The abdomen consists of the relatively soft area of the torso from the bottom of the rib cage to the top of the pelvis girdle having no skeletal protection from either the front or side and partial protection from the spine from the back.
As the major organs, intestines and bladder, are ‘hollow’, they can sustain considerable compression before injury. The injury is normally due to ruptures rather than contusions.
Several injury criteria have been proposed for the abdomen:
These have been reviewed by S.W. Rouhana in Accidental Injury with tables for each of the criteria and possible tolerance levels (Ref. – 2.1 Pages 417 – 420)
Most of these have been applied to either individual mainly ‘solid’ organs, or the upper portion of the abdomen, which has been included in the thorax injury criteria. The most predictive criterion for injury level is Force x Compression which in terms of injury mechanisms correlates well with the viscous criteria for ‘solid’ organs in the thorax. But as the lower abdomen characteristic for both physical tests and computer simulations will be based on a Force / Deflection characteristic then compression would be an as accurate predictor of injury severity.
S.W. Rouhana et al (Ref: 2.1.4 SAE Papers 892440 and 902317) produced a force / deflection characteristic for the lower abdomen. This was part of a research programme for predicting injuries from occupant submarining, causing the lap belt to override the pelvis so directly loading the abdomen. As such this is related to mainly frontal impacts. The characteristic was based on biomechanical tests using a simulated seat belt at impact velocities of 2 – 6 ms-1, which is at the lower range of abdomen to table edge impacts. Further research will be required to improve this characteristic so it can be applied to the rail environment.
In the development of the EuroSID dummy considerable research work was conducted to formulate an abdomen injury criteria for lateral impacts on the occupant. A peak force criteria was defined, based on injuries not just to the intestines but also liver and kidneys, from impacts from flat and relatively soft impactors, and using the measurement technique designed for the dummy. Therefore at present it is probably not applicable to the blunt rigid objects in the rail environment, so it is proposed to use the compression based injury criteria for both frontal and lateral impacts.
The Abdomen Injury Criteria can be applied to all blunt object impacts to the lower abdomen, bottom of the rib cage to top of the pelvis, both in frontal and lateral impacts. The Abdomen Injury Criteria being most accurate in predicting abdomen injuries with straight edged blunt objects such as table edges.
Crash Test dummies and physical simulators – A frangible abdomen, made from ‘Styrofoam’, has been developed for the HIII crash test dummy specifically for investigating the effects of a seat belt overriding the pelvis in motor vehicle accidents. Although it has been applied to predicting abdominal injuries in table edge impacts, its behaviour in direct impacts with rigid blunt objects, is not repeatable, giving non consistent results. New test methods utilising better deforming materials which meet the abdomen force / deflection characteristics, are required before the abdomen injury criteria can be applied.
Computer simulations – Using the proposed abdomen force / deflection characteristics from the biomechanical tests the abdomen injury criteria can be used in both MADYMO and Finite Element dynamic simulations.
|
Dr. A.R. Payne |
S. Patel |
© MIRA 2001 |
|
Project 427519 |
Version 1.1 |