Abstract: A fracture criterion for sheet metals subjected to draw-bending is investigated using the concept of forming limit stress criterion. The test material used is a 1.0-mm-thick ultralow carbon steel sheet. Draw-bending experiment of a wide specimen is performed for a die profile radius of 4mm. A specimen undergoes bending-unbending under tension when passing over the die profile radius. The drawing speed was set to 5mm/s. The magnitude of true stress when a specimen fractured has been precisely determined from the measured data of a drawing force and the cross sectional area of the draw-bent specimen after fracture. Moreover, multiaxial tube expansion tests of the test material are performed to measure the forming limit stress of the test material under plane strain tension. It is found that the is larger than by approximately 10 %. Therefore, it is concluded that the forming limit stress criterion is effective as a fracture criterion for a mild steel sheet subjected to draw-bending.
Abstract: In this paper, the interference between arbitrary shaped 3D planar crack and cavity existing in the vicinity of the crack front is evaluated. It is assumed that the treated region is unbounded and subjected to uniaxial tension at infinity. The interaction between crack and cavity is treated by body force method. The surface of the crack and cavity is modeled by number of small triangular elements and the density of body force and weight function of the force doublet is assumed at a constant on each triangle. Numerical stress analyses are examined by changing the radius of cavity and the distance between the cavity and crack front systematically. Numerical results are presented for the stresses along the centerline between cavity and crack. To validate the current analysis, numerical results are compared with the results in the literature and found good agreement.
Abstract: In this paper, the symmetric Galerkin boundary element method (SGBEM) will be developed and applied for boundary value problems with layered and fiber reinforced piezoelectric representative volume elements (RVE) and real macroscopic structures. Mechanical and electric loadings are considered to determine the effective material properties. For this purpose, the resulting boundary value problem is formulated as boundary integral equations (BIEs). The Galerkin method is applied for the spatial discretization of the boundary to solve the BIEs numerically. The required surface derivatives of the generalized displacements are computed directly with a boundary integral equation. Numerical examples will be presented and discussed to show the efficiency of the present SGBEM and the influence of the fiber variation on the effective material properties.
Abstract: Deterioration of reinforced concrete infrastructure such as bridges, tunnels, and buildings represents one of the major challenges currently facing developed countries. While engineering tools and methods for structural modelling and design of new reinforced concrete infrastructure are mature, methods and tools for modelling decades-long deterioration and maintenance are much less developed. In this paper, a multi-physics and multi-scale modelling approach for structural deterioration of reinforced concrete components due to reinforcement corrosion is presented. The multi-disciplinary modelling approach includes physical, chemical, electrochemical, and fracture mechanical processes at the material and meso-scale, which are further coupled with mechanical deterioration processes at the structural scale.
Abstract: The chip formation mechanism in orthogonal cutting is a phenomenon that attracts the attention of many researchers. This paper investigates experimentally the orthogonal cutting of Ti6Al4V at different cutting conditions aiming at the understanding of the chip formation mechanism. Serrated chip formation is obtained during orthogonal cutting of Ti6Al4V in a wide range of cutting speeds. The results are analyzed in order to extract useful indices relevant to chip geometry, as the adiabatic zone angle and other dimensions that describe the serrated chip. The cutting forces and the acoustic emission are measured. Finally, by the aid of 3D Computed Tomography (CT) the chip morphology is analyzed to better understand the segmentation process.
Abstract: In this study, ductility of members with ultra-high performance concrete was investigated using moment-curvature analysis for the verification of safety under large deformation of ultra-high performance concrete structural members. For the analysis of members with ultra-high performance concrete, mathematical stress-strain model was selected among the results conducted by other researchers on the compressive and tensile behavior of high strength concrete and fiber reinforced concrete. According to the investigation on ductility of members with ultra-high performance concrete, decrease of ductility was observed with increase of tensile strength of concrete under the same reinforcement ratio. Members with 2~3% of reinforcement ratio, which usually be used in the field engineering, show the decrease of ductility with increase of fiber volume fraction. As a results of parametric study, limitation of maximum reinforcement ratio ( or limitation of net tensile strain ) suggested by current design code is not safe when using ultra-high performance concrete.
Abstract: If the dimensioning methods of new structures are well controlled, the forecast of the seismic levels for which an existing building resists is a problem much more difficult to define. Their behavior and their comportment are completely unknown. The modeling of deteriorating hysteretic behavior is becoming increasingly important. With numerical integration procedures and the spectacular progress of computers, it is possible to predict the nonlinear behavior of reinforced concrete structures by using material rheological models during and after an earthquake. The objective of this research work is to develop a rheological model which allows digital nonlinear simulations (material) of structural systems excited by cyclic loads taken from seismic sources such as they are presented in reality, meaning in the form of digitalized accelerogram. This procedure requires a calibration dictated by particular transformations for the case of RC structures under this type of excitation in all points of the system and at every moment during the lasting of the signal. Besides, macrofibers models offer a satisfactory approach for analyzing all RC structures by taking into account various generated phenomena.
Abstract: Objectives: The mechanical characteristics of bone cement depend on the chemical composition, mixing technique, polymerization period and temperature. Additionally, the shape of the cement mantle can also lead to variations in the mechanical properties of the material, as thicker walls are significantly more non-homogeneous and less permeable for the body fluids. This paper presents experimental tensile tests on bone cement focused on the study of the influence of the test specimen shape on the obtained results.Methods: High viscosity bone cement, produced and supplied as polymer powder and monomer liquid portions was used. The mixed cement was inserted during the working time into two types of silicon molds: one with the shape and size according to ISO 527 (“dogbone” shape with rectangular cross section area) and other with the shape and size according to ASTM F 2118 (“dogbone” shape with circular cross section area). Both types of test specimens have approximately the same value of the cross sectional gauge area. All samples were polished with grit abrasive paper in the longitudinal direction and soaked in phosphate buffered saline (PBS) solution. The specimens were subjected to a tensile test on a hydraulic machine. To avoid the occurrence of critical stress areas on the specimen, special fixing devices were manufactured.Results and conclusions: The stress–strain curves of all specimens tested exhibited similar linear elastic regime followed by brittle fracture. However, different values of the ultimate tensile strength and elastic modulus of tested samples were recorded.
Abstract: Aluminium clad steel reinforced cables are widely used in long distance electrical energy transport. Under the influence of weather conditions, the conductors are subjected to additional stress, which may lead to accelerated deterioration and premature breakage. This phenomenon depends much on contact mechanics. Due to the rough geometry of real mechanical surfaces, the elastic-plastic contact between bodies occurs at several points simultaneously. The contact between wires or between the wires and the suspension clamp, which is regarded as a critical location, changes the mechanical properties of the conductor with the emergence and development of contact indents. In order to understand the development of the indents ant their influence in the properties of the wires, indentation, tensile and fatigue tests were performed on wires taken from a steel-aluminium conductor. The problem of normal contact when plastic deformations are much higher than the elastic ones is extremely complex. The convex profile of the wires brings additional complications. Specific strain intensity is proportional to the depth of penetration. Experimental researches have shown that the shape and size of the indents occurred at the contact points have a significant influence on the tensile strength and lifetime of the conductors and local deformations determine certain features of fatigue crack initiation and propagation.