An estimate of maximum ground surface motion for non zero surface velocityEstimation du mouvement sismique maximal à la surface du sol pour une celerite d'ondes non nulle en surface

The increasing need for probability seismic hazard assessment (PSHA) of critical facilities sometimes leads to unrealistic earthquake scenarios with very high induced ground motions. From a physical standpoint these high motions cannot exist because of the limiting resistance capacity of the soil strata through which the seismic waves travel. A simple analytical model is proposed to bound the maximum ground surface acceleration that any soil deposit can transfer. This model is an extension to non zero ground surface velocity of a previously presented model. To cite this article: A. Pecker, C. R. Mecanique 332 (2004).     

An estimate of maximum ground surface motionEstimation du mouvement sismique maximal à la surface du sol

The increasing need for probability seismic hazard assessment (PSHA) of critical facilities sometimes leads to unrealistic earthquake scenarios with very high induced ground motions. From a physical standpoint these high motions cannot exist because of the limiting resistance capacity of the soil strata through which the seismic waves travel. A simple analytical model is proposed to estimate a bound to the maximum ground surface acceleration that any soil deposit can transfer. To cite this article: A. Pecker, C. R. Mecanique 331 (2003).     

Net shape manufacturing and the performance of polymer composites under dynamic loads

An experimental investigation was conducted to determine the influence of postmold trimming and resultant edge quality on the performance of fiber-reinforced plastics (FRP) under dynamic loads. Graphite/epoxy and graphite/bismaleimide laminates were machined using three state-of-the-art industrial techniques and subjected to three-point bend impact to failure. The load load-line displacement records were used to obtain the load, bend deflection and energy absorbed to fracture. High-speed photography was also employed to identify the initiation and progression of failure and record the time dependent fracture process. From a comparison of edge quality and subsequent material performance for both polymeric composites, it was found that the impact response of FRPs is highly process dependent. In general, the load and energy absorbed to fracture decreases with increasing surface roughness. Reductions in the load and energy to the onset of fracture with degrading surface quality were as high as 20 percent. The dynamic response was also found to be dependent on the constituents, stacking sequence and impact velocity.     

Fluctuation strength of modulated sound radiated from rectangular plates with mixed boundary conditions

A generalized differential quadrature method is developed for solving the sound radiated from the forced vibrating rectangular plates with mixed boundary conditions in this paper. The fluctuation strength of the radiated sound, which is modulated by another sound near the plates, is studied. The effects of the modulation frequency and the modulation degree on fluctuation strength are revealed. The effects of the radiated sound frequency and the structural modal density are also studied and compared. The numerical results are presented to show the characteristics of the fluctuation strength of the modulated sound radiated from rectangular plates with mixed boundary conditions.     

Dynamics of a nearly symmetrical piecewise linear oscillator close to grazing incidence: Modelling and experimental verification

Experimental studies and mathematical modelling have been carried out for a nearly symmetrical piecewise linear oscillator to examine the bifurcation scenarios close to grazing. Higher period responses are found after grazing, although the period adding windows predicted as a generic feature of one-sided impacting systems are not observed. It appears that the presence of the second high stiffness spring stabilises additional periodic orbits. The global solution for a piecewise smooth model is developed by stitching locally valid maps. For the symmetrical case the highest period of response is three, if asymmetry in the gap and/or stiffness is introduced then higher periodic orbits are observed. Only small asymmetries are required to achieve a good correspondence with experiments. Further examination shows that many attractors are not stable to even small changes in the symmetry of the system.     

UNIFIED STRENGTH THEORY AND ITS APPLICATION

This book provides a new Unified Strength Theory and describes its applications. The Unified Strength Theory is a system of yield and failure criteria of materials under complex stresses. It covers the entire range of convex failure criteria, from lower bound (Tresca yield criteria and Mohr-Coulomb failure criteria) to upper bound (twin-shear failure criteria). It also includes the non-convex yield and non-convex failure criteria. A series of new failure criteria and previous failure and yield criteria can be deduced from the Unified Strength Theory. The work presented in this book is unprecedented in the field of strength theory. It is useful for students in understanding the strength theory, for engineers to correctly use it and for researchers to choose an appropriate failure criteria in studying the strength of materials and structures. An experimental verification, engineering applications, a detailed historical review and more than 1000 references are provided. Written for Researchers in applied mechanics and materials science     

超高真空下过渡金属Nb与Nb、Ta、Ti、W相互间粘附特性的试验研究

本文在超高真空(10~(-7)Pa)条件下量测了Nb-Nb(110)、Nb-Ta(110)、Nb-W(110)及Nb-Ti4个粘附对的粘附力,并从接触表面形貌的角度求得了真实接触面积,进而得到了各粘附对间的粘附强度,结果与采用简单紧束缚自洽矩方法计算所得理论结果一致。研究表明,超高真空下过渡金属间存在一种相互作用——由两金属间共用电子引起的化学键,而且主要由其外层d电子态密度所决定。过渡金属Nb与Nb、Ta、W、Ti之间粘附强度的实测值介于每对原子0.2～2.0eV之间。当样品受热升温后,由于C、N、B、S等少量非金属杂质的表面偏析致使粘附强度明显降低。     

Quasi-harmonic analysis of the behaviour of a hardening Duffing oscillator subjected to filtered white noise

The behaviour of a hardening Duffing oscillator subjected to narrow band random excitation is examined. The influence of possible jumps, between competing states, on the probability distribution of the response amplitude is addressed. A quasi-harmonic approximation of system behaviour is adopted which is capable of reproducing the observed concave shape of probability functions and compares well with predictions obtained via stochastic averaging techniques and with digital simulations.     

Enhancement on interlaminar shear strength and water‐lubricated tribological performance of high‐strength glass fabric/phenolic laminate by the incorporation of carbon nanotubes

High‐strength glass fabric (HSGF)/phenolic laminates modified with different contents of carbon nanotubes (CNTs) were fabricated by hot‐compression technique. The effects of CNTs on the interface of HSGF/phenolic, interlaminar shear strength (ILSS) and water‐lubricated tribological performance of HSGF/phenolic laminate were investigated. The ILSS of the laminates were tested on a universal testing machine (DY35), and the tribological properties were evaluated by a block‐on‐ring tribo‐tester. The interfaces of HSGF/phenolic and the worn surfaces of the laminates were analyzed by scanning electron microscope. The results showed that the moderate incorporation of CNTs improved the interface of HSGF/phenolic and accordingly enhanced the ILSS of the laminate. Besides, the friction coefficient of HSGF/phenolic laminate sliding against stainless steel in water can be remarkably stabilized and lowered by the incorporation of CNTs due to the better water lubrication induced by added CNTs and the intrinsic self‐lubrication of CNTs which were further graphitized during the friction and wear process. And the wear rate of the laminate can be accordingly reduced by 1 order of magnitude. The results indicate that CNTs have excellent potential in enhancing both ILSS and tribological fabric/polymer laminate composite, which will greatly improve the current situation of deterioration on mechanical properties by adding traditional solid lubricants. Copyright © 2014 John Wiley & Sons, Ltd.     

Compressive char strength of thermoplastic polyurethane elastomer nanocomposites

This research encompasses the study of testing protocols and the design of sensors for evaluating the compressive strength of the char layer of ablative material used in solid rocket motors (SRMs). The testing protocol that has been developed is the continuation of previous work for determining the compressive strengths between different SRM insulation materials. A crushing test method was further developed, and a sensor platform was assembled to perform the tests. The test procedure consists of measuring the amount of force required to crush a given area of the charred sample for a specified depth. The test was repeated for the industry standard Kevlar®‐filled ethylene propylene diene monomer rubber and thermoplastic polyurethane elastomer nanocomposite with different weight loading of multi‐walled carbon nanotubes, montmorillonite nanoclay, and carbon nanofibers. The energy of destruction or energy dissipated was quantified to determine which ablative exhibited the best performance. Maximum force was also recorded as a secondary quantity to determine char strength. The proposed test method is fully automated to ensure repeatability of each measurement and to remove the potential for human‐induced error. Because char layer thickness varies depending on the material, a method of differentiating neat material from char was proposed and explored. The introduced procedure also represents a novel and unique approach to solve the problem of the determination of the char strength. Copyright © 2014 John Wiley & Sons, Ltd.