Papers by Keyword: Quasi-Static Loading

Abstract: Ti-6Al-4V titanium alloy is a high strength-to-mass ratio material common in a lot of engineering fields. Its surface oxide can guarantee the protection of the substrate from various corrosive media. Unluckily, this film can be scratched in presence of mechanical and chemical loads and for this reason the corrosion resistance can decrease. The Structural Mechanics Laboratory (SM-Lab) is carrying out a characterization of the alloy in different environments under quasi-static loading. In this paper, a summary of the outcomes of the investigation and the description of the fracture surface of a specimen with EDM notches quasi-statically tested in methanol is provided

Abstract: A variety of micro forming processes has been invented, and the size effects have become a research hotspot at home and abroad. Micro bending molds with different feature sizes were designed. Quasi-static tester loading and dynamic laser shock loading with soft punch for micro bending forming was studied by numerical simulation respectively based on ANSYS implicit analysis and LS-DYNA explicit analysis. The constitutive models of workpiece are bilinear kinematic hardening model and Johnson-cook model respectively. The effects of different loading conditions and feature sizes of the die on the forming depth, equivalent plastic strain and equivalent plastic strain rate were studied. The results of numerical simulation show that, with the increasing of feature size of the mold, the forming depth under two kinds of loading conditions shows a tendency to increase. In dynamic laser shock loading, the equivalent plastic strain and equivalent plastic strain rate of the key position of the bent part would decrease with the increasing of the feature size of the die. While in quasi-static loading, the opposite law is shown. The research shows that, the flexible micro-bending processes with different loading models showed similar size effect. However, compared with quasi-static loading, in dynamic loading, the strain of forming parts is more centralized, and there is a high strain rate and better formability of the workpiece.

Abstract: This paper describes mixture formulation of Ultra High Performance Fibre Reinforced Concrete (UHPFRC) with 2% of fibres by volume and its response to quasi-static and dynamic impact loading. The UHPFRC mixture was prepared using locally available constituents and no special curing or mixing methods were used for its production. In addition, the mechanical parameters of three other types of concrete, i.e. normal strength concrete (NSC), fibre reinforced concrete (FRC) and high performance concrete (HPC) is compared. The main properties assessed throughout the experimental work are compressive, flexural and direct tensile strength as well as response of tested concretes to impact flexural loading. The impact loading is produced by a vertically falling weight of 24 kg from the height of 1 m on concrete prisms. The strain rate increase corresponds to low-velocity impacts such as vehicle crash or falling rocks. Compressive strength of UHPFRC exceeded 130 MPa and its direct tensile strength was 10.3 MPa. This type of concrete also exhibited strain hardening both in flexure under quasi-static conditions and during impact. Based on the comparison of impact reactions, it was concluded that the resistance of UHPFRC to impact loading is superior compared to the referent types of concretes (NSC, FRC, HPC).

Abstract: Recently, building and other civil engineering structures are built with energy dissipating device in order to reduce the damages caused by earthquake. There are a number of seismic energy dissipating device and steel dampers are among many energy dissipation device which is widely used because they are easy for construction, maintenance and low cost. Shear panel damper (SPD) is a type steel damper that dissipates energy by metallic deformation or using hysteresis of material as a source of energy dissipation. Low yield point steel is a good material to be used as a hysteresis damper since it has excellent ductility performance. Nonlinear finite element analysis was carried out to predict the large deformation and hysteretic behavior of SPD using low yield point steel (SLY120) for different width-to-thickness ratio. In order to verify the analysis simulation, quasi-static loading was also conducted and from the comparison a satisfactory result was found.

Abstract: One of the signatures of the presence of cracks in a sample is the nonlinearity in its elastic response to an impingent ultrasonic wave. The Fourier analysis is often inadequate to monitor the evolution of nonlinearity, since the signal-to-noise ratio of higher order harmonics is very low. In order to overcome this drawback, we suggest an alternative procedure to extract nonlinearity indicators from a recorded ultrasonic signal, based on the amplitude dependence of the response of the system. The procedure is first described and then used to analyse the evolution of the nonlinearity due to cracks induced by a quasi-static loading in mortar samples. Our approach allows to distinguish the compaction phase from the micro-damage progression and the pre-rupture phases.