Key Engineering Materials Vols. 535-536

Abstract: The paper presents experimental results of tests carried out at room temperature on power engineering steel: 10H2M (11CrMo9-10) using thin-walled tubular specimens under biaxial stress state. The loading programme comprised different types of deformation, i.e. monotonic tension and cyclic torsion in the form of symmetric or asymmetric step-increasing strain amplitude. The main task of the paper was focused on investigation of an influence of the cyclic loading parameters on tensile curve variations. The magnitudes of axial strain and cyclic shear strain amplitude were small and did not exceed 1%. An analysis of the results showed a significant reduction of the axial stress (even equal 90% for the torsional amplitude ±0.8%, in both cases of cyclic loading). An influence of torsion frequency on the tensile stress curve was discovered within the range from 0.005Hz to 0.5Hz.

Abstract: To clarify the essential deformation characteristics of silica-filled rubber, we construct the finite element homogenization models of silica-filled rubber with newly proposed nonaffine molecular chain network model of rubber. These models can reflect the generation of complicated inter-fillers connecting phases where the characteristics of rubber are intricately changed depending on the volume fraction of silica coupling agent and relative size of particles and their location. The results obtained clarified the essential physical enhancement mechanisms of deformation resistance and hysteresis loss for rubber filled with silica with different distribution patterns under diffrent rate of deformation. The volume fraction of coupling agent essentially affects the deformation behavior of silica filled rubber which suggests the high controlability of the material characteristics of silica filled rubber as compared with carbon black filled rubber.

Abstract: The aim of this study is to investigate the cyclic behavior and the fatigue life of an industrial α/β brass through mechanical tests and microstructural observations. The main obtained results are about the cyclic behavior of the alloy and the characterisation of fatigue life in connection with the evolution of the microstructure. Cyclic tensile test shows a great and rapid evolution of the isotropic hardenig during cycling.

Abstract: The accumulation of cyclic plasticity in bond coat (BC) is a key factor controlling the displacement instability of the thermally grown oxide (TGO) in thermal barrier systems. The cyclic plasticity is affected by the component material properties, which vary observably with the service temperature. A numerical model with the behavior of creep and thermal growth in TGO under thermal cycling is used to explore the effect of temperature-dependent properties on cyclic plasticity in BC. The influence of temperature-dependent Young's modulus of thermal barrier coating (TBC), TGO, BC and substrate, thermal expansion coefficient of TBC, BC and substrate, and the yield strength of BC on cyclic plasticity in BC is discussed respectively.

Abstract: Based on a simplified equivalent 2-D plane strain finite element model, the bending fretting fatigue process of 316L stainless steel is simulated numerically by ABAQUS code. In this simulation, the effect of ratchetting on the fretting fatigue process is discussed by implementing an advanced cyclic elasto-plastic constitutive model for cyclic hardening materials into ABAQUS code as a user material subroutine (UMAT). From the numerical simulation, the effect of bending loads on the bending fretting fatigue of 316L stainless steel is addressed, and then the failure lives are predicted by using Smith-Watson-Topper critical plane criteria. Comparison with the corresponding experiments shows that the predicted results are in good agreement with the experimental ones.

Abstract: This work is devoted to a survey of the ratcheting phenomenon and follows the study presented in [1]. Two current austenitic stainless steels 304L and 316L are considered and tested under cyclic stress and strain control at 350°C. Under stress control ratcheting seems very small under proportional as well as non-proportional stress control. The elastic shakedown steady state exhibited by both materials may be explained by their capabilities to develop very significant cyclic hardening (especially isotropic) at 350°C.

Abstract: Fatigue behavior of reinforced concrete (RC) beam can be improved by externally bonded fiber reinforced polymer (FRP). However, propagation behavior of a crack on the RC beam will have serious effect on the fatigue life of the beam strengthened with FRP. In this paper, a finite element (FE) procedure was developed to analysis the stress intensity factor (SIF) of the main crack and an experimental study was conducted to investigate the propagation rate of the main crack of the RC beam strengthened with carbon fiber laminate (CFL) under cyclic bending load. The FE analysis results show that the SIF near the main crack tip increases at the beginning and then decreases with the fatigue crack propagation. When relative crack length α is equal to 0.3, the SIF is maximum. When α approaches 0.75, the SIF approaches zero. A total of 3 RC beams strengthened with CFL were tested. The experimental results show that it is possible to divide the process of the crack propagation into three distinct phases, including crack initiation and then quickly propagation, stable propagation and then rest and unstable propagation. A semi-empirical equation based on the Paris Law was developed to predict the crack propagation rate.

Abstract: The texture of rolled sheets is known to vary with depth from the surface to the center due to inhomogeneous deformation, which can be caused by a characteristic deformation zone geometry and friction between materials and rolls during rolling. In order to study the deformation and recrystallization (Rex) textures of the surface layers of Al and Cu sheets cold rolled without lubrication, 5 Al sheets were stacked and rolled by 88% and 4 Cu sheets were stacked and rolled by 93% in 4 passes at room temperature. The surface layers separated from the rolled sheets were annealed for 1 h at 500 °C for Al and at 550 °C for Cu. The deformation textures of the surface layers were characterized by different shear textures, which gave rise to very different Rex textures.

Abstract: Electrospinning technology was used to obtain non-woven sheets made from fine fibres in a controllable diameter range from 50 nm to 3 µm. Poly(ethylene-co-vinyl alcohol), a large molecule polymer was chosen to make the fibres for its biodegradable and biocompatible properties. The thin sheets obtained were tested in uniaxial tension for their mechanical properties in view of the potential use as wound dressings. It is found that the sheets show a mild hardening behavior with extensive elongation and necking before failure in multiple fractures at random locations. Due to the random orientation of the continuous fibres in the sheet, detachment, shear, straightening and twinning. etc., occur amongst fibres to different extends at the same time. The Young’s modulus and the yield stress (at 0.4~0.5% proof strains) are predominately affected by fibre diameters, and are largely insensitive to strain rate over the range tested.

Abstract: A series of deep indentation and uniaxial compression tests of closed-cell aluminum foams at room temperature as well as elevated temperatures were conducted. A flat-ended punch (FEP) was used in the indentation tests. Cross-sectional views of the specimens after tests show that the deformation is roughly confined to the material directly underneath the indenter with slightly lateral spread. It is found that plastic collapse strength and energy absorption of the specimens are temperature dependent in both loading conditions. Tear energy of the foam in FEP indentation depends on the indentation depth and temperature.