Key Engineering Materials Vols. 462-463

Abstract: Structural response of pin-supported metallic foam core sandwich beam is theoretically investigated. Effects of local denting and core strength and interaction of bending and axial stretching are considered in analysis. A rigid-plastic beam-on-foundation is employed to consider local denting deformation. The local denting continues during the overall deformation of sandwich beam. It is shown that upon neglecting the effect of local denting, the load-carrying capacity and energy absorption of sandwich beam may be overestimated, and the normal axial (membrane) force associated with plastic stretching substantially stiffens the sandwich beams.

Abstract: This paper discusses the effect of Al2O3-13% TiO2 agglomerated nanoparticle powders ranging from 20 to 60 m and microparticle powders ranging from 10 to 25 m on commercial marine grade mild steels using a plasma spray technique. Prior to coating, the nanoparticle powders were subjected to a 2 level factorial design of experiment to give a careful control and optimise the operational spray parameters as well as process by using the statistical methods. The method was focused on the primary gas pressure, carrier gas pressure and powder feed rate of the spray parameters. The optimum properties of wear rate, surface roughness and microhardness were identified by using the lowest primary and carrier gas pressure together with the highest powder feed rate. As for the microparticle powders, they were subjected to an optimum properties by using 35 kW plasma spray power. In this study, the plasma spray power for microparticle varied from 20 kW to 40 kW, while the other parameters such as primary gas pressure, carrier gas pressure, powder feed rate and spray distance were held constant. It was found that microparticle powders exhibited denser coating microstructure s and improved both surface roughness and microhardness. On the other hand, the nanoparticle powder coating gave a greater wear resistance than those of micro particle powders, which may likely due to the strengthening effect of both fully and partially melted region.

Abstract: An elastic-plastic finite element analysis (FEA) is used to determine the J-integral around the crack front of 3-dimensional semi-elliptical surface crack in a round bar under torsion loading. Crack geometries are based on the experimental observation. The present model is validated using the SIF under bending loading since no suitable SIF for torsion is available. Lack of numerical solution of elastic and plastic stress parameters under torsion are found. The FE J values are normalized by dividing with the estimation J value using a reference stress method. It is found that higher J values are obtained for deep cracks and the maximum J changed from the deepest point along the crack front to the outer point at the free surface when a/D > 0.2. J values can be estimated for all type of crack geometries under consideration with a correction factor, h1.

Abstract: Fatigue in materials is caused by repeated loading and unloading cycles below the ultimate strength of a material. Fatigue tests are expensive since they required a lot of time consuming. Simulation of fatigue crack propagation using commercial software can reduce the costs related to time. The purpose of this study is to compare the fatigue crack propagation in metal under variable and constant amplitude loading. A standard size of aluminum cast alloy specimen according to ASTM E647 document was modelled using a pre-processor and it was later being analysed. In another aspect, strain gauges were attached to an engine mounting bracket and connected to the data acquisition set in order to capture the actual strain signals when an automobile was driven on to different road conditions. For the simulation purpose, a constant amplitude loading was then derived from a variable amplitude loading obtained from the data capturing process. The related parameters on between different road conditions, variable and constant amplitude loadings and crack propagation rate were presented. The relationship between those parameters were finally correlated and discussed.

Abstract: This paper explores the initial potential of theory of critical distance (TCD) which offers essential fatigue failure prediction in engineering components. The intention is to find the most appropriate TCD approach for a case of multiple stress concentration features in future research. The TCD is based on critical distance from notch root and represents the extension of linear elastic fracture mechanics (LEFM) principles. The approach is allowing possibilities for fatigue limit prediction based on localized stress concentration, which are characterized by high stress gradients. Using the finite element analysis (FEA) results and some data from literature, TCD applications is illustrated by a case study on engineering components in different geometrical notch radius. Further applications of TCD to various kinds of engineering problems are discussed.

Abstract: Based on an exact geometric nonlinear theory for plane curved beams, geometrically nonlinear equilibrium equations and boundary conditions governing the nonlinear bending of a simple plane frame structure subjected distributed loads were derived. By using the shooting method to numerically solve the boundary value problem of nonlinear ordinary differential equations, large deformation equilibrium configurations of a simple frame with both straight and the curved beam elements subjected uniformly distributed load were obtained. The theory and methodology presented can be used to analyze large deformation of plane simple frames with a variety of geometries and loadings.

Abstract: We consider the Saint-Venant torsion problem of composite shafts. Two different kinds of imperfect interfaces are considered. One models a thin interphase of low shear modulus and the other models a thin interphase of high shear modulus. The imperfect interfaces are characterized by parameters given in terms of the thickness and shear modulus of the interphases. Using variational principles, we derive rigorous bounds for the torsional rigidity of composite shafts with cross-sections of arbitrary shapes. The analysis is based on the construction of admissible fields in the inclusions and in the matrix. We obtain the general expression for the bounds and demonstrate the results with some particular examples. Specifically, circular, elliptical and trianglar shafts are considered to exemplify the derived bounds. We incorporate the cross-section shape factor into the bounds and show how the position and size of the inclusion influence the bounds. Under specific conditions, the lower and upper bounds will coincide and agree with the exact torsional rigidity.

Abstract: Concrete is a three-phase material consisting of cement paste matrix, discrete inclusions of sand (aggregate), and an interfacial transition zone (ITZ) between the matrix and the inclusions. In order to calculate the elastic properties of the ITZ of cement mortar, We model the material as a composite formed by a matrix with embedded spherical particles; each surrounded by a concentric spherical shell. With help of the generalized self-consistent method (GSCM), equations of bulk modulus and shear modulus of ITZ are deduced, and Elastic properties of ITZ are computed by using experimentally known elastic properties of the composite. It is found that the shear modulus of ITZ is about 50% of that of the cement paste matrix.

Abstract: This paper presents a data fusion technique to model more certain probabilistic full-field strain/displacement measurements for stochastic energy-based characterization proposed by the authors. The proposed technique measures the full-field measurements by using multiple cameras, constructing a Gaussian probability density function (PDF) for each camera, fusing the PDFs and developing the total PDF of the full-field measurements. Since the certainty of measurements is magnified by the use of multiple cameras, the use of multiple well-calibrated cameras could achieve the accuracy which no single camera could attain. The validity of the proposed energy-based characterization and its superiority to the original formulation were investigated using numerical analysis of an anisotropic material, and the proposed technique was found to improve the accuracy significantly with the addition of cameras.

Abstract: This paper discusses the effect of several variables in plasma spray method, namely; the flow rate, spray distance and power used on the mechanical properties of Cu-Ni coated A7075. All spraying techniques were designed using 23 factorial plans prior to the actual experiments. The produced coatings were characterised using a scanning electron microscopy (SEM). Morphological observation indicated that most sprayed particles were formed in splash shape splats. The effects of interactions between the response variable factors were screened using a response surface methodology. Three coating factors were used, namely, plasma power, number of coating layer and spraying distance where as the coating hardness and surface roughness were set as the responses. In general, an ideal parameter of 5 coating layers with a power of 30 kW and a spraying distance of 150 mm gave a maximum hardness of 622 Hv and a minimum surface roughness of 9.7 µm.