Key Engineering Materials Vols. 417-418

Abstract: In this paper, the influence of deep cryogenic treatment (DCT) on mechanical properties of two commercial steels is analysed. Hardened AISI 302 stainless steel and 18NiCrMo5 carburized steel specimens were subjected to DCT after standard treatments. For both materials, the fatigue behaviour is a key property considering their usual applications requirements. Surface hardness, tensile properties and axial fatigue resistance of both materials were measured and compared with and without DCT. From the analysis of the experimental results and from their interpretation in the light of the previous literature, some useful indications are obtained about the DCT potential fallout on design and construction of structural components.

Abstract: The aim of this work is to investigate the (rolling) contact fatigue behaviour of transmission spur gears coated with PVD (Physical Vapour deposition) thin hard films. Numerical models of coated steel and titanium spur gears were developed. The effect of the residual stress gradient induced by the coating deposition process was considered in the calculations. A theoretical-numerical procedure was arranged to foresee the crack propagation direction. Such a procedure could represent a powerful tool to predict the (rolling) contact fatigue resistance of PVD-coated gears.

Abstract: In this paper a review of the state of the art on the study of the fatigue and the contact/rolling contact fatigue (RCF) resistance of thin hard-coated components is provided. Physical and chemical vapor deposition (PVD and CVD) methods are used to deposit such films. A fair number of references reports experimental data highlighting the improvements achieved with coating deposition on both steels and light alloys. Numerical modelling has also been devoted to shedding light on the behaviour of coated components and reliable previsional procedures have been arranged to foresee the number of cycles until fatigue damage initiation and failure.

Abstract: Subjecting to the compressive membrane action (CMA), the ultimate load capacity of the reinforced concrete (RC) slab with lateral restraint would be improved obviously. Test of 12 one-way slab specimens restrained by shear-walls was carried out to investigate the properties of the slab strips’ compressive membrane action. The reduced-size specimens were designed to keep the ratios of shear-walls’ restraint stiffness to slab strips’ flexural stiffness unchanged. One horizontal testing instrument was first used to record the development of the slabs’ lateral restraint forces. The ultimate loads of slab strips with certain lateral restraint stiffness gave an average 38.3% rise from the calculations of upper-bound method. Though the increment of slab’s ultimate load was due to the additional moment formed by the lateral restraint force, the results showed that the peak of lateral force lagged of the slab strips’ ultimate load, which was different from the previous hypothesis. Various parameters which affect the development of CMA were also investigated, such as the shear-wall’s thickness, axial load on the walls, the slab strips’ span-height ratio and reinforcement percentage.

Abstract: Investigation on crack propagation is important to understand mechanical behaviors and fracture mechanism in concrete. Till now substantial work has been done on crack propagation under mode-I loading, and mixed-mode fracture mechanics problems, however, are more common for actual crack growth. This study aims to systematically investigate the crack initiation, stable propagation and unstable failure of concrete under I-II mixed mode condition by using photoelasticity technique. For this purpose, reflective photoelastic coatings were applied to the surface of the four-point shearing notched concrete specimens with the maximum size of 2500mm×600mm×200mm. The resulting interference fringe on photoelastic coatings was recorded to reflect a complete crack propagation process. Based on the colored strain sequence, the strain profile around the crack tip could be determined and thereafter the load-crack extension curve. Then finite element analysis was performed to simulate the process of crack propagation and corresponding stress intensity factors were solved for every step. Experimental results show obvious stable crack propagation in concrete before unstable failure under I-II loading condition. The conventional failure criterion with the absence of this stable propagation quantity is therefore conservative. Besides, the fracture mode is ultimately I-mode even the specimen is subjected to I-II mixed mode loading condition, that is, the crack will extend in a direction perpendicular to the peak principal stress.

Abstract: The damage of structure leads to variation of structural modal parameter，so the wavelet transform for damage detection is introduced in this paper for considering the variation. First, structural dynamic response signal on the basis of the vibration-based structural damage diagnosis methods is calculated by structural analysis in the paper, then, each of sub-signals is calculated according to wavelet analysis, also, the sub-signal energy spectrum of dynamic response signal and energy spectrum variation are known. By observing the difference of the sub-signal and the variation of the sub-signal energy spectrum, we can get the variation of structural modal parameter and the sub-signal energy spectrum due to the performance degradation of the whole structure and local variations of damage level and location ,so that this method can be used in on-line damage detection for bridge structure.

Abstract: The national standard《Post-earthquake field works Part 4: Assessment of direct loss》 (GB 18208.4-2005) has been playing an important role in earthquake loss assessment, relief organization and homeland rehabilitation since it was issued in 2005 in China. The earthquake losses assessed are much less than other natural disasters (such as floods, drought) or foreign earthquake losses. How to assess seismic economic loss reasonably has been a key issue domestic seismic workers concern. In this paper, an earthquake-induced building decoration loss assessment method for urban zones is presented firstly. Then, based on statistical analysis of collected more than 600 pieces of cost data and 30 pieces of expert questionnaires, the distribution proportion of moderate–and–high–grade decoration building, the proportion of decoration cost and total structure cost, the loss ratio of decoration damage in small, Medium and big cities are given, respectively. The correction coefficients are also given depending on different economic development and use. Finally, its practical application in Sichuan Wenchuan Ms8.0 great earthquake loss assessment is introduced. Thus, some references and basis for further modifying and perfecting earthquake loss assessment standard in China are provided.

Abstract: A great earthquake of magnitude 8.0 occurred on May 12, 2008 (Beijing Time) in Wenchuan, Sichuan Province of China, caused huge casualties and economic losses. As a member of field investigation team of China Earthquake Administration (CEA), the decoration and indoor/outdoor properties losses of the earthquake-stricken areas were investigated in detail, which include Dujiangyan, Mianyang, Deyang, Chengdu, Guangyuan city, and other areas. In this paper, based on statistical analysis of collected survey data, the investigation results and characteristics of buildings decoration and indoor/outdoor properties losses of the earthquake-stricken areas are given firstly. Then, the relationship between decoration damage grade and main body structure damage grade is analyzed, and loss ratio of building decoration damage in urban zones is also provided on the basis of expert questionnaires. Thus, some foundations are established for loss assessment method of building decoration damage in urban zones.

Abstract: Strength mismatch effect across weld interfaces, generated by welding weak and strong steels, influences fatigue and fracture properties of a welded bimetallic composite. Advancing fatigue crack tip in weak parent steel is shielded from the remote load when it reaches near the interface of ultra strong weld steel. Entry of crack tip plasticity into weld steel induces load transfer towards weld which dips crack growth rates thereby enhancing the fatigue life of the composite. A computational model for fatigue life prediction of strength mismatched welded composite under K dominant conditions is validated by experimental work in this paper. Notched bimetallic compact tension specimens, prepared by electron beam welding of weak alloy and strong maraging steels, are subjected to fatigue testing in high cycle regime.

Abstract: Since lightweight aggregate usually accounts for a higher percentage of the concrete by volume, the properties of lightweight aggregate can significantly influence the properties of the resulting concrete. In this study, we investigated the effects of the water content of lightweight coarse aggregate (LCA) on freeze-thaw resistance of lightweight aggregate concrete (LC) and analyzed how to control the fatal frost damage - cracks in LC. The results showed that the freeze-thaw resistance of LC was determined by the water content of LCA. It is clear that lowering the water content of LCA below 17% is the key method to secure the freeze-thaw resistance of LC. The study showed that the higher the water content of LCA, the higher the weight loss and the larger pore volume of LCA, the bigger the length expansion and the lower the durability factors of LC after freezing and thawing. Internal cracks occurred only in the concrete specimens that contained LCAs with higher water content when subjected to freezing and thawing. Expansion pressure occurred easily in the higher water content LCAs and micro-cracks formed initially in the weak grains. Then micro-cracks enlarged and spread to the mortar as the number of freeze-thaw cycles increased. This process eventually caused LC expansion and damage.