The past, present, and future of fracture mechanics

The science of fracture mechanics was born and came to maturity in the 20th century. Its literature is now vast. Perhaps the most successful application of fracture mechanics is to fatigue. However, this short paper is limited to a core topic of fracture, the initiation and propagation of fracture under monotonic loading at low strain rates.As the author was invited to present this paper on the occasion of his 65th birthday, it is a somewhat personal view of the development and future of fracture mechanics, but it is hoped that it will interest many, especially the young researchers at the beginning of their careers.     

通信声学:过去、现在和未来

通信声学的定义:通信声学是面向人与人、人与机器之间的信息交互,研究一般声学环境中音频信号的产生、传播和接收的声学分支学科。基于现代声学、信息处理和通信技术的发展,通信声学已成为一个多学科交叉的研究领域。它融合了心理生理声学、房间声学、电声学、语音和音频信号处理、通信技术、计算机技术等不同领域的研究成果,在当今的科学与技术变革中具有显著的位置。     

Wire-woven cellular metals: The present and future

Wire-woven metals are a type of cellular metal composed of uniform 3D truss-like cells, and fabricated using wires as the raw material. Wire-woven metals are practically the most common choice for lattice truss metals to achieve multi-layered structures with fine cells. Since the new millennium, a number of wire-woven metals have been developed. This paper reviews various wire-woven metals and introduces their topologies and fabrication processes. In addition, their mechanical and thermal properties with analytic solutions, their variations, and applications are presented. Finally, the limits and prospects of wire-woven metals are discussed. The future of wire-woven metals seems promising due to the many options in the selection of the mother material, cell size, overall size, relative density, and cell geometry. Furthermore, their mechanical and thermo-hydraulic properties are superior to their competitors such as metal foams and they can be mass-produced at low cost.     

Modelling slit tape buckling during automated prepreg manufacturing: A local approach

This paper investigates the local buckling of slit tape in the Automated Fibre Placement process for a circular fibre path using an analytical approach that accounts for prepreg tack and stress distribution. Curing effects are not considered in this study. The main objective is to define the critical buckling load and therefore the minimal steering radius for which no tow wrinkling occurs. Simulations are performed for the buckling of the first ply, using a tack parameter governing the interaction between tool and material. A sensitivity analysis of the most relevant parameters of the model is performed. Numerical results show that lower values of the steering radius are obtained for lower tow width values and higher prepreg tack values. Experimental investigations show that the estimation of wrinkling occurrence in steered fibres could be improved by taking into account certain additional parameters, such as lay-down rate, temperature and the dynamic behaviour of the resin.     

Service multinationals: Their past,present, and future

Abstract and Key Results

EMACK improvements, present and future

A three-step program has been developed to improve the single-shot performance and to add 1-Hz repetitive operation capabilities to the EMACK electromagnetic launcher system. Single-shot performance is improved in two steps: first by copper-plating the HPG (homopolar generator) rotor, increasing the switch shuttle surface area, and developing a stronger barrel; and then by augmenting the inductive store support structure to withstand the increased electromagnetic forces at higher current, modifying the HPG rotor with a Be-Cu sleeve, and adding a flywheel. These modifications will allow operation of the system at a peak current of 2.2 MA. Repetitive operation of the system is gained by significantly modifying the linear rail switch to accommodate multiple shuttles, adding a repetitive loader, and cooling the muzzle and dump resistors. Larger masses could be accelerated by increasing the size of the flywheel. Repetitive operation of the EMACK launcher at frequencies in the neighborhood of 1 Hz is made possible by using a high-resistance muzzle resistor to drop the HPG current to a low value between shots