The effect of tube dimensions on optimized pressure and force loading paths in tube hydroforming process

The precise control of internal pressure and axial force loading paths significantly affects the final product quality. In this study, the effect of tube dimensions on the pressure and force loading paths in tube hydroforming process is investigated by using simulated annealing optimization method linked to a commercial finite element code. The optimized loading paths, obtained for different tube geometries with a constant expansion ratio, are then compared. The effects of initial diameter and wall thickness on shape conformation, optimal internal pressure and axial force (or feed) are discussed on the basis of optimal loading paths. Several guidelines in prediction and determination of tube hydroforming parameters are obtained by optimization analysis.     

An Inverse Modeling Approach to Calibrate Parameters for a Drainage Model with Two Optimization Algorithms on Homogeneous/Heterogeneous Soil

Water Resources Management - Due to the time and spatial limitations of subsurface drainage pilots, simulation models have been extensively applied for evaluating these systems. Since the accuracy...     

Explosive welding of stainless steel–carbon steel coaxial pipes

Bi-metallic corrosion resistant steel pipes were produced through explosive welding process. The weldability window of the stainless steel pipe (inner pipe) and the carbon steel pipe (outer pipe) was determined by the use of available semi-empirical relations. The impact velocity of the pipes as the most important collision parameter was calculated by the finite element simulation. Direct effect of the explosive mass reduction on the bonding interface of the pipes was studied. Optical microscopy study showed that a transition from a wavy interface to a smooth one occurs with decrease in explosive load.     

Theoretical and experimental studies of the instantaneous folding force of the polyurethane foam-filled square honeycombs

This paper presents a theoretical formula to predict the instantaneous folding force of a polyurethane foam-filled square column as a single unit of square honeycombs under axial loading. For this purpose, sum of the dissipated energy rate under folding deformations of the square column and the dissipated energy rate of polyurethane foam compression was equated to the work rate of the external force on the structure. The dissipated energy rate of compression and deformation of polyurethane foam was obtained by presenting a new deformation model and through the reduced volume ratio. The final formula obtained, reasonably predicts the instantaneous folding force of the polyurethane foam-filled square column. Finally, according to the calculated theoretical relation, the instantaneous folding force of the foam-filled square column was sketched versus the axial displacement and compared to the experimental results, which showed a good correlation.     

A model for ballistic impact on multi-layer fabric targets

An analytical model has been developed in this paper for the ballistic impact behavior of two-dimensional woven fabric composites of interest in body armor applications.     

Analysis of rupture instability in the hydromechanical deep drawing of cylindrical cups

This paper presents analyses of tensile instability in the hydromechanical deep drawing process of cylindrical cups. Analytical models are developed based on Barlat-Lian and Hill’s non-quadratic yield criteria and the maximum permissible fluid pressure, above which rupture occurs, is achieved, assuming plane strain tensile failure. The influences of process and material variables on this critical fluid pressure are investigated. The theoretical results are compared with results obtained from experiments to verify the validity of the proposed analytical approaches.     

Correlation Between Numerical Finite Element Simulation and Experiments for Explosive Cladding of Nickel Base Super Alloy on Hot Tool Steel

Abstract: Experimental tests were carried out to explosively clad solution‐annealed Inconel 718 super alloy on quench‐tempered AISI H13 hot tool steel. The tests were performed using various stand‐off distances and explosive–to‐flyer plate mass ratios. Various interface geometries were obtained from these experiments. All the experiments were simulated using ABAQUS version 6.9 finite element software. The Williamsburg equation of state and Johnson–Cook constitutive equation with its corresponding failure equation were used to model the behaviour of explosive and plates, respectively. The experimental results showed that the shape of interface fell roughly into three classes, wavy or wavy with some vortex shedding or smooth‐wavy. Various interface morphologies were achieved by changing the stand‐off distances and explosive–to‐flyer plate mass ratios because of change of impact velocity and dynamic collision angle. Numerical results showed that high localised plastic deformation was produced at the bond interface. Equivalent plastic strain and shear stress could be criteria for transition of interface morphology. Welding window of alloys was also developed.     

High-velocity impact loading in honeycomb sandwich panels reinforced with polymer foam: a numerical approach study

The employment of lightweight structures is one of the most important goals in various industries. The lightweight sandwich panel is an excellent energy absorber and also a perfect way for decreasing the risk of impact. In this paper, a numerical study of high-velocity impact on honeycomb sandwich panels reinforced with polymer foam was performed. The results of numerical simulation are compared with the experimental findings. The numerical modeling of high-velocity penetration process was carried out using nonlinear explicit finite-element code, LS-DYNA. The aluminum honeycomb structure, unfilled honeycomb sandwich panel, and the sandwich panels filled with three types of polyurethane foam (foam 1: 56.94, foam 2: 108.65, and foam 3: 137.13 kg/m³) were investigated to demonstrate damage modes, ballistic limit velocity, absorbed energy, and specific energy absorption (SEA) capacity. The numerical ballistic limit velocity of sandwich panels, filled with three types of foam, was more than that of a bare honeycomb core and unfilled sandwich panel. In addition, the numerical results showed that the sandwich panel filled with the highest density foam could increase the strength of sandwich panel and the numerical specific energy absorption of this structure was 23% more than that of unfilled. Finally, the numerical results were in good agreement with experimental findings.

     

Early detection of basal stem rot disease (Ganoderma) in oil palms based on hyperspectral reflectance data using pattern recognition algorithms

Basal stem rot (BSR) is a fatal fungal (Ganoderma) disease of oil palm plantations and has a significant impact on the production of palm oil in Malaysia. Because there is no effective treatment to control this disease, early detection of BSR is vital for sustainable disease management. The limitations of visual detection have led to an interest in the development of spectroscopically based detection techniques for rapid diagnosis of this disease. The aim of this work was to develop a procedure for early and accurate detection and differentiation of Ganoderma disease with different severities, based on spectral analysis and statistical models. Reflectance spectroscopy analysis ranging from the visible to near infrared region (325–1075 nm) was applied to analyse oil palm leaf samples of 47 healthy (G0), 55 slightly damaged (G1), 48 moderately damaged (G2), and 40 heavily damaged (G3) trees in order to detect and quantify Ganoderma disease at different levels of severity. Reflectance spectra were pre-processed, and principal component analysis (PCA) was performed on different pre-processed datasets including the raw dataset, first derivative, and second derivative datasets. The classification models: linear and quadratic discrimination analysis, k-nearest neighbour (kNN), and Naïve–Bayes were applied to PC scores for classifying four levels of stress in BSR-infected oil palm trees. The analysis showed that the kNN-based model predicted the disease with a high average overall classification accuracy of 97% with the second derivative dataset. Results confirmed the usefulness and efficiency of the spectrally based classification approach in rapid screening of BSR in oil palm.