Split Hopkinson pressure bar (SHPB) technique is used to determine the dynamic strength of reactive powder concretes (RPCs) with different steel-fiber contents. Two types of pulse shapers with different thicknesses are considered to reduce the high-frequency-oscillation effect and achieve a nearly constant strain rate over a certain deformation range. It is known that the compressive strength of concrete-like materials is hydrostatic-stress-dependent, and the apparent dynamic strength enhancement comes from both the effects of the hydrostatic stress and strain rate. In order to differentiate them, numerical method is used to calculate the contribution of the hydrostatic stress, and then the genuine strain-rate effect on dynamic compressive strength of RPCs is determined. In addition, the effect of steel-fibers on dynamic strength and failure mode of RPCs is discussed.

借鉴聚合物结晶学相关理论，建立了一个针对该类材料的新的热力学本构关系，通过与已有实验结果相比较，发现理论预测值与实验吻合较好。

Elasticmemorycomposites (EMCs) are receivingmore attention in deployable spacecraft industry because they can realizemuch higher packaging strains without damage and automatically recover to their original shapes when subjected to a specific thermomechanical cycle. Experimental researches have revealed that microbuckling and post-microbuckling responses of compressed fibers in the soft matrix are the primary deformationmechanism ofEMCsto realize higher packaging strains than traditionalcomposites.However, a thorough understanding about the deformation mechanism of EMCs has not yet been achieved. This paper presents a new shear/tension microbuckling solution to study the deformation and failure process of EMC laminates under bending. The microbucklingwavelength, critical compressive stress and strain for carbon-fiber/resin EMC laminates are calculated, and different theoretical solutions are compared with the experimental observation. Moreover, the possible failure modes of this type of materials arediscussed as well.

通过对活性粉末混凝土材料进行Hopkinson压杆冲击压缩实验，得到不同钢纤维含量的活性粉末混凝土在不同应变率下的应力-应变全曲线，并给出了不同应变率下材料的动态压缩强度和动态增长因子，实验结果表明，活性粉末混凝土具有应变率敏感性，钢纤维的掺入部分提高了材料的冲击压缩性能。

In this paper, the viscoelastic behavior of PI/SiO2 nanocomposite thin films under constant and fatigue tensile loading was studied. The cyclic hardening and viscous dissipation of PI/SiO2 nanocomposite thin films during the fatigue process were experimentally investigated and analyzed by storage modulus, loss modulus and phase lag. The time-dependent deformation under constant and fatigue loading was simulated based on two viscoelastic models known as Burger model and Findley power law. Standard parameter analysis methodology was employed to interpret the structure–property relationship and deformation mechanisms of this kind of nanocomposites. In addition, the effects of nano-silica content, stress level and loading pattern (constant or fatigue loading) on the creep resistance of materials were discussed as well.

This paper presents an experimental study on creep resistance of PI/SiO2 hybrid thin films with silica-fillers weight varying in the range of 0–8%. Creep deformation, creep rate and creep compliance are utilized to evaluate the thin films’ characteristics under constant stress (creep) and tension–tension fatigue tests. The effects of silica doping level, stress amplitude and force pattern (constant or sinusoidal) are also analyzed in the experiments. The results show that the existence of nano-silica can improve the creep resistance both under constant and fatigue loading. Compared with constant loading, fatigue loading can accelerate the creep deformation and creep rate, and significantly increase the creep compliance of PI/SiO2 hybrid thin films in the primary creep stage. As the creep develops into the secondary stage, the stress amplitude will replace the stress pattern and play a dominated role, which is due to the different deformation mechanisms in different creep stages.

The available testing techniques for the coefficient of thermal expansion (CTE) of materials can be divided into two types based on the state of the specimens during test: stress-free and pre-stressed. For traditional bulk specimens, there is no difference since the effect of the pre-stress is very small and can be neglected. However, for thin films, the pre-stress might cause an unacceptable experimental error if its effect is neglected. The related analysis is given in this study. In order to determine the CTE of thin films more accurately, a novel technique for stressed thin films was introduced and some test results for PI/SiO2 nanocomposite thin films were given.

A new technique was proposed to determine the coefficient of thermal expansion (CTE) of thin films at low temperature.Different pre-stress could be applied and the elastic modulus of materials at different temperatures was measured with CTE simultaneously to eliminate the influence of mechanical deformation caused by the pre-stress. By using this technique, the CTEs of polyimide/silica nanocomposite films with different silica doping levels were experimentally studied at temperature from 77K to 287K, and some characteristics related to this new technique were discussed.

Polyimides (PIs) are considered to be one of the most important engineering materials. Much work has been on their organic-inorganic hybrid fabrication process and the related properties at room and elevated temperatures. However, few results were ever involved in their low temperature properties. In this study, PI/SiO2 nanocomposite films were prepared via sol-gel reaction. The coefficient of thermal expansion (CTE) with different silica contents was measured from room temperature to low temperature (77K) and the possible influence of the applied stress level on CTEs was also considered. It is found that CTEs increase at first, then decrease with increasing of silica contents. Another interesting result is that CTEs have a little decrease as the increase of the stress level, though the change is very little in our study. Moreover, the related mechanical properties of PI/SiO2 nanocomposite films (Ultimate tensile strength, Young's modulus and Elongation at break) at room temperature and low temperature (77K) were also reported to give a comparison.

The coefficient of thermal expansion (CTE) is one of the critical design parameters for the application of materials in cryogenic engineering and study of available results demonstrates that thin films have different properties from their bulk counterparts. However, few universal techniques have been developed to measure the CTE of thin films at cryogenic temperatures. Furthermore, the possible effect of the applied stress levels on CTE testing results has not received enough attention. In this study, two novel testing methods, one direct and the other indirect, for determining the CTE of thin films under different applied stress levels at cryogenic temperatures are proposed. The test temperature is from room temperature to 77K and a lower temperature could be reached. Advantages of the two methods are also discussed.