Key Engineering Materials Vols. 488-489

Abstract: The aim of this paper is the application of two methods for notch fatigue life assessment, methods which are based on finite element analysis: the theory of critical distances and the volumetric method. Firstly, un-notched and notched specimens (for three different geometries) were tested in tension under constant-amplitude loading. The use of theory of critical distances (TCD) to predict the notch fatigue life involves the determination of the material characteristic length L based on experimental results obtained for the un-notched and one type of notched specimens. For the others notched geometries, based on linear-elastic finite element analysis, the fatigue strength is predicted using the TCD. In order to apply the volumetric method, elastic-plastic stress field around notches are considered and notch strength reduction factor are determined. Finally, the predictions of the two methods were compared with experimental fatigue data for notched specimens.

Abstract: A preliminary sensitivity examination of the ductility exhaustion based creep damage prediction model, currently used in the R5 high temperature assessment procedure, showed that material property inputs had significant effects on damage prediction. In the present work, the link between the microstructural factors and the susceptibility to inter-granular high temperature creep failure is considered. The latter was judged to be associated with the low creep ductility. Here, the longitudinal section of a creep specimen and the fracture surface were examined. Auger electron spectroscopy was used to investigate the grain boundary composition in this specimen, which failed after a creep test of 1038h at 550°C under a triaxial stress state. The present results demonstrate that there is a possibility to correlate the susceptibility to high temperature inter-granular fracture from the low temperature fracture investigations. Finally, the susceptibility of the pre-treated 316H stainless steel to inter-granular high temperature failure and the contribution to the creep damage model are briefly discussed.

Abstract: Fretting fatigue occurs when two contact bodies undergo small oscillatory relative motion due to cyclic loading. It leads to fretting damage, which reduces the service life of the bodies in contact. This can be explained by the high stresses generated at the contact surface between the two bodies. Therefore, numerical analysis, such as Finite Element Analysis (FEA), would be useful to understand the fretting fatigue phenomenon and to investigate techniques to reduce its effect on fatigue lifetime of mechanical components. In this paper, FEA of fretting fatigue Aluminum specimen is carried out in order to study the stress distribution and crack initiation location. Two commercial FEA packages, namely ANSYS and ABAQUS are used to analyze the specimen. The stress distribution along the contact surface between the two bodies obtained using both codes is compared and analyzed.

Abstract: Rupture dynamics in reinforced elastomers is a much more complex process than in pure elastomers due to the intrinsic heterogeneous mixture of a rubber matrix with filler particles at submicronic scale. In the case of natural rubber, an additional source of heterogeneity is the strain-crystallization effect. How rupture dynamics and crack path are affected by filler particles and strain-crystallization is still a matter of debate. Actually, understanding how rupture dynamics and crack path are correlated to each other is probably an important key in order to improve long time resistance of reinforced rubbers.

Abstract: Polycrystalline diamond (PCD) materials have a variety of applications, mainly as cutting tools for machining non-ferrous metals and non-metallic materials. A significant application of PCD is in oil and gas industry for rock drilling operations. Other important areas, such as mining, have yet to reach their full potential. These cutters/tools are subjected to high operating temperatures, impact loads and abrasive wear during these operations, which may lead to their sudden failure. An advantage of these materials is that their structure and composition can be engineered to return properties required for specific applications and operations.

Abstract: The Clemente Bridge is a multi-span masonry arch bridge built during the 18th century on Savio River in Cesena. The aim of this paper is to assess its static capacity under live loads prescribed by Italian Standards in force. The analysis is performed employing RING 3.0, a computational tool based on Limit State Analysis. This method allows to individuate the minimum adequacy factor, that is the multiplier on vehicle loads required to cause collapse. In this way, a first assessment on the bridge safety can be obtained.

Abstract: It appears that sudden change of loading such as shock wave impinging on underground structures, which is mostly linked up with an extreme increase of temperature, causes immense disasters, which involve loss of human lives, heavy machine damage, long-lasting traffic troubles, decreasing of bearing capacity of the structural system, etc. A combination of shock wave due to both the elevated temperature accompanying explosion leads to cracking of the bearing system of underground openings, for example to cracking of concrete lining, i.e. to reduction of thickness of the bearing structures, etc. It has been previously proved that the free hexagon method serves for identifying the damage in the bearing system of underground structures very well. The dynamical influences have to be also emerged if extreme raise of temperature and explosion are involved in this problem; formulation is briefly mentioned and the results from numerical simulations are presented. It will be shown that the superheated vapor interacting with shock and temperature waves caused by the point charge inside of the underground open space may cause extensive occurrence of fissures on the surface exposed to the external loading envisaged.

Abstract: The article presents application of non destructive testing method based on the pulse heating infrared thermography used to detect material anomalies for the case of glass reinforced polymer structures. The goal of presented research, based on the thermal gradient approach, is to establish the procedure capable of filtering out anomalies from other thermal influences caused by thermal reflections of surrounding objects, geometry influences and heat flows for observed object.

Abstract: Shape memory alloy (SMA) reinforced composites have been widely used in aerospace engineering fields. In this paper, four basic assumptions were presented to simply the research model based on the Eshelby’s equivalent inclusion method and Mori-Tanaka scheme. Based on the three-phase equivalent system and two-step equivalent process, the effective elastic modulus and thermal expansion coefficient of unidirectional random distribution short SMA fiber reinforced composites were derived. The tensile mechanical properties of composites with fiber volume fraction (15%), size (L=3, D=1; L=5, D=1), and number (N= 30, 50), were simulated using software ANSYS12.0, and discussed the failure mode of the composites.

Abstract: In this paper, the sandwich structure which is consist by the aluminum foam core and CBF(continuous basalt fiber) composite plate is tested by the static and dynamic mechanical property under confining pressure, and the confining pressure experiment is done through add cylindrical tube to the sandwich structure circular specimens. The static mechanical property is tested by WDW3100 electronic universal testing machine, and its dynamic mechanical property is tested by the SHPB(Spilt Hopkinson Press Bar) device, Besides, the strain rate effect of this sandwich structure under confining pressure is tested too, From the experiment results we can see the static and dynamic mechanical properties of confining and no confining results is very different, and this study will provide references for further numerical simulation and damage studying of this kind of sandwich structure.