Quantifying damage evolution within olivine basalt based on crack propagation behavior under microwave irradiation

Application of microwave heating technique is highly promising in assisting rocks breakage and recycling coarse aggregate in waste concrete. This work focus on crack propagation behavior and hence damage of hard rocks subjected to microwave irradiation. Heating effects of basalt and its main mineral components are investigated experimentally using a multimode industrial microwave system. Crack characterization of basalt after irradiating are observed using scanning electron micrograph (SEM). A theoretical model based on heating effects of mineral components is established to deduce crack propagation within basalt under microwave irradiation. Temperature rise of magnetite is drastic while that of other mineral components are tardy. Fracture of basalt is induced by predominant radial crack propagation around the rapidly heated mineral particle. Cracks can be divided into short cracks and long cracks by a characteristic length during extending. Microwave energy required for extension of cracks with characteristic length is minimum. Propagation of initial short cracks results in greater extent of damage evolution instantaneously. Moreover, damage increases with the mineral content of magnetite and decreases with crack density.

Dislocation-toughened ceramics

Dislocations are mobile at low temperatures in surprisingly many ceramics but sintering minimizes their densities. Enabling local plasticity by engineering a high dislocation density is a way to combat short cracks and toughen ceramics.

Influence of inspection on the safety of fatigue loaded welded cruciform steel joints – comparison of simplified and advanced crack growth models

<p>Probabilistic fatigue life prediction models of welded steel joints are often used to estimate the level of safety, which is given in terms of the probability of failure or the reliability index as a function of the applied load cycles. Prediction models based on fracture mechanics allow taking into account the effect of inspections on the estimated level of safety. Recent developments in fracture mechanics based fatigue prediction models allow modeling the behavior of short and long fatigue cracks under constant and variable amplitude loading. Short cracks are relevant since their growth characterizes most of the fatigue life, especially under service loading. A recently proposed model by the authors is considered and compared to a more traditional and simplified model as proposed in the standard BS7910, where no distinction is made between short and long cracks. The effect of the model uncertainty, the type of inspection, and the time of the inspection on the estimated level of safety are quantified for welded cruciform steel joints.</p>

A new Track of Fatigue crack growth in Aluminum Alloy (2219) under Cyclic Stresses

A study of new Track of Fatigue crack growth in aluminum alloy (2219) under cyclic stresses has been made. It was found out that this crack grow and propagate in three phases, the first phase though the grain size (micro-structure short cracks(MSC)), second phase cross the boundary of the grain size to about 1mm in length (physically short cracks (PSC)) and the third phase up to the final fracture (Length cracks(LC)). In addition, two programs were designed on MATLAB to perform the compute calculations to collect the results. The first program to calculate the practical constants and the second to make the calculations required to complete the work schedules. The stress and the parameters effecting the growth of these cracks in each phase were studied. A model consisting of three formulas was established from the experimental results. Each formula describes the behavior of the cracks in the particular phase. The comparison showed that the proposed model is safer than the experimental results for the designed parts of aircraft.

Effect of Diamond Surface Pretreatment and Content on the Microstructure and Mechanical and Oxidation Behaviour of NiAl/Fe-Based Alloys

The effect of diamond surface pretreatment and content on the microstructure and mechanical properties of NiAl/Fe–x diamond (x=0,5,10,15,and 20 wt.%) alloys was investigated after mechanical alloying with subsequent hot-pressing sintering. The results showed that after the surface pretreatment, a complete transition layer containing W existed on the outer surface of the diamond grains, which improved the interfacial bonding strength of the diamond grains and NiAl/Fe matrix to an excellent level. As the diamond content increased, the compressive strength of the NiAl/Fe-based alloys declined, but the alloy with 10 wt.% diamond had a higher value than that of the other NiAl/Fe-based alloys. Short cracks and transgranular fracture were observed in the fracture surface of all materials. For the material with 20 wt.% diamond, intergranular fracture was obvious, and many diamond particles appeared along the fracture direction, which caused the compressive strength to be the lowest of the samples considered in this study. After the addition of diamond, the oxidation resistance of NiAl/Fe-based alloys decreased due to a loose oxidation layer and diamond graphitization. The thermal conductivity of the alloy first increased and then decreased with increasing diamond content. A NiAl/Fe-based alloy with 15 wt.% diamond demonstrated the maximum thermal conductivity of 53.2 W/(m·k) at 600°C among the samples in this study.

Results From Environmentally-Assisted Short Crack Fatigue Testing on Austenitic Stainless Steels

The effect of environment on fatigue life is currently assessed using methods (such as NUREG/CR-6909) that may be excessively conservative when applied to plant components and loading transients. To reduce this conservatism, the ASME WG-EFEM has proposed the development of an improved assessment methodology for environmental fatigue based on a Total Life Prediction approach that would be adequately, but not excessively, conservative. Such an approach necessitates the development of analytical methods for the various stages of crack nucleation, short crack growth and long crack growth. Hence, there is a requirement to undertake testing within the short crack growth regime that would bridge the gap between fatigue nucleation and long crack growth (Paris Law) enabling better prediction of total life measured by fatigue endurance. A test methodology has been developed by Wood to enable short crack growth testing with in-situ monitoring using DCPD. Testing has been undertaken in both high temperature air (300°C) and simulated end-of-cycle primary water chemistry at 300°C on cold-worked stainless steel specimens, which were subject to a range of load ratios and rise times. FEA modelling has been undertaken to determine the effective stress intensity factors applied under the loading conditions based on the specific material properties. This paper presents the results from a testing program conducted with EPRI, to measure fatigue crack growth data for short cracks from 0.15 mm to 1.0 mm. Crack growth rates have been compared to those predicted in ASME, Code Case N-809 and results from material specific in-house testing to assist the understanding of the behaviour of mechanically short cracks.