A B S T R A C T An experimental method was developed to quantify the multi-site fatigue crack initiation behaviour of engineering alloys in four-point bend fatigue testing under stress control. In this method, fatigue crack initiation sites [fatigue weak-links (FWLs)] were measured on the sample surface at different cyclic stress levels. The FWL density in an alloy could be best described using a three-parameter Weibull function of stress, although other types of sigmoidal functions might also be used to quantify the relation between weak-link density and stress. The strength distribution of the FWLs was derived from the Weibull function determined by fitting the weak-link versus stress curve experimentally obtained. As material properties, FWL density and strength distribution could be used to characterize the fatigue crack nucleation behaviour of engineering alloys quantitatively and evaluate the alloy quality in terms of weak-link density and strength distribution. In this work, the effects of environment, types of microstructural heterogeneities and loading direction on FWLs were all studied in detail in AA7075 T651, AA2026 T3511, A713 alloys, etc. It was also found that FWL should be quantified as a Weibull-type function of strain instead of stress, when the applied maximum cyclic stress exceeded the yield strength of the tested alloy.Keywords A713 cast Al alloy; four-point bend fatigue test; fatigue weak-link (FWL) density; high strength Al alloy; multi-site fatigue crack nucleation; strength distribution. N O M E N C L A T U R EC = a scaling constant FIB = focused ion beam FEA = finite element analysis FWL = fatigue weak-link HCF = high-cycle fatigue k = constant L = rolling m = Weibull modulus n = the characteristic strength distribution of FWLs N = the number of fatigue weak-links at a specific stress level N 0 = the fatigue weak-link density OM = optical microscopy RH = relative humidity S = short transverse SEM = scanning electron microscopy T = long transverse ε = the strain associated with the applied stress σ ε 0 = the strain measured at stress of the fatigue limit σ 0 σ = stress level σ s = the ultimate tensile strength σ 0 = fatigue limit Correspondence: T. Zhai.

Effects of amount of Ca on crystal structure, microstructure, ferroelectric properties, and dielectric properties of the CaxSr2-xBi4Ti5O18 (CSBTi-x) ferroelectric ceramics were investigated. The results show that single-phase layered perovskite ferroelectrics were obtained and no appreciable secondary phase was found.Ca-doping results in a notable enlargement of remnant polarization 2Pr. The 2Pr of CSBT-0.15 reaches a large value, the remnant polarization 2Pr and coercive field 2Ec were 18.1µC/cm2 and 120.2kV/cm, respectively. Dielectric constant and dielectric loss of CSBT-0.15 was also measured, showing dielectric constant εr=199~194 and dielectric loss tanδ=0.02~0.014 over the range of 100 kHz~1MHz, respectively.

The sintering of alumina ceramics with high-purity has gained much attention due to their wide range applications. The improved sinteirng methods, such as the spark plasma sintering, super-high pressure sintering, two-step sintering, and so on, have advantages on the decreasing the sinteirng temperature or inhibiting the grain coarsening, compared with the conventional sintering.

Abstract. Calcium carbonate concrete is a normally concrete in the area with rich limestone. With the heavy use, a large of Calcium carbonate concrete waste is generated, how to reuse the waste is an important problem. The generation of reactive powder concrete (RPC) with silica fume is relative more expensive than normal concrete. Using the calcium carbonate concrete waste instead of silica fume in RPC can realize the recycling of construction and demolition waste, moreover, the high price of RPC manufacture can be decreased. The study mainly focused on the mechanical properties and durability as well as the microstructure of RPC with calcium carbonate concrete waste powder (CCWP) instead of silica fume, the results confirmed that the mechanical strengths of 3, 7, 28 days of RPC with CCWP did not obviously decrease, freezing and thawing test could attain to 500 recycles without obvious destruction and carbonation did not happen after 28 days. RPC with CCWP had no more amorphous material and good crystallinity, its microstructure was dense as that of RPC without CCWP.

A brick material was prepared with marble wastes as main raw material by pressure forming and water-curing at room temperature. With the increases of the amounts of water additions, the compressive strength increased gradually and obtained a highest value of 34.8MPa in the sample of the ratio of cement: wastes=20:100 at 17.0% water addition, above which the strength had an adverse change and decreased. The addition of glass fiber had small effects on the strength, water absorbing rate and density comparing with that of wood flour. The strengths of sample had changed obviously with the increment of the forming pressures. However, the strength would fall because of the lamination caused by the recovering effects of the wood flour in the sample with replacement of the wood flour to marble wastes, as the forming pressures were higher than 5.0 MPa.