Effect of Repeated Wetting-Drying-Freezing-Thawing Cycles on the Mechanic Properties and Pore Characteristics of Compacted Loess

A series of laboratory experiments, including oedometer tests, direct shear tests, and mercury intrusion porosity (MIP) tests, were conducted to investigate the effects of repeated wetting-drying-freezing-thawing (WDFT) cycles on the mechanic behaviors and pore characteristics of compacted loess. The results of mechanical tests indicate that the WDFT weathering can cause significant deterioration of mechanical properties for compacted loess. As the number of treatment cycles increases, vertical compression strain and coefficient of collapsibility of the loess specimens increase while the cohesion decreases. The compacted and noncollapsible loess specimen exhibits collapse again after the 7 WDFT cycles. The results of MIP tests show that WDFT cycles have a main influence on the pores with a pore diameter of 1∼35 μm between the soil aggregates, and medium pore contents (10∼35 μm) increase significantly with the increasing number of WDFT cycles. By comparing compression and collapse characteristics of the loess specimens subjected to wetting-drying, freeze-thaw, and WDFT cycles, we found that the dry-wet action plays the dominant role in the deterioration of engineering properties of compacted loess during WDFT cycles.

Bending collapse of treble rectangular thin-walled tubes and its application in conceptual design for automobile crashworthiness

The aluminium profiles of treble rectangular thin-walled tubes (TRTWT) manufactured by extrusion processes are extensively applied in energy absorption structures of automobile due to the high crashworthiness and stiffness-to-mass ratio. Therefore, this paper investigates the bending collapse characteristics of the TRTWT and its application in conceptual design for automobile crashworthiness. Firstly, the bending collapse behaviours of the TRTWT are obtained through experimental method. Then, the analytical expressions for the bending collapse characteristics are derived in detail by using the global energy equilibrium theory, which are validated by comparing with experimental and numerical results. Furthermore, the bending collapse characteristics are applied in the simplified model to conduct crashworthiness analysis and optimization for the conceptual design of the automobile with the TRTWT, which can enhance the crashworthiness and greatly shorten design cycle. Finally, application examples for the front-end and side-wall structures of automobile demonstrate that the simplified model with the analytical bending collapse characteristics can be used as a substitute of detailed model for accelerating crashworthiness design of the automobile with the TRTWT.

Dynamic crushing force of rotational ellipsoidal composite shells-filled foam

This paper presents an analytical method to solve the dynamic crushing force and collapse characteristics of rotational ellipsoidal composite-reinforced metal shells with foam filler. The collapse model is firstly simulated by means of finite element calculation. Then, the feasibility of the analytical method is proved by a comparison with the finite element simulate. In example calculations, effects of some key parameters on the dynamic crushing force of rotational ellipsoidal composite-reinforced metal shells with foam filler are described and discussed. Results obtained can be used as a valuable reference for the design of protective structures resisting impact loads.

Experimental study on the effect of a deformable boundary on the collapse characteristics of a cavitation bubble

Cavitation phenomena widely exist in many fields such as medical treatment, chemical engineering, and hydraulic engineering. The boundary properties have a great influence on the collapse characteristics of a cavitation bubble. The interaction between a cavitation bubble and a boundary of different properties is an important part in the cavitation erosion mechanism. In this paper, cavitation bubbles under in-water pulse discharge and cavitation erosion under ultrasonic vibration were used to study the effect of a deformable boundary on the collapse characteristics of a cavitation bubble, which reveals the cavitation-resistance performance of different materials on the macroscopic scale. The main experimental results showed that on a deformable boundary, the cavitation bubble does not collapse toward the boundary in the later collapse stage compared with on the rigid boundary. The collapse process of the cavitation bubble is aggravated on the deformable boundary. In the condition of same cavitation strength, the cavitation?s erosion loss amount on the rigid boundary material is much higher than that on the deformable boundary material. The experimental conclusions have an important reference value for the development of cavitation erosion prevention and the exploration of cavitation-resistance materials.