D.E. Manolakos

Crashworthy capability of composite material structures

Abstract Considerable research interest has been directed towards the use of composite materials for crashworthiness applications, because they can be designed to provide impact energy absorption capabilities which are superior to those of metals when compared on a weight basis. This review draws together information from a variety of sources to compare the findings of researchers in this field. The anisotropy of composite materials means that there are a great number of variables controlling mechanical behaviour and much of the investigative experimental work conducted in this area has concentrated on composite tubular specimens. The material, geometrical and experimental factors which have been shown to affect the energy absorption capability of such samples are related and a comparison is made of some of the specific energy absorption values which have been quoted in the literature. A selection of methods for predicting composite material energy absorption capability is presented and consideration is given to some of the more practical aspects of employing composite materials for crashworthiness purposes.

Crashworthy characteristics of axially statically compressed thin-walled square CFRP composite tubes: experimental

In this paper the results of experimental works pertaining to the crash behaviour, collapse modes and crashworthiness characteristics of carbon fibre reinforced plastic (CFRP) tubes that were subjected to static axial compressive loading are presented in detail. The tested specimens were featured by a material combination of carbon fibres in the form of reinforcing woven fabric in thermosetting epoxy resin, and they were cut at various lengths from three CFRP tubes of the same square cross-section but different thickness, laminate stacking sequence and fibre volume content. CFRP tubes were compressed in a hydraulic press of 1000 kN loading capacity at very low-strain rate typical for static testing. The influence of the most important specimen geometric features such as the tube axial length, aspect ratio and wall thickness on the compressive response and collapse modes of the tested tubes is thoroughly analysed. In addition, the effect of the laminate material properties such as the fibre volume content and stacking sequence on the energy absorbing capability of the thin-wall tubes is also examined. Particular attention is paid on the analysis of the mechanics of the tube axial collapse modes from macroscopic and microscopic point of view, emphasizing on the mechanisms related to the crash energy absorption during the compression of the composite tubes.

Finite element simulation of chip formation in orthogonal metal cutting

Abstract A coupled thermo-mechanical model of plane-strain orthogonal metal cutting with continuous chip formation is presented using the commercial implicit finite element code MARC. The flow stress of the work-material is taken as a function of strain, strain-rate and temperature in order to take into account the effect of the large strain, strain-rate and temperature associated with cutting on the material properties. The cutting process is simulated from the initial to the steady-state of cutting force, by incrementally advancing the cutting tool, while a geometrical chip-separation criterion, based on a critical distance at the tool tip regime, is implemented into the MARC code by employing the rezoning procedure. The shape of the chip and the stress, strain and strain-rate distributions in the chip and workpiece, as well as the temperature fields in the workpiece, chip and tool, are determined. The calculated cutting forces are compared with published experimental data and found to be in good agreement, validating, therefore, the proposed FE model.

Extensible plastic collapse of thin-wall frusta as energy absorbers

Abstract The crumpling of thin-walled frusta, under axial compression, in the ‘concertina’ mode is studied. The energy expended in bending at the plastic hinges and in stretching the metal between the hinges is minimized for the total decrease in height due to collapse. The thinning of the cross-section due to stretching is neglected. A theoretical model has been developed and numerical results are obtained that show the effect of slenderness, t/ D , and the semi-apical angle of the frusta. Good qualitative agreement in trends is exhibited when comparison with available experimental results is made.

Artificial neural network models for the prediction of surface roughness in electrical discharge machining

In the present paper Artificial Neural Networks (ANNs) models are proposed for the prediction of surface roughness in Electrical Discharge Machining (EDM). For this purpose two well-known programs, namely Matlab® with associated toolboxes, as well as Netlab®, were emplo- yed. Training of the models was performed with data from an extensive series of EDM experiments on steel grades; the proposed models use the pulse current, the pulse duration, and the processed material as input parameters. The reported results indicate that the proposed ANNs models can satisfactorily predict the surface roughness in EDM. Moreover, they can be considered as valuable tools for the process planning for EDMachining.

Finite element simulation of the axial collapse of metallic thin-walled tubes with octagonal cross-section

Abstract The present paper deals with the implementation of the explicit FE Code LS-DYNA to simulate the crash behaviour and energy absorption characteristics of steel thin-walled tubes of octagonal cross-section subjected to axial loading. The collapse procedure is successfully simulated and the obtained numerical results are compared with actual experimental data from small-scale models and useful concluding remarks pertaining to the design requirements of the crushing process are drawn.

The static and dynamic axial crumbling of thin-walled fibreglass composite square tubes

In the present paper we report on the behaviour and crashworthiness characteristics of square composite tubes subjected to static and dynamic axial compression exerted by a hydraulic press and a drop-hammer, respectively. The effect of specimen geometry, i.e. of thickness and axial length, and of the loading rate on the energy absorbing capability are studied in detail. Attention is directed towards the mechanics of the axial crumbling process from macroscopic and microscopic point of view for facilitating engineering design calculations of the amount of energy dissipated and for a somewhat more complete aspect on the actual fracture mechanism during the failure of the composite material tested. A theoretical analysis of the collapse mechanism of the components tested under axial compression is proposed, leading to a good approximation of the energy absorbed during crushing.

On the inextensional axial collapse of thin PVC conical shells

Abstract Inextensional collapse mechanisms are presented for the axial crumpling of thin-walled circular cones and frusta (truncated circular cones). Shortening of the (thin) shell height is achieved by folding in a non-symmetric diamond mode about stationary circumferential and inclined plastic hinges; collapse proceeds progressively from the narrower end of the conical shell during the passage of a travelling hinge. Expressions for the various mean crushing loads, when collapsing frusta of rigid-perfectly-plastic material, are developed. Theoretical collapse modes and predicted loads are compared with those obtained experimentally by collapsing rigid PVC conical shells of constant axial length, of various wall-thicknesses and semi-apical angles, as well as metal (aluminium alloy and low-carbon steel) conical shells of similar geometry; agreement is found to be good.

Analysis of failure mechanisms observed in axial collapse of thin-walled circular fibreglass composite tubes

Theoretical analysis of the failure mechanism of the stable mode of collapse of thin-walled fibreglass composite tubes under static axial compression, based on experimental observations and taking into account all possible energy absorbing mechanisms developed during the process, is reported. Crushing loads and the energy absorbed are theoretically predicted. The proposed theoretical model was experimentally verified for various composite materials and tube geometries and proved to be very efficient for theoretically predicting the energy absorbing capacity of the shell.

The static and dynamic axial collapse of fibreglass composite automotive frame rails

Abstract An automotive frame rail of hourglass cross-section, made of a glass fibre/ vinylester composite, was designed for use in the apron construction of the car in order to obtain a high degree of crashworthiness at this location of the car body. The crashworthy behaviour of this structural component in axial compression at various strain rates (head-on collision) was studied experimentally. The modes of collapse at macroscopic scale, the microscopic fracture patterns and the energy absorbing capability of such rail beams were examined and discussed. A theoretical analysis of the collapse mechanism of the components tested under axial compression is proposed leading to a good approximation of the energy absorbed during crushing.