Papers by Keyword: Rupture

Abstract: Effect of rare earth (RE) on creep rupture behavior of 316LN austenitic stainless steel (316LN steel) was investigated after crept at 700°C under the stress in the range from 125MPa to 200MPa, by the optical microscopy (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The results show RE addition in 316LN steel increased the creep rupture ductility at high stress, but reduced the creep rupture ductility at low stress. Under 200MPa, RE addition increased the creep rupture strain of 316LN steel from 0.558 to 0.787 but the creep rupture strain after crept under 150MPa was decreased from 0.875 to 0.566. The fracture mode of 316LN steel was also apparently impacted by the RE addition. The typical ductile fracture feature of homogeneous dense dimples was obviously observed in NRE steel after crept rupture under all stresses. While in 32RE steel, small amount of intergranular fracture fractographs under low stress appeared instead of partial dimples under high stress. Moreover, it is noted that RE addition in 316LN steel promotes to precipitate a great number of fine Laves particles within grains. These Laves particles strengthening the matrix resulted in the strain concentration on grain boundaries, which might sensitively induce crack initiation on grain boundaries during long-term creep under the low stress.

Abstract: The effect of point defects on the shear rupture resistance in titanium aluminide is investigated by the density functional theory and pseudopotential methods. Vacancies, as well as substitution atoms – tungsten and chromium were considered as points defects. The shear was simulated in the(111) slip plane for two directions, namely [110] and [11-2]. It is shown that for a {111}<110> sliding system, vacancies significantly reduce the shear resistance. However, when alloying element occupies a titanium vacancy, it can partially compensate for this negative effect.

Abstract: The criteria for the assessment of the form change in the process of direct profiling of workpieces , applying the stretching method with a rupture are developed, methods for their calculation are proposed with allowance for the volume of the redistributed metal and energy costs for deformation. The nature of the functional connection of these criteria of shape change assessment with the work of deformation is determined.

Abstract: The object of this study is to highlight one the most encountered problems in the sheet metal forming. Cases of rupture on the mild steel sheet were recorded in a deep drawing workshop, during the forming operation of the wheelbarrows. The phenomenon appearance, led us to carry out a study of the material behavior during the metal forming. A characterization of the material is proposed and 3D simulations of the forming operation were performed on the finite element code Abaqus/CAE Explicit. The objective is to highlight the influence of the different deep drawing parameters on the sheet behavior during the deformation, especially the holding force, the die radius, the coefficient of friction between the contact surfaces and the punch velocity.The results are summarized in a representation of the strain curves in the three directions of the drawn part at the end of deep drawing operation, localization of the sheet areas which present a risk of tearing and the proposals to avoid this phenomenon depending on the variation of the operating parameters.

Abstract: In this paper, the sheet hydroforming process of 2A12 aluminum alloy with uniform die cavity pressure on to the blank is proposed and investigated both primarily through the finite element method (FEM) and experiments. The influence of the die cavity pressure curve on the quality of the products was explored and the measures to promote the sheet formability were discussed. The results from the studied case indicate that the profile of the cavity pressure was one of the fundamental parameters directly related to the product's quality and precision. Excessive or insufficient initial pressure is not conducive for the reduction of wall thickness thinning and guarantee of wall thickness uniformity. And the wall thickness thinning is reduced and the thickness evenness is improved by increasing the maximum cavity pressure within a proper range. Moreover, an optimum cavity pressure curve generated by the numerical and experimental methods was properly applied in forming the aluminum alloy part without rupture and with slight wrinkle in the flange area. The study demonstrates that the results of simulations based on the identified parameters were in reasonable agreement with those from experiments.

Abstract: Skin laceration injury caused by a penetration of small curvature edge frequently occurs in a domestic accident. An assessment method for this injury is necessary in order to develop a safer manufactured product. To assess the risk of skin laceration injury in a penetration accident, a skin simulant made from silicone rubber was proposed. However, mechanical responses of this skin simulant under dynamic penetration loading have not yet been investigated. In this study, a drop weight penetration test device was developed in order to simulate penetration accidents under impact velocities of over 1 m/s. The device was then used for investigating the dynamic responses of skin simulant against several blades with different tip curvature radii. Load, penetration depth, impulse and energy at rupture were then determined from the test results. Load and penetration depth at rupture increased with the increase of tip curvature radius of the blades. Furthermore, the drop weight test result showed larger response compared to the quasi-static test result which might be caused by the viscous effect and the polymer characteristics such as cross-linking of the skin simulant.

Abstract: A new model is introduced, for predicting the nonlinear behavior of the concrete until the rupture. The non-linear behavior of the concrete is taken into account under monotonic load verifying the principles of the mechanics damage [1] and the concepts of the mechanics of the fracture, using the foundations of the continuum mechanics of materials [2]. The nonlinear mechanical behavior of the concrete in unidirectional is described by two laws (Sargin [3] for the compression and Grelat [4] on the tension). By introducing two variables of damage applied in unidirectional respectively in tension and in compression (Y. Bouafia , R. Smahi, and al., (2014)) [5]. Their combination with the laws of the continuum mechanics of materials (Hooke’s low generalized) [2], and the theory of the mechanics damage (theory of the isotropy of the damage, and principle of the equivalent deformation), brings us to a law of variation of the damage in three-directional applied in bidirectional. In addition, if the variation of the Poisson’s ratio of concrete in unidirectional compression has attracted the interest of several researchers we can cites: (Sami, A., Klink, 1975 [6], Murray D.W. 1979 [7], Niels Saabye ottosen, (1980) [8], Atheel E. Allos., L.H.Martin, (1981) [9], Ramtani.S, Y. Berthaud , J. Mazars, (1992) [10] and Ferretti, E., (2004) [11]. For the three-dimensional, we can mention: Chen 1982 [12], Guo 1997 [13], Zhu 1998 [14], Hyuk-Chun Noh, Hyo-Gyoung Kwak 2006 [15] and Ding Faxing Yu Zhiwu 2006 [16]. Confrontations of the calculations with experimental results (behavior of the concrete in biaxial compression and tension) have allowed to describe and to follow the real behavior of the concrete.

Abstract: This article will examine the effect of the knots distribution on strength of glued laminated timber beams. A finite element model was made to simulate glued laminated timber beams with defects (knots) to simulate and predict behavior in areas containing knots while bending. This model was then compared with results from static bending test of glued laminated timber beam. The initial position of the rupture was then compared with FEM model [6], so the influence of knots on strength could be determined.

Abstract: The rupture and its several influence factors on the short crossbeam of sieve case during square plansifter running are investigated. Aimed at the system consisting of a square plansifter and some suspenders, the FEM is employed to establish structure dynamic model for obtaining dynamic response. According to the contrast of the vibration data of sieve body in experiment and the displacement response from FEA, the finite element model is modified. Results show that the position where the maximum stress happens in FEA and the position of actual rupture are the same. Furthermore, the influence of various factors on the maximum stress of three dangerous positions are computed and analyzed. The results presented in this paper possess an important reference value to structural improvement and dynamic optimization of square plansifter.

Abstract: The mechanical behavior of thin sheets of aluminium alloy 6016, of thickness 1.14 mm, was investigated in unconstrained bending, with or without a tensile pre-strain. In the case of bending without pre-strain, no rupture was observed. Therefore, a tensile pre-strain, ranging from 0.19 up to 0.45 (longitudinal strain), was applied prior to bending. The highest pre-strain values were reached within the necking area. Tensile tests on rectangular samples were performed, then reduced samples were cut out and submitted to bending. A Digital Image Correlation (DIC) system was used to measure the maximum local strains reached during both tests. The evolution of the applied load on the bending tool versus its displacement showed that a rupture in bending was obtained for tensile pre-strains higher than 0.25, as evidenced by a load drop. These results showed that very high strains can be reached in bending, which is consistent with previously obtained numerical results.