Papers by Keyword: Compact Tension Specimens

Abstract: Thin compact tension specimens made of direct quenched ultra-high strength steel were tested under constant rate uniaxial tensile load. The length of the crack was monitored using optical microscopes on both sides of the specimens during the fatigue pre-cracking (using a chevron V-notch). Deformations during the crack lengthening were recorded by a full-field measurement technique using a set of digital cameras to check the effect of side grooves on reduction of surface deformation. The Specimen without side grooves showed a high level of plasticity, thickness reduction, and crack growth along a deviating path. In addition, the fracture surface showed excessive failure along the inclined plane. The presence of side grooves, however, led to the decrease of the maximum applied force at final fracture while the force prior to crack tearing was almost the same as the specimen without side grooves. Grooves significantly reduced the inclination of the fracture plane and plastic deformation due to removal of low stress triaxiality on the surface. They led to the fracture along a straight path and approximately even surface which makes them beneficial especially when compliance method is used in plane stress fracture tests.

Abstract: The behavior of concrete structures is strongly influenced by the loading rate. Compared to quasi-static loading concrete loaded by impact loading acts in a different way. First, there is a strain-rate influence on strength, stiffness, and ductility, and, second, there are inertia forces activated. Both influences are clearly demonstrated in experiments. For concrete structures, which exhibit damage and fracture phenomena, the failure mode and cracking pattern depend on loading rate. Moreover, theoretical and experimental investigations indicate that after the crack reaches critical speed of propagation there is crack branching. The present paper focuses on 3D finite-element study of the crack propagation of the concrete compact tension specimen. The rate sensitive microplane model is used as a constitutive law for concrete. The strain-rate influence is captured by the activation energy theory. Inertia forces are implicitly accounted for through dynamic finite element analysis. The results of the study show that the fracture of the specimen strongly depends on the loading rate. For relatively low loading rates there is a single crack due to the mode-I fracture. However, with the increase of loading rate crack branching is observed. Up to certain threshold (critical) loading rate the maximal crack velocity increases with increase of loading rate, however, for higher loading rates maximal velocity of the crack propagation becomes independent of the loading rate. The critical crack velocity at the onset of crack branching is found to be approximately 500 to 600 m/s.

Abstract: Beryllium (Be) is susceptible to introduce stress because it is a brittle metal with a high elastic modular. The compact tension (CT) specimens of beryllium were designed to determinate stress and fracture behaviors. Stress distribution near notch in CT beryllium was measured by the combination of an X-ray stress analysis and a custom-designed load device. The results show that local stresses near notch tip are much higher than those on other area. Thus, stress concentration lead the CT specimens fracture along the notch direction. Residual stresses due to machining are remained. A finite element ( FE ) calculation on the same loaded geometry was made, and the result is agreement with the measured stress distribution near notch.