Behavior of two parallel symmetry permeable cracks in functionally graded piezoelectric materials subjected to an anti-plane shear loading

The behavior of two parallel symmetry permeable cracks in functionally graded piezoelectric materials subjected to an anti-plane shear loading was investigated. To make the analysis tractable, it was assumed that the material properties varied exponentially with coordinate vertical to the crack. By using the Fourier transform, the problem could be solved with the help of two pairs of dual integral equations, in which the unknown variables were the jumps of the displacements across the crack surfaces. To solve the dual integral equations, the displacement on the crack surfaces was expanded in a series of Jacobi polynomials. The normalized stress and electrical displacement intensity factors were determined for different geometric and property parameters for permeable electric boundary conditions. Numerical examples were provided to show the effect of the geometry of the interacting cracks and the functionally graded material parameter upon the stress intensity factors of cracks.     

The non-local theory solution of a Griffith crack in functionally graded materials subjected to the harmonic anti-plane shear waves

In this paper, the dynamic stress field near crack tips in the functionally graded materials subjected to the harmonic anti-plane shear stress waves was investi- gated by means of the non-local theory. The traditional concepts of the non-local theory were extended to solve the fracture problem of functionally graded materials. To make the analysis tractable, it was assumed that the material properties vary exponentially with coordinate parallel to the crack. By use of the Fourier transform, the problem can be solved with the help of a pair of dual integral equations, in which the unknown variable was the displacement on the crack surfaces. To solve the dual integral equations, the displacement on the crack surfaces was expanded in a series of Jacobi polynomials. Unlike the classical elasticity solutions, it is found that no stress singularities are present at crack tips. The non-local elastic solutions yield a finite hoop stress at crack tips, thus allowing us to use the maximum stress as a fracture criterion. The magnitude of the finite dynamic stress field depends on the crack length, the parameter describing the functionally graded materials, the circular frequency of the incident waves and the lattice parameter of materials.     

短纤维增强复合材料动态剪切模量及热膨胀系数预报

为了加强对短纤维增强复合材料的细观动态及热失配性能预报,利用Eshelby等效夹杂理论,通过三参数粘弹性本构模型,研究了Glass/ED6短纤维增强复合材料的粘弹性响应机理,并对该材料动态剪切模量及碳/环氧材料热膨胀系数随温度变化的规律进行了预报.结果表明,材料的剪切模量与组分间的体积分数以及加载频率间联系紧密,有效热膨胀系数与温度密切相关.通过曲线可以发现,当加载频率值较高时,动态剪切模量主要由实部决定;而当纤维的体积分数较大时,动态剪切模量的变化主要由虚部决定,这将使材料力学性能计算过程得到简化.针对碳/环氧材料,通过研究发现随着温差的增大,材料的热膨胀系数随之下降.     

压磁-压电复合材料的磁电-力学行为研究进展

压磁-压电复合材料是一种新型的多功能材料,兼具压电性和压磁性,磁电耦合效应远高于单相材料。综述了磁电复合材料的磁电-力学行为与特征,主要分析方法包括等效电路法、格林函数法、有限元分析法和状态空间法,并讨论了磁电复合材料中的缺陷影响。     

基于积分法的热非平衡效应下剪切液膜流的表面波演化模型

当液膜表面同时存在热非平衡效应和切应力作用时,引发液膜流动不稳定的扰动及其影响将更为复杂。基于边界层理论,通过建立气液界面受热非平衡效应和切应力耦合作用的液膜流动的理论模型,采用包含弱非线性项的积分法,推导出热非平衡效应下剪切液膜流的表面波积分演化模型,模型中包括了相变强度、切应力、雷诺数和倾斜角度等不同参数的影响,为分析复杂边界条件下的液膜流的演化特征和稳定性提供了一种可借鉴的理论模型。     

简谐正弦磁压力对电磁发射轨道的瞬态响应

为解决电磁发射轨道发射精度不够高及炮筒使用年限不够长的难题,将电磁炮发射轨道模拟为移动载荷作用下弹性基础上的简支梁,利用欧拉梁理论建立了梁的力学模型;借助积分变换及逆变换和计算留数等方法,推导出简谐压力作用下轨道梁瞬态响应解析解;借助MATLAB软件分析了粘滞外阻尼系数、摩擦阻尼系数、弹性系数对梁的瞬态动力响应的影响。计算分析表明:轨道梁的挠度随黏滞外阻尼系数的增大而减小;随着材料应变阻尼系数的增大而增大;而弹性系数对挠度的影响不太明显,挠度曲线随着弹性系数的增加而呈下降的趋势。     

具有常规原因和人为错误的两个不同部件并联系统解的半离散化

讨论了一个由于常规原因和人为错误引起故障的两不同部件并行系统的模型,修复后的故障系统恢复正常。在假设修复率非常数的前提下,运用半群理论证明了系统解的存在唯一性,最后对修复率用初等阶梯函数逼近给出了系统半离散化模型,为进一步数值计算奠定了理论基础。     

无限长条功能梯度材料的反平面裂纹问题

研究了无限长条正交各向异性功能梯度材料在平面剪切作用下的Yoffe裂纹的动力学问题，材料的两上方向的剪切模量假定为指数模型，通过采用积分变换-积分方程方法，求得了裂纹尖端的动态应力场和动态应力强度因子，并研究了裂纹运动速度、几何尺寸、梯度参数和不均匀系数对动态应力强度因子的影响，结果表明，裂纹尖端应力具有的奇异性，裂纹的运动速度越大，应力强度因子越大；材料的模量梯度越大，应力强度因子越低；不均匀系数越大，应力强度因子越小。     

住宅屋面裂缝的产生与防治

通过分析工程实例中屋面裂缝的处理，对屋面裂缝产生的原因，治理及预防措施进行阐述，就防止产生屋面裂缝及相应处理方法与广大设计，施工人员进行探讨。     

The Deformation Behavior of TiNi Shape Memory Alloy under Axial Dynamic Compression

The deformation behavior of Ti-50.9at% Ni shape memory alloy under axial compression dynamic loads was investigated by an MTS 858Miru Bionic test machine. The alloy were aged at 500℃ for an hour before being machined into specimens. The compression experiments were conducted at 20℃ and the variety of dynomic loads were controlled by the strain rate, which was 3mm/min, 15mm/min, 30mm/min and 50mm/min, respectively. The experimental results indicate that in the case of 3mm/min. stress-induced martensitic transformation occurs at about 350 MPa when loading and reverse transformation at about 200 MPa when unloading, during which the aged Ti-50.9at% Ni alloy shows the recoverable nonlinear pseudoelastic strain of 4.3%with the residual strain of 1.2% reserved. With the strain rate increasing, the area encloses by loading-curve and unloading-curve, i. e stress ( strain ) hysteresis becomes smaller and smaller and the residual strain also decreases, while critical stress for inducing martensitic transformation rises. At a higher strain rate the alloy exhibits linear-like pseudoelasticity, which is up to 4.5％ .     

The effect of applied stress on damage mode of 3D C/C composites under bend-bend fatigue loading

The bend-bend fatigue behavior of 3D integral braided carbon/carbon composites (3D C/C) was examined. Fatigue test was conducted under load control at a sinu-soidal frequency of 10 Hz to obtain stress-fracture cycles (S-N) relationship. The fatigue limit of the C/C was found to be 203 MPa (92% of the static flexural strength), the lag loops of fatigue load-displacement were transformed from elasticity to anelasticity and the flexibility of specimens were enhanced with increase in applied stress. It is revealed that the interfacial sliding abrasion played an important role in the fatigue failure process, and the extent and speed of sliding abrasion were con-trolled by the level of applied stress.     

连续梁、连续刚构桥施工中腹板产生裂缝的机理及对策

随着连续梁和连续刚构桥的广泛应用,一些桥梁在施工过程中腹板出现裂缝.本文以弹性力学为依据,运用Ansys建立连续梁、连续剐构桥三维实体模型,计算混凝土腹板三向受力情况下的主拉应力,并对比腹板内最大主拉应力与混凝土抗拉强度的关系,由此说明腹板产生裂缝的原因.结合实际桥梁,计算悬臂现浇法施工时四种工况下混凝土腹板应力,得出最大主拉应力为:0.67 MPa、0.32 MPa、2.76 MPa和0.98 MPa.由此说明竖向预应力能有效控制腹板混凝土的主拉应力,即为了预防混凝土腹板内部主拉应力超过混凝土抗拉强度,应在施工时先张拉竖向预应力,再张拉纵向预应力钢筋.     

两个风险模型的生存概率的积分方程

经典风险模型中,保费收入是时间的线性函数．双泊松风险模型中,保费收入过程是一泊松过程．给出了这两个风险模型下各自的生存概率所满足的积分方程．基于后一种风险模型,在一个无穷小的时间区间内,根据理赔的次数和收取保单的次数,应用全概率公式,得出了相应的积分方程．     

形状记忆合金的动力响应特性及振动控制

通过对形状记忆合金（ＳＭＡ）材料基本性能的试验研究，提出了ＳＭＡ的相变伪弹性恢复力模型，并以此为基础研究了ＳＭＡ减振控制系统的动力响应问题．模拟结果表明这种减振控制装置对较强烈的振动有更好的抑制作用，并且控制其温度即可使系统处于最佳工作状态．     

风、波、流联合作用下的浅海域隔水导管屈曲仿真

在对隔水导管进行受力分析的基础上,拟合出风、波、流载荷随高度和深度变化的函数关系式。以某浅海油田工程为例,联合风、波、流的共同作用力,采用Workbench模拟导隔水管在最恶劣工况下屈曲响应和应力分布,得出隔水导管的临界失稳载荷与形变特点以及应力分布,指出结构薄弱环节;根据所得固有频率,算得各阶频率所对应共振转速。