Key Engineering Materials Vols. 452-453

Abstract: A thermomechanically coupled constitutive model for finite strain elasto-plasticity is formulated and numerically implemented. The model gives a physically sound description of an initially austenitic material influenced by martensitic phase transformation. The heat dissipated by plastic slip deformation and by phase transformation is allowed to influence the material behavior and appears as a key influencing factor on the growth of the martensitic phase. The model is calibrated using a common stainless steel as prototype material, allowing numerical simulations of crack propagation to be performed. Alterations of the crack growth behavior are observed as different simulation scenarios are compared.

Abstract: Cavitation normally causes severe damage in hydraulic machinery such as pumps and turbines by the impact produced by cavitation bubbles collapsing. Although cavitation is known as a factor of erosion, Soyama et al. succeeded in utilizing impacts of cavitation bubble collapsing for surface modification by controlling cavitating jet in the same way as shot peening. The local plastic deformation caused by cavitation impact enhances the fatigue strength of metallic materials, and the surface modification technique utilizing cavitation impact is called “cavitation peening (CP)”. It is well known that the peening improves fatigue strength by introducing compressive residual stress on the surface, but little attention has been paid to the behavior of fatigue crack growth of the material which was modified by CP. In the present study, the fatigue behavior of austenite stainless steel with and without CP was evaluated by a plate bending fatigue test, and the results revealed that the compressive residual stress introduced by CP suppresses fatigue crack growth rate by 70 % compared to that without CP.

Abstract: Fatigue life of smooth specimens is approximately controlled by the growth life of a small crack. This means the growth behavior of small cracks must be clarified to estimate the fatigue life of plain members. However, there are few studies on the growth behavior of small cracks in ultrafine grained (UFG) metals. In the present study, fatigue tests for UFG copper have been conducted. The formation behavior of shear bands (SBs) and growth behavior of a small crack have been monitored to clarify the effect of SBs on the growth behavior of a major crack.

Abstract: This paper presents methodologies for fracture analysis and fatigue remaining life prediction of concrete structural components with and without accounting for tension softening and size effects. Stress intensity factor (SIF) is computed by conducting finite element analysis (FEA) and compared with that obtained by using analytical approach. The domain integral method has been used to calculate the strain energy release rate (SERR) and SIF by post-processing the FEA results. Nonlinear fracture mechanics principles (NLFM) have been used for crack growth analysis and remaining life prediction. Details of size effect in the computation of SIF and remaining life prediction have been presented. Size effect has been accounted for by modifying the Paris law, leading to size adjusted Paris law. Numerical studies have been conducted for fracture analysis, crack growth studies and remaining life prediction. The predicted remaining life values with the combination of tension softening & size effects are in close agreement with the corresponding experimental values available in the literature.

Abstract: This paper presents methodologies for damage tolerance evaluation of tubular T- and Y-joints by using linear elastic fracture mechanics (LEFM) principles. The damage tolerance evaluation is in terms of crack growth analysis and remaining life prediction of tubular joints. Stress intensity factor (SIF) for T-butt plates which can be used for computation of SIF for tubular joints has been evaluated as per BS: 7910. It is observed from the literature that the expressions given in BS: 7910 for computation of SIF have not been used for remaining life prediction of tubular joints. In this paper, these expressions have been used for analytical prediction of remaining life of tubular T- and Y- joints subjected to constant amplitude loading (CAL) and variable amplitude loading (VAL). Wheeler residual stress model has been employed to represent the retardation effects due to tensile overloads. It is observed that remaining life predicted for T- and Y-joints under CAL are found to be in good agreement with those of experimental values reported in the literature. In the case of VAL, it is observed that crack growth retardation increases with increase of OLR resulting in higher predicted remaining life. It has also been observed that the predicted remaining life is influenced by the number of OLs and occurrence of OL. Early occurrence of OL causes the higher remaining life compared to later OLs.

Abstract: Freeze-thaw damage is one of the most representative damages in concrete durability. In this study, rapid freezing and thawing tests were conducted to investigate the freeze-thaw resistance and analyze the correlation of the evaluation indexes of lightweight aggregate concrete with different water-cement ratios. The high correlation was confirmed between the length change and relative dynamic modulus of elasticity of lightweight aggregate concrete. The relative dynamic modulus of elasticity decreased with the increase of concrete length. However, the correlation was different according to the water-cement ratio values of lightweight aggregate concrete. The higher water-cement ratios, the lower expansion values of lightweight aggregate concrete when the relative dynamic modulus of elasticity decreased to the same degree under freezing and thawing action.

Abstract: In order to research the stiffness degradation mechanism of RC T-beam under the condition of different damage and get the influence law of damage degree on dynamic characteristics of single beam, the dilapidated static and dynamic test on four pieces of RC simple T-beams is explained in the paper. Under different degree of damage these parameters of four pieces of RC simple T-beams with two kinds of reinforcement ratio, such as crack, mid-span deflection, basic frequency, dynamic stiffness, static stiffness are measured. The frequency and stiffness variation of RC T-beam is obtained. The functional relationships of T-beam between ratio of static stiffness to dynamic stiffness and load ratio , the frequency ratio and load ratio were established. Furthermore the numerical simulation calculation on test results is made by the finite element analysis. According to the above research, the damage mechanism and frequency variation of RC T-beam under vertical load are summarized.

Abstract: This document explains and demonstrates experimental activity on 4 scale-models of elevated pile cap foundation belonging to a long span continuous bridge. The foundation was composed of 9 piles, pile cap and pier and the special soil box was built to consider soil-pile-superstructure interaction. According to the test result, the development rule of the failure mode, the failure form, the load-displacement hysteretic loops and the plastic hinges mechanism etc. for specimens were summarized. Moreover, the energy dissipation capacity and the viscous damping ratio were gained. The test also provided the data to quantitatively assessment the positive effect of steel protective pipe for RC pile. Fiber beam-column finite element model considering the modified Park-Ang damage index was built in OpenSees. This damage model was proposed to consider the loading path, the pronounced pinching effect of concrete and bond-slip of the reinforcing bars in the paper. In calculation strength degradation and stiffness degradation effects were both embodied. The skeleton curves of test and numerical analysis are both consistent by comparing.

Abstract: This paper presents the results of experimental tests carried out on steel fibre reinforced self-compacting concrete (SFR-SCC) beams without stirrups. Sixteen beams are cast using four mixtures of SCC with different steel fibre content, while the longitudinal reinforcement is kept constant in all test members. The beams are subjected to four point bending tests at a shear span-to-depth ratio of 2. The ultimate shear stress is recorded, as well as the crack pattern and the mid-span beam deflection. Test results show that as fibre content increases, higher ultimate shear stresses are achieved. When fibres are included, test members exhibit an increase in ductility and a more extensive crack pattern is observed. The experimental values of the ultimate shear stresses are also compared with theoretical values as given by empirical expressions in literature.

Abstract: Some authors proposed to combine a torsional loading of cylindrical specimens with surface semi-elliptical cracks (the principal axes along the axial direction) with superimposed static axial compression in order to eliminate kinking or branching of shear cracks from the shear plane. To authors’ knowledge, however, no precise numerical analysis of such a loading configuration is currently available. The aim of this article is to calculate stress intensity factors KI, KII and KIII along the semi-elliptical crack front using the ANSYS code. The problem is solved for a semi-circular crack front and various crack inclination angles. The results reveal that the compressive loading cannot eliminate the branching process. The inclination of the crack plane induces a rather high opening mode which means that the microscopically tortuous fatigue cracks observed in experiments grew under mixed-mode I+II+III.