Key Engineering Materials Vols. 385-387

Abstract: Cast iron and steel conveying rollers used in hot rolling mills must be changed very frequently because conveyed strips with high temperature induces wear on the roller surface in short periods. This failure automatically stops the production line for repair and maintenance of conveying rollers. In this study a new type of roller is considered where a ceramics sleeve is connected with two short shafts at both ends by shrink fitting. Here, a ceramics sleeve provides longer life and therefore reduces the cost for the maintenance. However, for the hollow ceramics rollers, care should be taken for maximum tensile stresses appearing at both edges of the sleeve. In particular, because fracture toughness is extremely smaller compared with the value of steel, stress analysis for the roller is necessary for ceramics sleeve. In this study FEM analysis is applied to the structure, and the maximum stress has been investigated with varying the dimensions of the structure. It is found that the maximum tensile stress appearing at the end of sleeves takes a minimum value at a certain amount of shrink fitting ratio.

Abstract: Linear friction welding (LFW) is a solid state joining process for bonding of two flatedged, complex geometry components through relative reciprocating motion under axial (compressive) forces. Although the proof of principle has been obtained some time ago, recently a number of studies have been published aimed at optimising the joining operations to obtain best joint strength and reduced distortion and residual stress. The present paper is devoted to the study of linear friction welds between components made from aluminium alloy 2124 matrix composite (AMC) reinforced with 25vol% particulate silicon carbide (SiCp). Neutron diffraction was used to measure interplanar lattice spacings in the matrix and reinforcement, and to deduce residual elastic strains and stresses as a function of distance from the bond line. Significant asymmetry is observed in the residual stress distribution within the two components being joined, that may be associated with the difference in the microstructure and texture.

Abstract: For the effective utilization of recycled aggregate concrete (RAC), it is necessary to correctly describe its compressive stress-strain curve (SSC) in theoretical and numerical analysis as well as engineering design of RAC structures. The objective of this study is to establish a good mathematical model for SSC of RAC. Based on energy dissipation theory, the differential governing equation of SSC is deduced and a new mathematical model is obtained. The new model can well describe both hardening type SSC and softening type SSC. It can overcome the shortcoming of the traditional model. Finally, good agreements have been found between the new model and the experimental investigations.

Abstract: The objective was to quantify the variation of stress intensity factor to weld root flaw sizes in steel frame connections. Finite-element analyses were used to study fracture toughness in welded beam-column connections. Investigations of fracture behavior mainly focused on the standard pre-Northridge connection geometry. Finite element analysis was performed using the ANSYS computer program. Stress intensity factor was calculated through a J-integral approach. The parametric study was conducted to quantify elastic fracture demands as a function of beam geometries. Results show that stress intensity factor is not uniform and is the largest in the middle of beam flange. The breadth of beam flange has primary effect on ratio of equivalent stress intensity factors to average. The ratio is nearly linear with the increase of the breadth, and it increases with the increase of breadth of beam flange.

Abstract: This work presents the enhancement of a pseudo-numerical tool for fatigue crack growth investigations on integrally stiffened metallic panels. The model is based on an analytical approach that demands compatibility of displacement between skin sheet and stiffener. Since the basis model was presented before, the focus of the present work is on the incorporation of residual stress effects in order to improve simulation results of welded panel configurations that are manufactured by laser beam welding or friction stir welding and exhibit a significant amount of residual stresses. The necessary input parameters for the developed residual stress module are determined from experimental residual stress field measurements. Simulation results using the presented approach are compared with results from finite element simulations on a two stringer panel which show the good accordance of the base model as well as the capability of the tool enhancements to account for the crack retarding effect caused by residual stresses.

Abstract: Artificial neural network (ANN) is widely applied to the modeling of complex systems, which has become a common modeling method in the study of materials science. As the ideal candidates for high temperature structural materials, carbon materials are no doubt involved in fatigue loads, so the study on forecasting fatigue life is meaningful. In this paper, the electrical resistance at various fatigue cycles and level of applied stress of the materials under tensile fatigue loading has been detected, and regarded the fracture or fatigue cycles equal to 106 as fatigue life of carbon materials. On the basis of the electrical resistance value, the fatigue life has been forecasted by applied the ANN. The results indicated that the ANN could forecast the fatigue life of carbon materials well; finally, the applications of ANN in the study of material, such as properties prediction, damage prediction and failure detection were reviewed.

Abstract: As the ideal candidates for high temperature structural materials, carbon/carbon (C/C) composites are no doubt involved in fatigue loading. Therefore, the study on fatigue behavior is meaningful. In this paper, the research on fatigue behavior of C/C composites was reviewed and the characteristic of fatigue behavior was summarized. Some viewpoints for further investigations for the study on the fatigue behavior of C/C composites are also made in this paper.

Abstract: The evaluation of the stress singularities and generalised stress intensity factor (GSIF) for the case of an inclined surface crack terminating perpendicular to the interface between two orthotropic materials is considered. The knowledge of the regular and auxiliary solution allows evaluating the GSIF using the reciprocal theorem (Ψ-integral). A co-operating effect of a stronger and a weaker singular stress field for a crack impinging a bimaterial interface is investigated.

Abstract: The fatigue behavior of non-crimp-fabrics under different multi-axial loading conditions is presented, using a beneficial characteristic of the material, i.e. the fact that cracks may be detected by using an optical microscope. This allows to compare two different damage parameters, the crack density and the stiffness reduction over the life of the specimens.

Abstract: Fatigue test on a full scale panel with complex loading and geometry has been carried out using a tri-axial test machine specifically designed, built and located in the laboratory of the University of Naples. The aeronautical test panel was designed and manufactured by Alenia. The demonstrator is made up of two skins which are linked by a transversal butt-joint that is parallel to the stringer direction. A fatigue load was applied in the direction normal to the longitudinal joint, while a constant load was applied in the longitudinal joint direction. The demonstrator broke up after about 177000 cycles. Subsequently, a finite element analysis was carried out in order to correlate failure events; due to the biaxial nature of the fatigue loads, Sines criterion was used. The analysis was performed taking into account the different materials of which the panel is composed. The output shows good correlation between experimental data and numerical results, predicting the location on the panel exactly where the failure occurred.