Kamran Behdinan

Numerical simulation of normal and oblique ballistic impact on ceramic composite armours

This paper presents three-dimensional finite element models that investigate the performance of ceramic–composite armours when subjected to normal and oblique impacts by 7.62 AP rounds. The finite element results are compared with experimental data from different sources both for normal and oblique impact, respectively. Simulation of the penetration processes as well as the evaluation of energy and stresses distributions within the impact zones highlight the difference between normal and oblique ballistic impact phenomena. The findings show that the distributions of global kinetic, internal and total energy versus time are similar for normal and oblique impact. However, the interlaminar stresses at the ceramic–composite interface and the forces at the projectile– ceramic interface for oblique impact are found to be smaller than those for normal impact. Finally, it is observed that the projectile erosion in oblique impact is slightly greater than that in normal impact. 2003 Published by Elsevier Ltd.

Multidisciplinary optimization framework for control-configuration integration in aircraft conceptual design

The emerging flight-by-wire and flight-by-light technologies increase the possibility of enabling and improving aircraft design with excellent handling qualities and performance across the flight envelope. As a result, it is desired to take into account the dynamic characteristics and automatic control capabilities at the early conceptual stage. In this paper, an integrated control-configured aircraft design sizing framework is presented. It makes use of multidisciplinary design optimization to overcome the challenges which the flight dynamics and control integration present when included with the traditional disciplines in an aircraft sizing process. A commercial aircraft design example demonstrates the capability of the proposed methodology. The approach brings higher freedom in design, leading to aircraft that exploit the benefits of control configuration. It also helps to reduce time and cost in the engineering development cycle.

Applicability and viability of a GA based finite element analysis architecture for structural design optimization

Abstract A genetic algorithm (GA) based finite element analysis (FEA) procedure was developed for size and shape optimization of planar and space trusses. The purposed procedure interfaces a binary GA within a FEA software package in order to initially test the applicability and viability of such integration. In addition, special features of the GA were included to dynamically alter the population size, and the crossover and mutation rate in order to facilitate faster convergence and hence reduce the computational effort required. In other words, the GA adapted itself as search and optimization process progressed. The paper also brings a focus on the applicability of integrating a GA as an optimization tool within a FEA software. It was shown by way of many examples––solved by numerous mathematical, as well as other heuristic approaches in the literature––that the purposed methodology is quite efficient and capable of finding lighter and reasonable structural designs than that reported in the literature. Moreover, it is shown that the purposed method removes the immense effort required in coding ones own finite element codes by utilizing already existing finite element software. Nonetheless, it was found that even with a GA, optimization for very large problems was computationally extensive.

A material and gauge thickness sensitivity analysis on the NVH and crashworthiness of automotive instrument panel support

Abstract This paper provides a finite element analysis of the effects of using alternative materials and gauge thickness on the weight and structural performance of the VN127 instrument panel support. Two types of analyses were performed, NVH and crashworthiness. The NVH analysis was used to determine the structure’s natural frequencies, whereas the crashworthiness analysis was used to examine the structure’s crash behavior under two different impact conditions. The materials used in this study included mild steel, aluminum and magnesium alloys. The thickness of the structure was varied from 0% to 40%, in increments of 10%. The results of different models were compared with the baseline model, i.e., the mild steel model with nominal thickness. It was found that by replacing mild steel with aluminum alloys, and increasing the gauge thickness of the structure by 40%, the NVH and crashworthiness performance of the structure was equivalent to the baseline model.

In vitro technique in estimation of passive mechanical properties of bovine heart: Part I. Experimental techniques and data

Myocardium generally demonstrates viscoelastic behavior. Since the stress-stain relationships of tissues are pseudo-elastic, their mechanical behavior can be defined as hyperelastic. In this work, mechanical properties of bovine heart were studied. In this study, the experimental technique for testing myocardium is explained and the experimental data are presented. First, the heart was perfused and the specimens were cut from different regions of the heart. Second, the materials preferred direction was identified. Then, a series of uniaxial, biaxial and equibiaxial test were performed on specimens taken from: left ventricle free wall (LVFW), right ventricle free wall (RVFW), left ventricle mid-wall (LVMW) and apex. Test specimens were preconditioned by applying cyclic load to reduce the viscoelastic effect. After preconditioning, the samples were tested at various stretch rates and loading conditions. Finally, a conclusion is made on the experimental data.

Prediction of Bearing Strength in Fiber Metal Laminates

Finite element (FE) analyses are carried out on bolt bearing testing scenarios based on data found in the literature. Both layer-by-layer and smeared property FE models are created to calculate the compressive characteristic dimension (CCD) for three GLARE variants. A novel re-definition of conventional CCD is proposed which is governed by the yield strength of aluminum. The new definition also incorporates the two-phase nature of GLARE, as well as the delamination/ buckling phenomenon for pin/bolt bearing, in a bearing failure mode. A previously unconsidered, orthotropic plate buckling analysis is also conducted in a conservative, worst case scenario sense on the laterally unsupported prepreg layers. Results of the buckling analysis suggest that the prepreg contribution to bearing strength, in a bearing failure mode, is at best negligible and joint collapse is governed by the yielding and delamination of the aluminum layers. Calculation of a CCD, based on the new yield strength definition, produced consistent values amongst all GLARE variants considered in the layer-by-layer analysis suggesting that the CCD is a property of the material alone.

In vitro technique in estimation of passive mechanical properties of bovine heart part II. Constitutive relation and finite element analysis

A pseudo-elastic constitutive equation describing the mechanical properties of bovine myocardium was developed. The myocardium was modeled as a hyperelastic transversely isotropic material with a minimum viscoelastic loses. The material parameters for the proposed constitutive equations were determined using GA regression technique. In this work, the development of a constitutive equation based on principal stretch ratios is explained. The predictive capability of proposed model was compared against the experimental data obtained from part one. Finally, the constitutive equations were implemented into a commercial finite element program and the results of the mathematical model and FEM were compared with the experimental data.

Dynamic Modeling and Simulation of Percussive Impact Riveting for Robotic Automation

Dynamic modeling and simulation of percussive impact riveting are presented for robotic automation. This is an impact induced process to deform rivets, which involves an impact rivet gun driven under pneumatic pressure to pound a rivet against a bucking bar. To model this process, first, a new approach is developed to determine the hammer output speed under input pneumatic pressure. Second, impact dynamics is applied to model the impact acting on the rivet under the hammer hits. Finally, elastoplastic analysis is carried out to derive nonlinear equations for the determination of permanent (plastic) deformations of the rivet when hitting the bucking bar. For simulation, numerical integration algorithms are applied to solve the impact dynamic model and determine the riveting time according to riveting specifications. Riveting tests are carried out for model validation. Agreement between the simulation and experimental results shows the effectiveness of the proposed method.

Uncertainty-based MDO for aircraft conceptual design

Purpose – The purpose of this paper is to study the consideration of uncertainty from analysis modules for aircraft conceptual design by implementing uncertainty-based design optimization methods. Reliability-Based Design Optimization (RBDO), Possibility-Based Design Optimization (PBDO) and Robust Design Optimization (RDO) methods were developed to handle uncertainties of design optimization. The RBDO method is found suitable for uncertain parameters when sufficient information is available. On the other hand, the PBDO method is proposed when uncertain parameters have insufficient information. The RDO method can apply to both cases. The RBDO, PBDO and RDO methods were considered with the Multidisciplinary Design Optimization (MDO) method to generate conservative design results when low fidelity analysis tools are used. Design/methodology/approach – Methods combining MDO with RBDO, PBDO and RDO were developed and have been applied to a numerical analysis and an aircraft conceptual design. This research eva...

Decomposition-Based Simultaneous Stabilization with Optimal Control

Simultaneous stabilization addresses the stability of multiple plants under a single feedback controller. It is desired for aircraft flight control operating under different conditions, when they are represented by a collection of linear dynamic models. The single controller brings continuity and a level of reliability. This paper presents a decomposition approach for the solution to the simultaneous stabilization problem. A bilevel design optimization architecture is adopted in which design of each individual plant (flight condition) is taking place at the bottom level, and the top-level optimization aims for single-control convergence of those individual controllers. Furthermore, performance requirements can be taken into account concurrently with the stabilization process, thanks to the separate bilevel decomposition concept. The effectiveness of the proposed approach is illustrated by different aircraft control system design test cases.