| Abstract | When a vehicle collides with a barrier it undergoes rapid deceleration. This deceleration ‘pulse’ can be characterised by parameters including velocity change, duration, average deceleration, peak deceleration and shape. As impact speed changes, these parameters also change. This thesis proposes that the vehicle crash pulse parameters result from a fundamental underlying physical process that can be modelled mathematically. In such a
model, the relationship between impact energy and the pulse is causal, and can be expressed as a differential equation with parameters dependent on inherent properties of the vehicle crash structure. A model based on this relationship may be useful for vehicle crash pulse modelling. If the crash pulse characteristics of a vehicle impacting a barrier at a certain speed are known, those characteristics may be used in combination with such a model to predict crash pulse characteristics at other speeds. In this thesis, models of vehicle crash pulses are examined, including models which describe pulse shape or parameterise crash pulses. The theory of a causal model is explored that relates the square root of impact energy to maximum deformation and time of maximum deformation through power-law equations, with exponents that parameterise the non-linearity of the relationships. The causal model is applied to three sets of full width rigid barrier frontal crash tests: - Modern vehicles of similar category, size, weight and construction method, allowing the causal model to be analysed using a reasonably homogeneous data-set. - Modern vehicles of varying category, construction method, size and weight, allowing the effect of variation in vehicle characteristics on the exponents of the model to be assessed. - Tests of a single vehicle over a large range of impact speeds, allowing some analysis of the causal model at speeds higher than regulatory crash test speeds. For each set, appropriate tests are identified and selected. Test parameters, vehicle characteristics and acceleration data are collected. Acceleration data is filtered; offsets calculated and applied; vehicle kinematics calculated; and crash pulse parameters calculated. The crash pulse parameters are used with the causal model to estimate exponents for the relationship between the square root of impact energy and maximum deformation. Vehicle-specific exponents are estimated; common exponents are estimated for groups of vehicles based on their category, size, and construction method; and a common exponent is estimated for the whole set. The relationship between the exponent and the characteristics of the vehicle is then examined, specifically the relationship between the exponent and the vehicle size, weight, category, crash structure dimensions, and method of construction. The relationship between the exponent and the crash pulse shape, specifically the pulse loading in the deformation phase, is also examined. Analysis of the tests suggests that the vehicle construction method affects the exponent of the equation relating the square root of impact energy and maximum deformation. Observations imply an approximately proportional relationship (common exponent near 1) for unibody vehicles; and a greater-than-proportional increase in deformation (common exponent near 1.4) for body on- frame vehicles. Some vehicle-specific exponents differ significantly from the common exponent for similar vehicles. |
