单个薄壁多孔金属空心球体力学行为研究

金属空心球多胞材料结构是一种新型的多孔金属材料,它是由多个金属空心球组合而成,对于单个金属空心球的力学行为研究是整体材料力学性能的基础。通过对外径2 mm～3 mm,且壁厚不等厚(壁厚10μm～40μm)的单个超薄壁多孔空心球体进行纳米压痕试验、准静态单轴压缩试验以及纯弹性阶段的压缩试验,进而得到该金属空心球体材料和整个球体的弹性模量等相关力学参数,以及金属空心球体压缩变形过程和特征,并对金属空心球体弹性阶段采用有限元软件Abaqus进行模拟,分析孔隙率对于球体弹性模量的影响,结果表明,随着球壁孔隙率的增大,球体的弹性模量减小,且呈非线性分布,并可以描述成与球壁孔隙率与球壁材料的力学性能关系相同的幂函数形式。     

薄壁金属球壳及其组元压缩大变形研究

对薄壁金属球壳及组元模型(SC(square cumulation)、HC(hexagonal cumulation)和FC(face-centered cumulation)三种组元模型)进行大变形压缩研究,分别得出各自的压缩力学性能:单个球壳受单轴压缩其名义应力应变关系初始为线性,然后会出现两次局部屈曲,在变形过大时会发生非轴对称变形;SC、HC和FC三种组元模型压缩名义应力、应变关系初始也呈线性,然后趋于平缓,其中SC和HC组元发生了非对称变形,而FC组元发生了对称变形;得出各自的名义弹性模量和屈服极限。以上内容对空心球基多胞材料的研究和应用具有参考意义。     

煤矸石空心球多孔材料的制备及性能研究

以煤矸石空心球和玻璃粉为主要原料,加入发泡剂碳酸钙(Ca CO3)及其他辅助添加剂,采用化学发泡法,经低温烧结成功制备煤矸石空心球多孔陶瓷材料,并对其性能进行研究。结果表明,随着烧结温度的升高,样品的表观密度明显下降,当烧结温度为670℃时所制备样品的表观密度已降低为190 kg/m3;多孔陶瓷材料的孔径随着烧结温度升高逐渐增大,样品的平均体积吸水率呈现先降低后小幅度升高的变化趋势;同时,表观密度对热导率影响很大,当试样表观密度为520 kg/m3时,其热导率为0.103 W/(m·K),随着试样表观密度的降低,其热导率呈明显的下降趋势,试样表观密度减小到190 kg/m3时,其热导率降至0.037 W/(m·K);以煤矸石为原料制得性能优异的多孔材料,为煤矸石的综合利用开辟了一个新的途径,具有显著的环境效益、经济效益和社会效益。     

大长径比薄壁燃烧室壳体加工变形分析与控制技术研究

固体火箭发动机壳体的保形加工是航天装备制造的重要环节。可靠的整形工装是控制加工变形和降低尺寸偏差的前提。通过对壳体制造、装药制造及装配等过程的系统测量与分析,明确了壳体在制造过程中产生变形的基本规律。基于有限元仿真分析方法,提出了焊接变形、热处理变形的分析与控制策略。分析表明,热处理过程中的组织场和应力场变化是造成壳体变形的主要因素,通过改善工装底部支撑梁结构可以达到控制变形的目的。通过试验分析优化后工装的变形量可知,试验结果与仿真规律一致。因此,将工装底部支撑梁改为格栅式导流板后气场流动更稳定,且一次回火+整形工装对抑制壳体变形效果显著。     

多孔Cu-Ni-Al合金的高温压缩变形行为及本构关系

采用雾化法制备Cu-Ni-Al粉末,对其进行真空热压烧结制取多孔Cu-Ni-Al合金,研究该材料的微观组织、高温压缩变形行为及其影响因素,分析压缩变形机理。结果表明,多孔Cu合金的抗压强度、弹性模量以及屈服强度随着变形温度的增加、应变速率的减小而减小;多孔Cu合金的压缩变形过程分为初始的线性弹性变形、孔壁的塑性变形、弯曲或断裂的屈服平台区以及孔洞密实化后的塑性变形三个阶段;在高温压缩变形过程中,多孔Cu合金容易在孔洞比较集中,孔壁较薄的地带出现应力集中,发生变形。采用回归分析方法建立多孔Cu合金的高温压缩变形本构方程,得出的计算曲线与试验曲线在压缩变形的第一、二阶段非常吻合,在第三阶段,计算曲线稍微高于试验曲线,分析原因认为可能是多孔Cu合金中的孔隙分布不均有关。     

纸浆模塑材料压缩力学行为及其本构关系的研究

对纸浆模塑材料的压缩力学行为进行较系统的实验研究,结果表明材料密度和应变率都对其力学性能有一定的影响.随着材料密度的增加,其弹性模量和强度极限都有增加的趋势.随着应变率的增加,其材料的弹性模量有减小的趋势,而强度极限有所增大.利用描述泡沫塑料的经验型本构关系框架,给出一种经验型的纸浆模塑材料本构模型,根据不同密度材料在不同应变率下的压缩实验数据对该模型中的有关系数进行拟合.验证结果表明,提出的本构方程能在一定应变率范围内反映材料的应力-应变关系.     

腹板开孔薄壁工字梁准静态压缩力学行为及稳定性分析

对蜂窝、内凹和椭圆构型腹板开孔薄壁工字梁在准静态单轴压缩作用下的力学行为及稳定性进行了实验和有限元仿真研究。通过对比实验和有限元仿真的结果,验证有限元仿真的可靠性。基于实验结果和有限元仿真结果,分析了不同构型腹板开孔薄壁工字梁的最大承载力、弹性模量和破坏机制,得出孔型对腹板开孔薄壁工字梁压缩失稳的影响规律。研究表明,孔到翼缘的距离越大结构稳定性越好,稳定性较好的腹板开孔薄壁工字梁压缩失稳的位置出现在两孔之间,同时内凹构型相比蜂窝和椭圆构型腹板开孔薄壁工字梁具有更好的稳定性。     

静电陀螺仪空心球形转子的动态变形分析

本文利用有限元分析软件,对静电陀螺仪空心球形转子进行了离心变形的计算及变形仿真,同时考虑了加工误差造成的不对称转子的离心变形,讨论了不同结构转子的动态变形以及对圆球度误差的影响,提出了减小和补偿圆球度误差的措施.     

大型薄壁硬质铝合金零件加工技术研究

以某火炮左、右组合炮箱为例,分析高强度硬质铝合金薄壁零件的加工特点,通过优化工艺路线和加工方法,运用分层铣削法加工毛坯,利用交叉分层铣削法减少零件应力变形,采用刨削法保证大面平面度要求,将左、右箱体板耦合加工各孔,保证孔的位置度要求。结果表明,该加工方法可有效提高零件的加工质量和加工效率,对控制薄板类零件加工应力变形有一定的借鉴意义。     

薄壁注塑件翘曲的正交分析及优化

分析了注塑制件翘曲的原因,采用著名的CAE软件Moldnow与正交试验方法,对不同工艺条件下的注塑成型过程进行模拟分析并对正交实验数据进行极差分析,确定注射时间、保压压力、保压时间、冷却时间、熔体温度、模具温度以及冷却液温度等注塑成型工艺参数对制件翘曲变形的影响程度,得出最优的注塑成型工艺参数组合,并以一薄壁导光板对该工艺组合方案进行模拟验证与实际注塑实验验证。     

Impact behaviour of hollow sphere agglomerates with density gradient

This paper presents a study on the influence of the density gradient profile on the mechanical response of graded polymeric hollow sphere agglomerates under impact loading. Quasi-static, standard split Hopkinson pressure bar (SHPB) tests as well as higher speed direct impact Hopkinson bar tests and Taylor tests are performed on such hollow sphere agglomerates with various density gradient profiles. It is found that the density gradient profile has a rather limited effect on the energy absorption capacity from those tests. It is because the testing velocity performed (<50 m/s) is rather small with respect to its average sound wave speed (around 500 m/s) and the equilibrium stress state can be reached rather quickly. The high impact tests allow to generate a non-equilibrium state condition and the influence of density profiles is clearly observed. Besides, in order to extend this study to the situation beyond our testing limitations, a numerical model is built on the basis of the experimental behaviour data. It confirms the important influence of the density gradient profile under a non-equilibrium stress state situation. This study shows that placing the hardest layer as the first impacted layer and the weakest layer as the last layer has some benefits in terms of maximum energy absorption with a minimum force level transmitted to the protected structures.     

Modelling of MHS cellular solid in large strains

The stress–strain characteristics of metal hollow sphere (MHS) material are obtained in relatively large strains under uniaxial compression in two characteristic loading directions. Based on the hypothesis of periodic repeatability of a representative block, large deformations of the material are modelled when assuming point connections between the spheres. The elastic deformations are neglected and a rigid perfectly plastic model is assumed for the base material. A structural approach using the limit analysis and the concept of an equivalent structure are then employed to describe the large plastic deformations during post-collapse process of metal hollow spheres, which undergo mainly a snap-through deformation. Stress vs. material density relationships are proposed for different strain levels in each direction of loading. The obtained results can be used to estimate the energy absorbing capacity of MHS materials under quasi-static loading. The theoretical predictions are compared with some test results and reasonable agreement is shown.     

Large deformation pure bending of an elastic plastic power-law-hardening wide plate: Analysis and application

The large deformation pure bending of a wide plate made of a power-law-hardening material is solved. The deformation theory, the flow theory with either isotropic hardening or kinematic hardening, and the shell theory (which ignores the transverse stress) have been used in the respective analyses and their results have been compared. The solutions reveal that large curvature bending can result in a significant thickness reduction of the bent plate, and therefore the non-dimensional bending moment initially increases with the non-dimensional bending curvature, reaches a peak point, and then drops with the further increment of the non-dimensional bending curvature. When a metallic honeycomb is in-plane crushed, the maximum non-dimensional bending curvature in the cell walls (plates) can well exceed 1.5, the external energy is mainly absorbed by the plastic-hinges whose size is within the order of the cell wall (plate) thickness.     

Shear deformable doubly- and mono-symmetric composite I-beams

A shear deformable beam element is developed for the coupled flexural and torsional analyses of thin-walled composite I-beams with doubly- and mono-symmetric cross-sections. The present element includes the transverse shear and the restrained warping induced shear deformation by using the first-order shear deformation beam theory. Governing equations and force-displacement relations are derived from the principle of minimum total potential energy. Then the explicit expressions for displacement parameters are derived by applying the power series expansions of displacement components to simultaneous ordinary differential equations. Finally, the element stiffness matrix is determined using the force-displacement relations. In order to verify the accuracy and the superiority of the beam element developed herein, the numerical solutions are presented and compared with the results obtained from the isoparametric beam elements based on the Lagrangian interpolation polynomial, the detailed three-dimensional analysis results using the shell elements of ABAQUS, and the solutions by other researchers.     

Preparation and tribological properties of tungsten disulfide hollow spheres assisted by methyltrioctylammonium chloride

In the current paper, tungsten disulfide hollow spheres modified by methyltrioctylammonium chloride with diameters of about 200 nm have been successfully prepared through a solvothermal process. The products were characterized by X-ray power diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, scan electron microscopy and high revolution transmission electron microscopy, respectively. The tribological properties of the as-prepared WS₂ in liquid paraffin (LP) were studied and compared with those of commercial colloidal MoS₂ (CC-MoS₂). The worn surfaces were analyzed by XPS and SEM. Results show that the as-prepared WS₂ hollow sphere is a better anti-wear and friction-reducing additive in LP than CC-MoS₂.     

轿车密封条压缩变形的基础性能研究

开发研制新型密封条压缩过程的力－位移动态测试装置,通过计算机控制,可以实现不同压缩速度下的力－位移响应特征测试。该装置不仅能够评价各种密封条结构对车门关闭力的影响,同时也为采用Ｍａｒｃ等ＣＡＥ分析软件进行密封条结构设计和优化奠定了基础。     

Modelling fatigue damage accumulation in two-dimensional Voronoi honeycombs

Trabecular bone, a porous, cellular type of bone found at the ends of the long bones and within the vertebrae, is subject to cyclic compressive loading resulting from the activities of daily living. Such fatigue loading can result in fracture, especially in vertebrae of patients with osteoporosis. As an initial step in understanding compressive fatigue of trabecular bone we previously used finite-element analysis to model the progressive damage and failure of a simple, two-dimensional hexagonal honeycomb. In this study, the analysis is extended to a random, Voronoi honeycomb. Bending of the cell walls induces tensile stresses even when the overall loading is compressive. The cell walls are assumed to have a distribution of crack lengths in their tensile zones. The cracks are assumed to grow according to a Paris law and fail when the cracks reach 75% of the cell wall thickness. Failed cell walls are removed from the structure, the stress distribution recalculated and the next increment of fatigue loading are simulated. The Young's modulus of the honeycomb is calculated after each cell wall failure. Overall failure of the Voronoi structure is assumed to occur when the modulus is reduced by 5%; further loading reduces the modulus sharply. The slope of the S–N curve for the Voronoi honeycomb is the same as that for the hexagonal honeycomb. The model suggests that a random honeycomb is more sensitive to fatigue than a regular one.     

Large deformation compression–torsion behaviour of a titanium alloy and its modelling

A range of sequential and compound compression-torsion tests has been carried out on titanium alloy IMI834 at 1000°C and nominal true strain rate 5 × 10⁻³ s⁻¹, typical of forging conditions. The tests were used to investigate initial and subsequent yield and flow behaviour, the nature of the material hardening and the effect of flow softening on subsequent deformation. In addition, a material model with isotropic or directional hardening has been used to predict the material behaviour.The results show that the material behaviour at large strains is reasonably isotropic, although a directional hardening model provides slightly better quantitative agreement with the experimental results. Large pre-strains (0.4), either axial or torsional, are found not to change significantly subsequent material behaviour. A stress state dependence of flow softening is observed to exist.The material model presented is shown to give good quantitative agreement of predicted and experimental results.