Hervé Morvan

Determination of pre-impact occupant postures and analysis of consequences on injury outcome. Part I: A driving simulator study

This paper considers pre-impact vehicle maneuvers and analyzes the resulting driver motion from their comfort seating position. Part I of this work consists of analyzing the driver behavior during a crash. The study is conducted using the LAMIH driving simulator and involves 76 participants. The emergency situation is created by a truck emerging from behind a tractor on the opposite side of the road and tearing along the participant. The driver positioning throughout the simulation is recorded via five video cameras allowing view of the front scene, the driver face, feet and pedals, hands on the steering wheel and global lateral view. Data related to braking force, seat pressure, muscular activity for major groups of muscles and actions on the steering wheel are also collected. The typical response to this type of emergency event is to brace rearward into the seat and to straighten the arms against the steering wheel, or, to swerve to attempt to avoid the impacting vehicle. While turning the steering wheel, the forearm can be directly positioned on the airbag module at time of crash which represents a potential injurious situation. These positions are used in Part II to determine scenario of positions for numerical simulation of a frontal collision.

Experimental Investigation and Modeling of Driver's Frontal Pre-crash Postural Anticipation

This paper presents the first experiment managed within the framework of the regional French project ST2 (French acronym for Sciences and Technologies for Safety in Transports). This program aims to study human pre-crash behavior in order to improve the efficiency of passive safety protection systems. An experiment was carried out using a driving simulator of LAMIH for hvestigating drivers frontal pre-crash postural changes. A scenario of an unavoidable crash was designed. To increase the level of realism during the crash, a real impact was added between the windscreen and a foam rubber block in addition to a truck horn sound. Risk car driver postures just before a frontal crash have been determined The results have shown that none of the subjects adopted the standardized driving position during the collision and 30% of the subjects adopted a position with the left hand placed in front of steering wheel which can be considered as a risk position. This is confirmed by a simulation using Madymo. In order to develop a pre-crash driving postural prediction model, a methodology of quantifying pre-crash postures has been proposed using a digital model developed by INRETS.

A three-dimensional geometric quantification of human cortical canals using an innovative method with micro-computed tomographic data

The complex architecture of bone has been investigated for several decades. Some pioneer works proved an existing link between microstructure and external mechanical loading applied on bone. Due to sinuous network of canals and limitations of experimental acquisition technique, there has been little quantitative analysis of three-dimensional description of cortical network. The aim of this study is to provide an algorithmic process, using Python 3.5, in order to identify 3D geometrical characteristics of voids considered as canals. This script is based on micro-computed tomographic slices of two bone samples harvested from the humerus and femur of male cadaveric subject. Slice images are obtained from 2.94 μm isotropic resolution. This study provides a generic method of image processing which considers beam hardening artefact so as to avoid heuristic choice of global threshold value. The novelty of this work is the quantification of numerous three-dimensional canals features, such as orientation or canal length, but also connectivity features, such as opening angle, and the accurate definition of canals as voids which ranges from connectivity to possibly another intersection. The script was applied to one humeral and one femoral samples in order to analyse the difference in architecture between bearing and non-bearing cortical bones. This preliminary study reveals that the femoral specimen is more porous than the humeral one whereas the canal network is denser and more connected.

Experimental protocol to characterise damage of appendicular bone

Appendicular bone looks like composite material with long fibres and a matrix; the fibres are replaced by porous Haversian canals in the longitudinal direction and Volkmann canals in the transverse direction (Figure 1 (a)). Due to its architecture, orthotropic behaviour model with transverse isotropy can be used (Bry et al. 2012). The porosity introduced by the Haversian andVolkmann canals leads to the identification of apparent behaviour and consequently non-accurate mechanical properties (stiffness and resistance) when performing classical mechanical tests. To identify the true mechanical properties of appendicular bone, the porosity and its evolution during loading have to be modelled and measured (Xiang-Dong et al. 1994). The continuum damagemodel is a good candidate to compute the effective stress and the damage evolution. The damage is defined by a second-order tensor in the orthotropic frame and canbe identified easily by using tensile tests (Lemaitre 1992). To identify the mechanical behaviour of this damaged material, an experimental protocol has been developed. A ‘normalised’ shape closer as possible as a parallelepiped form is done to the samples harvested from appendicular bone in longitudinal and transverse directions. The initial porosity is measured in longitudinal and transverse directions by using X-ray microtomography (Figure 1(a)). To avoid intra-variability, tensile and compressive cyclic tests are done at first to identify the stiffness (elasticity modulus and Poisson’s ratio) and followed by loading/unloading tests, without taking down the specimen, carriedout until rupture to compute thedamage evolution by measuring the elasticity modulus degradation. This experimental protocol is used to characterise the behaviour until the rupture of male PMHS humeri.

Exploration of human behaviour during pre-crash phase: Modeling and consequences during the collision

In order to quantify the efficiency of passive security systems on injury severity, European normalized crash tests (Directive 1999/98/CE) are performed with a 50th percentile dummy. Then, injury level is approximated using specific criteria related to critical body segments like the HIC (Head Injury Criterion). Precise rules are imposed by the European norm to position the dummy, whose posture must represent a seated and restrained driver. Particularly, hands are on the steering wheel and the superior part of the torso leans back in the seat. Thus, passive systems efficiency doesn’t take into account the drivers anthropometry, real comfort driving position (Hetier et al. 2002), and reflex reactions facing with an incident (Hetier et al. 2004).