Estimation of the Fatigue Endurance Limit of HMAC for Perpetual Pavements

A simplified procedure was described to estimate the FEL of three kinds of hot-mix asphalt concrete （HMAC） without doing any fatigue tests. The procedure required two fundamental properties of HMAC, tensile strength under different temperatures and strain rates, and flexural stiffness under different stain levels. This information can reliably be obtained in simple tests, which are the monotonic uniaxial tensile test （MUTT） and the four-point bending test （FPBT）. A new parameter, the initial stress ratio Rinitial, was introduced to connect these two tests, which was defined as the ratio of applied initial stress and tensile strength of the specimen. At last the FEL can be expressed as a function of the initial flexural stiffness, frequency and temperature. Obviously, this procedure has the potential to be very useful in view of long-life pavement design and time consuming traditional fatigue tests.

Heat treatment enhancing the compressive fatigue properties of open-cellular Ti-6Al-4V alloy prototypes fabricated by electron beam melting

In this work, we report the effect of annealing in α＋β phase field on the fatigue properties of Ti-6A1-4V alloy meshes fabricated by electron beam melting. The results show that annealing at high temperature near the phase boundary enhances the ductility of the brittle mesh struts due to the formation of coarse α lamellas with a large thickness/length ratio. Accordingly, the fatigue endurance ratio of the studied meshes increases to up to -0.6, which is much superior to that of the as-fabricated counterparts and comparable to those of dense materials.2018 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology.

Achieving excellent energy storage reliability and endurance via mechanical performance optimization strategy in engineered ceramics with core-shell grain structure

Although dielectric ceramic capacitors possess attractive properties for high-power energy storage,their pronounced electrostriction effect and high brittleness are conducive to easy initiation and propagation of cracks that significantly deteriorate electrical reliability and lifetime of capacitors in practical applications.Herein,a new strategy for designing relaxor ferroelectric ceramics with K_(0.5)Na_(0.5)NbO_(3)-core/SiO_(2)-shell structured grains was proposed to simultaneously reduce the electric-field-induced strain and enhance the mechanical strength of the ceramics.The simulation and experiment declared that the bending strength and compression strength of the core-shell structured ceramic were shown to increase by more than 50% over those of the uncoated sample.Meanwhile,the electric-field-induced strain was reduced by almost half after adding the SiO_(2) coating.The suppressed electrical deformation and enhanced mechanical strength could alleviate the probability of generation of cracks and prevent their propagation,thus remarkably improving breakdown strength and fatigue endurance of the ceramics.As a result,an ultra-high breakdown strength of 425 kV cm^(-1) and excellent recoverable energy storage density(Wrec~4.64 J cm^(-3))were achieved in the core-shell structured sample.More importantly,the unique structure could enhance the cycling stability of the ceramic(Wrec variation<±2% after 105 cycles).Thus,mechanical performance optimization via grain structure engineering offers a new paradigm for improving electrical breakdown strength and fatigue endurance of dielectric ceramic capacitors.

Features of the electrophysical and mechanical properties of n-component ferroactive solid solutions of composition PZT-PZN-PMN

Study of the fatigue endurance and mechanical strength of solid solutions of the PZT-PZN-PMN system,modified with Ba and Sr,corresponding to the formula(Pb_(1-a_(1)-a_(2))Sr_(a_(1))Ba_(a_(1)))[Ti_(x)Zr_(y)<(Nb_(2/3)Zn_(1/3))(Nb_(2/3)Mg_(1/3))>_(1-x-y)]O_(3),with a_(1)=0.02÷0.12;Da_(1)=0.02,a_(2)=0.0036÷0.073;x=0.385÷0.430,y=0.402÷0.447 is presented.It is shown that the evolution of the polarization characteristics with an increase in the number of repolarization cycles,n,is characterized by two sections:slow fatigue and logarithmic evolution.It was found that an increase in the strontium content shifts the beginning of the logarithmic stage towards to the large n.It is shown that an increase in the average grain size decreases the mechanical strength.A conclusion is made about the expediency of using the obtained data in the development of devices operating in power modes.