强激光输出窗口热行为对光束质量的影响

为了研究强激光输出窗口热行为对光束质量的影响,从Strehl比的普遍公式出发,推导出热变形情况下考虑材料折射率温度效应的Strehl比计算公式和远场强度分布公式。计算并分析了蓝宝石、石英、单晶硅组成的窗口镜的热变形对光束质量的影响。激光功率越高,引起的窗口的热变形越显著,使得Strehl比和远场归一化强度越低,因而光束质量越差;在考虑到材料折射率的温度效应时,在相同的激光辐射条件下,蓝宝石的Strehl比随激光功率的变化较平缓。结果表明,高功率激光器的窗口热变形及其基片材料折射率的温度效应对远场光束质量具有较大的影响。     

立式圆筒形钢制储罐焊接变形在焊接上的控制

根据立式钢制储罐在焊接过程中产生焊接变形的现象,分析了焊接变形的原因,提出了控制焊接中罐板变形的措施,以有效保证工程施工中的焊接质量和罐体制作质量。     

组合楼板的全过程挠度分析

对组合楼板的挠度进行研究,其值直接取决于异性钢板与混凝土间连接的剪切刚度。基于架构理论,直接考虑连接的剪切刚度,提出计算组合楼板挠度的方法,考虑混凝土层在普通裂缝和受压下塑性变形对结构刚度的影响。采用本方法,可获得这些影响因素从初始阶段至极限状态全范围的变化情况。对异形钢板与混凝土的连接试件进行试验,结果表明:其连接性能分3个阶段。每个阶段都有不同的剪切特性,用于计算楼板挠度。从加载初期至极限状态,分析Holorib异形板组合楼板变形试验值的变化。采用本方法计算的楼板变形值与试验值吻合较好。     

钛合金加工特性分析及刀具选择

钛合金因其性能的优越性,在航空、航天、石油、化工、汽车和核武器事业等生产领域得到了广泛的应用,但在数控加工钛合金过程中,存在切削效率低下、刀具耐磨性差、切削排屑困难等加工难题.本文通过多次加工试验和研究,总结出了一套加工钛合金的方法,取得了较为理想的切削效果.     

A nonlinear magnetoelastic tube under extension and inflation in an axial magnetic field: numerical solution

In the context of nonlinear magnetoelasticity theory very few boundary-value problems have been solved. The main problem that arises when a magnetic field is present, as compared with the purely elastic situation, is the difficulty of meeting the magnetic boundary conditions for bodies with finite geometry. In general, the extent of the edge effects is unknown a priori, and this makes it difficult to interpret experimental results in relation to the theory. However, it is important to make the connection between theory and experiment in order to develop forms of the magnetoelastic constitutive law that are capable of correlating with the data and can be used for making quantitative predictions. In this paper the basic problem of a circular cylindrical tube of finite length that is deformed by a combination of axial compression (or extension) and radial expansion (or contraction) and then subjected to an axial magnetic field is examined. Such a field cannot be uniform throughout, since the boundary conditions on the ends and the lateral surfaces of the tube would be incompatible in such circumstances. The resulting axisymmetric boundary-value problem is formulated and then solved numerically for the case (for simplicity of illustration) in which the deformation is not altered by the application of the magnetic field. The distribution of the magnetic-field components throughout the body and the surrounding space is determined in order to quantify the extent of the edge effects for both extension and compression of the tube.     

Some numerical simulations of large deformations of heterogeneous hyperelastic media

Numerical experiments done on a two-dimensional stratified two-phase composite corroborate theoretical results on homogeneization of media capable of large deformations.     

Effective behaviour of elastic heterogeneous thin structures at finite deformations

In this contribution the effective material behaviour of thin structures like membranes and plates consisting of heterogeneities is investigated. The diameter of typical inclusions can be in the order of magnitude of the thickness of the membrane or plate. Thus, the prerequisite for a standard homogenization procedure using representative volume elements is not fulfilled anymore, since the required size of an RVE would be larger than the thickness of the structure itself. Additionally the assumption of uniformity of the boundary conditions on the RVE would be violated especially for plates since in general the predominant deformation of such structures is bending. However, it can be shown that the effective behaviour of such heterogeneous thin structures subjected to finite deformations is still in good agreement to the results obtained for homogenized materials.     

Three-dimensional crack initiation, propagation, branching and junction in non-linear materials by an extended meshfree method without asymptotic enrichment

This paper presents a three-dimensional, extrinsically enriched meshfree method for initiation, branching, growth and coalescence of an arbitrary number of cracks in non-linear solids including large deformations, for statics and dynamics. The novelty of the methodology is that only an extrinsic discontinuous enrichment and no near-tip enrichment is required. Instead, a Lagrange multiplier field is added along the crack front to close the crack. This decreases the computational cost and removes difficulties involved with a branch enrichment. The results are compared to experimental data, and other simulations from the literature to show the robustness and accuracy of the method.     

Large deformations and stability in topology optimization

The present contribution focuses on the influence of geometrical nonlinearities on the structural behavior in the design process. The notion of the stiffest structure loses its clear definition in the case of nonlinear kinematics; here we will discuss this concept on the basis of different objectives. Apparently topology optimization is often a generator of slender struts, which tend to buckle before the structure is completely loaded. To include the instability phenomena into the design process, the critical load level will be determined directly; this condition will be included as an inequality constraint. Further on, to reduce the imperfection sensitivity, a geometrically modified structure including the imperfection shape is also introduced. The present optimization procedures are demonstrated by examples showing rather the principal effects of the enhancements than real practical design problems.     

Grid_strain and grid_strain3: Software packages for strain field computation in 2D and 3D environments

Two Matlab™ software packages for strain field computation, starting from displacements of experimental points (EPs), are here presented. In particular, grid_strain estimates the strain on the nodes of a regular planar grid, whereas grid_strain3 operates on the points of a digital terrain model (DTM). In both cases, the computations are performed in a modified least-square approach, emphasizing the effects of nearest points. This approach allows users to operate at different scales of analysis by introducing a scale factor to reduce or also exclude points too far from grid nodes. The input data are displacements (or velocities) that can be provided by several techniques (e.g. GPS, total topographical station, terrestrial laser scanner). The analysis can be applied to both regional- and local-scale phenomena, to study tectonic crustal deformations (strain ≈10⁻⁸−10⁻⁶) or rapid landslide collapses (10⁻⁴−10²), and to characterize the kinematics of the studied system. Errors on strains and geometric significance of the results are also provided.