查看更多>>摘要：The evolution of concrete behavior in the proximity of a joint under the effect of varying external pressures is studied by means of a novel nonlinear ultrasonic technique denoted as Scaling Subtraction Method. The results obtained show that the proposed method is effective in describing the occurrence of micro-structural changes near the joint and detect potential conditions for crack opening and damage initiation.
查看更多>>摘要：In this paper a higher order crack path simulation algorithm for multiple interacting cracks is presented using piecewise parabolic curved increments including the consideration of the plastic limit loads. For this reason, the program PCCS-2D has been extended to analyse the crack growth and the plastic limit load for each crack propagation step in a fully automatic simulation. The proposed solution algorithm provides a powerful tool for flaw assessment with the FAD procedure in combination with a numerical crack path simulation. Several numerical examples are presented to show the accuracy and the efficiency of the crack path simulation including the analysis of the plastic limit loads.
Paolo BaldisseraStefano CavalleriPaolo MarcassoliFederico Tordini...
49-52页
查看更多>>摘要：In this paper the influence of DCT (Deep Cryogenic Treatment) and a CrN arc-deposited PVD (Physical Vapor Deposition) coating on the fatigue behaviour of AISI 302 stainless steel was studied. Rotating bending tests were carried out on standard specimens to evaluate the fatigue limit at 300000 load cycles. The single and the combined effects of the two treatments were investigated by addressing untreated, PVD-coated and both PVD-coated and DC-treated specimens to the tests. All the series of specimens were also tested statically and laboratory analyses including fracture surface SEM observations and hardness measurements were performed.
查看更多>>摘要：A new class of metal/ceramic composites has recently been developed. A porous ceramic preform, the pore structure of which is created via a freeze-casting technique, is melt-infiltrated with metallic alloy via sqzeeze-casting. The microstructure of the composite has lamellar-like domains with geometrical characteristics which are dependent on the manufacturing parameters. The aim of our study is to find a good micromechanical model in order to deduce the mechanical propertics of the single domains and of the whole material as a function of the microstructural geometry and the material parameters of the ceramics (alumina) and the alloy (Al-Si eutectic). Firstly, the statistical analysis of polarized light microscopic micrographs of the cross section of the specimen was performed. Domains with the same orientation of lamellae, so-called single domains were detected. selected and measured. The material modeling was performed by a two-step homogenisation procedure using a combination of different micromechanical models. Predicted material properties were compared with ultrasonic measurements for a single domain and for the whole microstructure.
I. Fernandez ParienteS. BagheriR. GhelichiM. Guagliano...
57-60页
查看更多>>摘要：Effects of surface defect size and the method used to obtain the defect itself on bending fatigue behaviour of nitrided and shot peened steel was studied. Two different series of 15 sandglass specimens with a microhole in the minimum section generated after nitriding and shot peening treatments were considered. In one series the microholes were obtained by controlled electro-erosion. In the other series microholes were obtained by indentation, much more invasive that electro-erosion, simulating a damage due to a mechanical impact or scratch on the surface material, common on real components during the life span. In both cases the microholes act as a pre-existent crack. The results show that defects obtained by indentation lead to a minor fatigue limit with respect of larger defects obtained by electro-erosion. This was interpreted as the modification of the residual stress field due to the mechanical indentation. On the basis of the results some consideration is formulated about generating micro-holes with one of the discussed ways.
查看更多>>摘要：This paper summarizes recent theoretical studies on the three-dimensional singular stress state at sharp notches in infinite (or large) plates of finite thickness subjected to in-plane loading. In general, such loading produces a number of singular states: in-plane singularities (normally described as K_I and K_(II) fracture modes and known as Williams' solution), singular states associated with corners and the out-of-plane singularity (K_O mode), which is generated due to the Poisson's effect. The latter mode has an interesting behavior and its intensity increases as a power function with the increase of the plate thickness when the notch is stresses in shear mode. From finite fracture mechanics considerations it is clear that at some certain thickness the out-of-plane singular mode will dominate over the fracture zone and with the further increase of the plate thickness will affect the strength of the notched plate, virtually reducing it to zero.
查看更多>>摘要：Effect of micaceous iron oxide epoxy coating on the microbiological influenced corrosion (MIC) behavior of the low alloy steel was studied. Samples uncoated or coated with micaceous iron oxide epoxy coating in sterile seawater and SRB solution was investigated by using electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and so on. A series of data was obtained. Results show that micaceous iron oxide epoxy coating protected the base material effectively duo to its excellent physical barrier property.
查看更多>>摘要：Advanced steels are designed and produced to be used in engineering applications in which thermo-mechanical fatigue could be a main factor in causing failure in components operating at elevated temperatures. In this paper thermo-mechanical fatigue properties of these steels are studied under the influence of creep and fatigue damage evolution. Development of different models and simulation techniques are reviewed to predict material behaviour. Numerical simulations are carried out to predict experimental tests on parent material notched bar specimens. Numerical predictions are introduced in advance of experimental test to assess the experimental test procedure. This is usually done to enhance the experimental result integrity and expectations. A local ductile damage development methodology is employed using the kinematic hardening criterion and compared to previously used strain hardening material property. The modelling on notched bar geometries is extended to geometries with cracks in which a local damage criterion will be used to predict virtual crack extension in compact tension specimens.
查看更多>>摘要：The use of the damage tolerance concept is growing in the design of civil engineering structures. The aim of this paper is to provide some guides to help designing anchorages according to the damage tolerance concept. The paper shows the importance of the small defects, idealized like small cracks, in the structural integrity of these elements. The Stress Intensity Factors (SIFs) induced by small cracks in an anchor head of post-tensioned strand anchorage system are calculated. The study includes the evaluation of the influence of the shape of the anchor head on the SIF. The numerical predictions are compared with experimental results of 1/2 scaled specimens of Poly-methyl-methacrylate (PMMA).
查看更多>>摘要：Nickel-titanium alloy are extensively used in engineering and biomedical fields for their excellent properties of shape-memory, super-elasticity and biocompatibility. Their fatigue performance has been attracted increasingly attention, because they are often used under cyclic conditions. In this paper, the ultrasonic fatigue behavior of nickel-titanium endodontic files under unconstrained condition has been studied using the self-designed ultrasonic fatigue testing equipment. The vibration and harmonious response properties of nickel-titanium endodontic files are also analyzed using finite element method. Experimental results show that the average ultrasonic fatigue life of nickel-titanium endodontic files under unconstrained conditions is more than 108. Fracture of the files always occurred at the position about 2 -3 mm near the file tip. Results of finite element analysis show that the maximum stress of the nickel-titanium endodontic files located at the position about 2-3 mm near the file tip, where is prone to generate fatigue cracks. The results of finite element analysis are consistent with the experimental results. The scanning electronic microscope (SEM) results show that the ultrasonic fatigue cracks always initiated at the surfaces of the files, where the secondary phases or impurities existed and induced fatigue cracks under repeated stress.
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