硬质聚氨酯泡沫塑料动态力学性能的研究

介绍了用分离式Ｈｏｐｋｉｎｓｏｎ压杆对硬质聚氨酯泡沫塑料（ＲＰＵＦ）进行的一种高应变率实验,第一次完整地给出了ＲＰＵＦ在１０￣３ｓ￣（－１）高应变率下的动态应力应变曲线,并对ＲＰＵＦ的动态力学性能及其吸能缓冲机理作了简单的分析。     

玻璃纤维增强聚氨酯泡沫塑料的压缩力学性能研究

本文研究了两种不同密度的玻璃纤维增强聚氨酯泡沫塑料在准静态压缩下的力学性能。给出了与相应密度的普通泡沫塑料力学性能的比较,实验结果表明：两种增强泡沫塑料在压缩载荷作用下,具有不同于普通泡沫塑料的应力－应变特性,压缩模量和强度一般均有不同程度的提高,而且对相同纤维含量的增强泡沫塑料来说,密度较高的材料增强效果较好。     

泡沫塑料力学性能研究进展

本文对泡沫塑料力学性能的研究进行了简要综述,重点介绍近期文献和作者在该领域的一些研究工作,及对该领域的研究工作进行展望．     

聚氨酯泡沫塑料在应力波加载下的压缩力学性能研究

通过ＳＨＰＢ冲击实验装置研究了硬质聚氨酯泡沫塑料在应力波加载下的动态力学性能，得到了泡沫塑料在较高应变率下的应力－应变曲线；确定了泡沫塑料的动态屈服强度和动态弹性模量等力学参数，并同落锤冲击实验及准静态压缩实验的结果进行了比较。     

特种泡沫塑料的动态力学性能研究

通过大尺寸分离式Hopkinson压杆对特种泡沫塑料进行了高应变率冲击实验,完整地给出了该材料在高应变率下的动态应力应变曲线,并将结果和理论上的Eyring模型进行了比较,指出了这种材料在一定的应变率范围内,具有明显的应变率效应,同时从应力应变曲线的特点来看,这种材料又有良好的吸能特性,最后通过对实验数据的拟合,提出了便于工程应用的动态本构方程。     

复合泡沫塑料力学行为的研究综述

复合泡沫塑料是一种重要的防护材料,它在国防工业和民用工业各部门均有许多重要的应用,对这类材料的力学行为进行研究具有重要的学术价值和应用前景.本文对复合泡沫塑料力学行为的研究文献进行了综述.首先,对复合泡沫塑料力学行为研究的早期工作进行了简介.然后,重点介绍了复合泡沫塑料力学行为研究的最新进展,其中也包括作者近期在该领域开展的一些工作;对复合泡沫塑料进行了静、动态压缩实验和细观加载实验,研究了材料的宏观变形规律和细观失效机制;在理论研究方面,探讨了复合泡沫塑料的能量吸收和缓冲特性,从宏、细观力学分析出发研究了复合泡沫塑料有关力学性能的理论预测问题;还利用计算机和通用软件对高密度复合泡沫塑料进行了有限元分析,研究了高密度复合泡沫塑料的失效行为.最后,给出对该领域研究工作的一些展望.      

用数字散斑相关法研究聚氨酯泡沫塑料的压缩力学性能

提出了一种改进的数字散班相关计算方法，使其能直接进行应变迭代，灵敏度可达１０００με，并对它进行了验证试验。对于两种不同密度的聚氨酯泡沫塑料，采用改进的数字散斑相关法对其压缩力学性能进行了测试，得到了其应力——应变关系及弹性模量等力学参数。     

聚氨酯泡沫塑料的强度与断裂韧性

针对3种密度的聚氨酯泡沫塑料进行了拉伸实验。通过无缺口试件确定了3种密度泡沫塑料的拉伸断裂强度,而利用有缺口试件确定了这些材料的拉伸断裂韧性。为了研究高密度泡沫塑料的拉伸断裂机制,还对破坏后试件进行了扫描电镜分析。此外,还简要讨论了泡沫塑料拉伸断裂力学性能的理论预测问题。     

胞体椭球比对泡沫塑料力学性能的影响

本文通过数值法研究了胞体椭球比对材料模量及泊松比的影响；在单向受力情况下，研究了变形对材料孔隙度、椭球比、杨氏模量和泊松比等材料参数的影响。     

硬质聚氨酯泡沫塑料本构关系的研究

介绍用大尺寸分离式Ｈｏｐｋｉｎｓｏｎ压杆对四种密度的硬质聚氨酯泡沫塑料进行高应变率实验,完整地给出了这种材料在１０３／ｓ高应变率下的包括弹性区、屈服区和致密区变形全过程的动态应力应变曲线,并提出了包括应力、应变、应变率和密度等参量的本构关系．     

Multiaxial yield behaviour of Al replicated foam

Multiaxial experiments are performed on replicated aluminium foam using a custom-built apparatus. The foam structure is isotropic, and features open monomodal pores in average diameter. Plane stress (σ₁, σ₂, σ₃=0) and axisymmetric (σ₁, σ₂=σ₃) yield envelopes are measured using cubical specimens, supplemented by tests on hollow cylindrical and uniaxial samples. In addition to the three stress components at 0.2% offset strain, the computer-controlled testing apparatus also measures the three instantaneous displacement vectors.Results show that the shape of the yield surface is independent of the relative density of the foam in the explored range (13-28%). Strain increment vectors lie, within error, roughly normal to the line traced through data points in stress space. Replicated foams feature asymmetric yield behaviour between tension and compression. The data additionally show an influence on the yield surface of the third stress tensor invariant (i.e., of the Lode angle). Simple general expressions for the yield surface are fitted to the data, leading to conclude that their behaviour is slightly better captured by parabolic rather than elliptic expressions dependent on all three stress invariants.     

山东龙口北皂煤矿软岩力学特性实验研究

根据室内实验结果, 本文讨论了北皂煤矿的岩石力学性质, 物化特性。泥质岩类的力学性质和水理性质、物化特性有关。泥质岩类具有显著的流动变形和各向异性。     

Shape and size effects of ceria nanoparticles on the impact strength of ceria/epoxy resin composites

Ceria nanoparticles with various shapes (rods, cubes, and plates) and sizes were controllably synthesized and then introduced into epoxy resin. Subsequently, we investigated correlations between the shape and size of ceria nanostructures and the mechanical performance of composites. The samples were characterized by transmission electron microscopy, scanning electron microscopy, and X-ray diffraction. Compared with commercial ceria filled composites, the composites made with morphology-controlled ceria nano...     

Effects of size on the strength and deformation mechanism in Zr-based metallic glasses

We report results of uniaxial compression tests on Zr₃₅Ti₃₀Co₆Be₂₉ metallic glass nano-pillars with diameters ranging from ∼1.6 μm to ∼100 nm. The tested pillars have nearly vertical sidewalls, with the tapering angle lower than ∼1° (diameter >200 nm) or ∼2° (diameter ∼100 nm), and with a flat pillar top to minimize the artifacts due to imperfect geometry. We report that highly-localized-to-homogeneous deformation mode change occurs at 100 nm diameter, without any change in the yield strength. We also find that yield strength depends on size only down to 800 nm, below which it remains at its maximum value of 2.6 GPa. Quantitative Weibull analysis suggests that the increase in strength cannot be solely attributed to the lower probability of having weak flaws in small samples - most likely there is an additional influence of the sample size on the plastic deformation mechanism.     

On the uniqueness of measuring elastoplastic properties from indentation: The indistinguishable mystical materials

Indentation is widely used to extract material elastoplastic properties from the measured force-displacement curves. One of the most well-established indentation techniques utilizes dual (or plural) sharp indenters (which have different apex angles) to deduce key parameters such as the elastic modulus, yield stress, and work-hardening exponent for materials that obey the power-law constitutive relationship. However, the uniqueness of such analysis is not yet systematically studied or challenged. Here we show the existence of “mystical materials”, which have distinct elastoplastic properties yet they yield almost identical indentation behaviors, even when the indenter angle is varied in a large range. These mystical materials are, therefore, indistinguishable by many existing indentation analyses unless extreme (and often impractical) indenter angles are used. Explicit procedures of deriving these mystical materials are established, and the general characteristics of the mystical materials are discussed. In many cases, for a given indenter angle range, a material would have infinite numbers of mystical siblings, and the existence maps of the mystical materials are also obtained. Furthermore, we propose two alternative techniques to effectively distinguish these mystical materials. The study in this paper addresses the important question of the uniqueness of indentation test, as well as providing useful guidelines to properly use the indentation technique to measure material elastoplastic properties.     

聚氨酯泡沫塑料动态剪切力学行为的研究

通过大型精密分段式Ｈｏｐｋｉｎｓｏｎ 扭杆实验装置对聚氨酯泡沫塑料进行了动态扭转实验,研究了聚氨酯泡沫塑料在剪切应力波加载下的力学行为,得到了这类材料的动态剪切应力 应变曲线和动态力学性能参数。此外,针对动态扭转破坏试件断口进行了扫描电镜分析,研究了泡沫塑料动态剪切破坏的机制。还给出了同准静态扭转实验结果的比较。     

Influence of thermal aging on tensile and creep behavior of thermoplastic polyurethane

Changes in mechanical and physical properties of polyurethane thermoplastic during aging at 70 °C and 90 °C were investigated. The loss weight response was analyzed by gravimetric measurements under these temperatures. Changes in appearance and morphology of TPU after thermal aging were revealed by optical microscopy. The prolongation of the thermal exposure time, up to 270 days, leads to a progressive increase in tensile strength. In fact, elastic modulus and stress at 200% of strain were increased with thermal exposure time. These results can be explained by the increase of thermal stability due to the increase of material rigidity and the decrease in chain mobility. The evolution of the mechanical properties from tensile tests seems to be well correlated to the creep behavior. Finally, Scanning Electron Microscopy (SEM) revealed the modification of TPU morphology fracture surface after thermal aging.     

Modeling oxidation damage of continuous fiber reinforced ceramic matrix composites

For fiber reinforced ceramic matrix composites(CMCs),oxidation of the constituents is a very important damage type for high temperature applications. During the oxidizing process,the pyrolytic carbon interphase gradually recesses from the crack site in the axial direction of the fiber into the interior of the material. Carbon fiber usually presents notch-like or local neck-shrink oxidation phenomenon,causing strength degradation. But,the reason for SiC fiber degradation is the aw growth mechanism on its surface. A micromechanical model based on the above mechanisms was established to simulate the mechanical properties of CMCs after high temperature oxidation. The statistic and shearlag theory were applied and the calculation expressions for retained tensile modulus and strength were deduced,respectively. Meanwhile,the interphase recession and fiber strength degradation were considered. And then,the model was validated by application to a C/SiC composite.