Monir Takla

Evaluation of thermal and evaporative resistances in cricket helmets using a sweating manikin.

The main objective of this study is to establish an approach for measuring the dry and evaporative heat dissipation cricket helmets. A range of cricket helmets has been tested using a sweating manikin within a controlled climatic chamber. The thermal manikin experiments were conducted in two stages, namely the (i) dry test and (ii) wet test. The ambient air temperature for the dry tests was controlled to ~ 23 °C, and the mean skin temperatures averaged ~ 35 °C. The thermal insulation value measured for the manikin with helmet ensemble ranged from 1.0 to 1.2 clo. The results showed that among the five cricket helmets, the Masuri helmet offered slightly more thermal insulation while the Elite helmet offered the least. However, under the dry laboratory conditions and with minimal air movement (air velocity = 0.08 ± 0.01 ms(-1)), small differences exist between the thermal resistance values for the tested helmets. The wet tests were conducted in an isothermal condition, with an ambient and skin mean temperatures averaged ~ 35 °C, the evaporative resistance, Ret, varied between 36 and 60 m(2) Pa W(-1). These large variations in evaporative heat dissipation values are due to the presence of a thick layer of comfort lining in certain helmet designs. This finding suggests that the type and design of padding may influence the rate of evaporative heat dissipation from the head and face; hence the type of material and thickness of the padding is critical for the effectiveness of evaporative heat loss and comfort of the wearer. Issues for further investigations in field trials are discussed.

A collaborative FEA platform for rapid design of lightweight vehicle structures

This paper presents a novel methodology for rapid design of sustainable vehicle structures using a collaborative Finite Element Analysis (FEA) platform. The developed platform utilises FEA substructures in a novel way to increase the vehicle development efficiency by speeding up analysis and reducing the number of iterations in the product development process. It also allows rapid validation of design changes early in a design and therefore reduction of computational effort and time without compromising accuracy. The underpinning methodology was described and illustrated here using a case study dealing with the design and optimisation of a car seat actuator assembly.

Design Optimisation of Passenger Car Hood Panels for Improved Pedestrian Protection

This article presents research motivated by the prospect of imminent implementation of the new regulatory requirement for pedestrian protection GTR9 (Global Technical Regulation9). A new methodology has been developed for optimisation of the hood panel of passenger cars to ensure that the pedestrian Head Injury Criterion (HIC) falls below the threshold values specified by both the GTR9 and the consumer metric, the Australian New Car Assessment Program (ANCAP). To meet the performance criteria for pedestrian protection head impact, it is vital to incorporate the associated design parameters into the hood design process at an early stage. These parameters are architectural in nature whereby changing them later in the vehicle design process would be very expensive and difficult to implement. The developed methodology for the design of a hood configuration aims to provide a robust and homogeneous HIC for different impact positions in the central area of the hood of a large sedan, taking into consideration the limited space available for deformation. The non-linear Finite Element Analysis (FEA) software LS-DYNA was used in this research to simulate the GTR-9/ANCAP pedestrian head impact testing procedures. The efficiency of a hood design was calculated as the ratio of the theoretical optimal deformation of hood assembly for a given value of HIC to the actual deformation calculated for the same HIC value of the corresponding numerical test. The efficiency and HIC value were derived for each configuration and compared to obtain the optimal solution for homogeneous performance and minimal deformation of outer and inner hood panels. The Kriging response surface and the Monte Carlo method were used in the design of numerical experiments. The outcomes of this study provide a clear indication that an optimum configuration of the hood panel of a passenger car can be developed to minimize the hood deformation while meeting the requirement for HIC value.

Theoretical and Numerical Investigation of the Elastic-Plastic Behavior of Thick-Walled Cylinders

This chapter presents a theoretical and numerical investigation of the elastic-plastic behavior of thick-walled cylindrical pressure vessels loaded by combined large hydrostatic pressure and axial force. A novel approach is introduced for developing general theory, considering material behavior with nonlinear isotropic hardening. The adopted constitutive law is based on applying the von Mises yield criterion in association with the normality rule. The resulting stress and strain distributions are obtained and presented for a case study of combined internal pressure and axial load. The theoretical analysis is validated by comparing the results with those obtained numerically using nonlinear finite element simulation. This investigation addresses a persisting unresolved problem and provides a solution which results in continuous stress and strain fields throughout the cylinder wall. Earlier attempts cited in literature provided incorrect solutions due to invalid assumptions and/or inadequate selection of the yield criterion. The findings provide valuable information in the safety design of extremely loaded pressure vessels and establish the basis for further research in this field.

Comparative Evaluation of Engineering Design Concepts Based on Non-Linear Substructuring Analysis

The paper presents a novel approach to comparative evaluation of engineering design concepts that exhibit non-linear structural behaviour under load. The developed method has extended the substructures technique in order to apply the Finite Element Analysis (FEA) method to complex non-linear structural problems in the conceptual design phase. As conventional FE models based on substructures allow only linear analysis, it was necessary in this research to introduce a new algorithm capable of linearizing non-linear structural problems with sufficient accuracy in order to enable comparative evaluation of design concepts relative to each other under the given constraints and loading conditions. A comparative study with respect to model size, efficiency, accuracy and confidence was performed to validate the developed method. Obtained results indicate significant improvement over more traditional approaches to applying FEA in the conceptual design phase. The improvements achieved using the developed method compared to the traditional FE based approach are superior by a factor of 2.7 in efficiency and by a factor of 4.5 in confidence while not sacrificing the optimality of the solutions.

AN EXTENDED SUBSTRUCTURING TECHNIQUE FOR EFFICIENT EVALUATION OF NONLINEAR LOAD-BEARING STRUCTURES IN THE CONCEPTUAL DESIGN STAGE

The research presented in this paper has extended the substructuring technique into the nonlinear domain in order to apply the finite element analysis (FEA) method to complex nonlinear structural design problems in the conceptual design stage. As conventional FE models based on substructures allow only linear analysis, it was necessary in this research to introduce a new algorithm capable of linearizing nonlinear structural problems with sufficient accuracy in order to enable evaluation of engineering design concepts in a more objective and rigorous manner in the early stages of design. The developed method was implemented within a commercial FE solver, and validated using a select number of case studies. The results obtained for the two sample solutions indicate that the new method has achieved an improvement in accuracy of 90% and 98% respectively compared to the conventional FE-based approach applied to the same class of design problems.

Biomimetic Design of Lightweight Vehicle Structures Based on Animal Bone Properties

This paper presents a comprehensive biomimetic design approach to developing novel load bearing lightweight vehicle structures inspired by the structural properties of animal bones. Lightweight vehicle structures developed in this way would have increased stiffness at significantly reduced weight. In this research, trabecular (cancellous) bone was analyzed at the metaphyses of four different species including rat, rabbit, chicken, and sheep. Three-dimensional models of bone structures were reconstructed from micro-CT scanned images using the computer aided design software Mimics. Force resistance and energy absorption properties of relevant bone structures subjected to quasi-static compression loads were investigated and analysed using the Finite Element (FE) method. Based on the obtained results, the paper discusses the effects of load directions, bone structure allocation and model thickness on the energy absorption and force resistance of the bone structures. The simulation results obtained in this research were compared to the results of conventional vehicle side intrusion bars.

Development of Simplified Spot Weld Models: Stiffness Prediction and Computational Performance Evaluation

Simple spot weld connection models are desirable in huge and complicated finite element models of automotive body-in-white structures which generally contains thousands of spot weld joints. Hence, in this paper six different individual spot weld joint finite element models simplified in terms of their geometric and constitutive representations were developed including the one that is currently used in automotive industries. The stiffness characteristics of these developed models were compared with the experimental results obtained following a simple strategy to design the welded joint based on the desired mode of nugget pull out failure. It was found that the current spot weld modeling practice in automotive industry under predict the maximum joint strength nearly by 50% for different loading conditions. The computational costs incurred by the developed models in different loading conditions were also compared. Hence, a suitable model for spot welded joints is established which is very simple to develop but relatively cheap in terms of computational costs.© 2010 ASME

Enhanced non-linear material modelling for analysis and qualification of rollover protective structures

Finite element simulations of a rollover protective structure are an important aspect in its design, as it provides a means of structural integrity qualification prior to the required destructive testing. A good understanding of the rollover protective structure behaviour under simulated loading offers engineering practitioners the opportunity to optimize the design. The testing conditions, which are outlined in the applicable standards, result in plastic deformation of the rollover protective structure, associated with material hardening of various areas of the structure. An accurate description of the material behaviour is important for finite element simulations of the structural response. This research examines some of the hardening models commonly used in simulations of rollover protective structures, which are available in most finite element commercial software, including linear and multi-linear isotropic and kinematic hardening models and non-linear kinematic hardening models. The numerical performance of the plasticity models in representing the material behaviour was compared with the experimental data for commonly used rollover protective structure material. Analysis revealed the potential benefits and drawbacks of the various models. Moreover, a damage-induced softening model was implemented at the structure joints in conjunction with the non-linear hardening models. Enhanced computational results were obtained through this modelling variation, highlighting the importance of material modelling at the primary structure and the joints of a rollover protective structure.

Optimization of Hood Design to Minimise Pedestrian Head Injury in Impact

The main objective of this work was to develop a methodology for optimising the hood assembly for minimal deformation with robust and homogeneous impact behaviour in a pedestrian head impact. In practice, the design of the outer and inner hood panels must meet all general design requirements in addition to pedestrian head impact performance.