Showing papers by "Ignaas Verpoest published in 2007"

Biomechanics of frontal skull fracture

Abstract: The main purpose of the present study was to investigate whether an energy failure level would apply to the skull fracture mechanics in unembalmed post mortem human heads under dynamic frontal loading conditions. A double-pendulum set-up was used to conduct frontal impact tests on specimens from eight unembalmed post mortem human subjects. The specimens were isolated at the occipital condyle level and pre-test computed tomography images were obtained. The specimens were rigidly attached to an aluminum pendulum in an upside down position and obtained a single degree of freedom, allowing motion in the plane of impact. A steel pendulum delivered the impact and was fitted with a flat-surfaced, cylindrical aluminum impactor, which distributed the load to a force sensor. The relative displacement between the two pendulums was measured using a laser sensor and used as a measure for the deformation of the specimen in the plane of impact. Two impact velocity conditions were created: low (3.60±0.24 m/s) or high (5.18±0.04m/s) velocity. Computed tomography and dissection techniques were used to detect pathology. If no fracture was detected, repeated tests on the same specimen were performed with higher impact energy until fracture occurred. Eventually all specimens were fractured. Peak force, displacement and energy variables were used to describe the biomechanics. These preliminary data suggest a positive correlation between impact velocity and energy to fracture. Further experiments are necessary to elucidate the possibility of an energy criterion for skull fracture in head impacts.

Mechanical Behaviours for Textile Composites by FEM Based on Damage Mechanics

Abstract: To make an expansion of composite consumption ever widening with use at demanding and safety critical applications, it is important to establish the evaluation technique of the strength, the safety, etc. To reach the goal with a useful reliable technique, we have developed a numerical simulation program on damage development of composites based on damage mechanics. The following points are the keys to simulate the mechanical behavior; (1) The generation technique of FE model with yarns and matrix, (2) The classification of anisotropic damage mode based on damage mechanics, (3) Multi-scale modeling by Mesh superposition method. In this paper, the numerical technique and the results of multi-scale analysis of woven composites are described.

Strain mapping analysis of various textile composite and noise filtering of the data

Abstract: The focus of the work is meso scale analysis (scale level of the fabric unit cell) of textile composite deformation and failure. The following structures have been studied: brittle carbon epoxy composites (triaxial braided and quasi unidirectional composites), and thermoplastic glass woven structure (twintex). Since the unit cell of these composite is quite large (4-14 mm) the surface strain measurement gives a sound base for meso strain distribution study. The latter serves twofold: (1) experimental investigation, which includes study of strain distribution at various stages of deformation, plasticity detection, damage initiation; (2) numerical investigation, which aimed at verification of the correspondent finite element models. In carbon-epoxy composites non-elastic deformations at early stages (about 0.3 % of applied deformation) relate to transverse crack occurrence in fibre bundles. Damage in carbon-epoxy composite starts early and that’s why it is crucial to analyse strain distribution when studied signal is comparable with a measurements noise. Based on assumption of linear elastic behaviour a regression of local strain versus applied strain was proposed. It allows filtering the noise without loosing in resolution of the signal. Based on the statistics of the strain fields an on-set and location of the damage was detected. The latter was supported by acoustic emission measurements. Strong plastic deformation is the case of the thermoplastic composite. Similar strategy was proposed for filtering of the fields obtained for the thermoplastic composite. On the contrast with the carbon-epoxy composites the local strain regression here is of higher orders. The filtered strain showed a good correspondence with the finite element analysis of the composite at the meso (unit cell) level.

Development and Validation of a Continuous Production Concept for Thermoplastic Honeycomb

Abstract: The continuous production of thermoplastic honeycomb cores is a recent development at K.U.Leuven. The production equipment has been improved to deliver high quality material. This equipment is used for the determination of optimum process parameters. This paper describes the production equipment, its development and the experiments that have been done.