉平板的Dugdale-Barrenblett模型(D-B模型)出发,推导出了温度对裂纹尖端张开位移影响规律的基本公式,并把分析进一步扩展到含跨中裂纹的三点弯曲试样。并对带跨中裂纹的三点弯曲试样进行了有限元分析和低温试验,其结果和公式进行了对比。结果表明,CTOD值随着温度降低而减小,温度对CTOD的影响程度与裂纹尖端的塑性发展程度有关。

重力坝断裂数值分析研究

本文研究了预制缝重力坝模型的断裂特性。通过对模型的断裂过程分析表明,在有限元富集技术中引入粘结裂纹模型能够较好地反映模型的承载特性和破坏过程,可以得出与试验结果相一致的荷载响应曲线和裂纹扩展路径。数值方法指出模型试验中采用弹簧拉力计提供附加重力场的局限性。由于拉力计与模型存在联合作用,改变了模型破坏机理和形式,使模型呈现为延性破坏,因而不能反映原型开裂后的实际承载特性。模型试验中附加荷载的施加方式需要改进。