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 SAE
Heavy Truck Crashworthiness
Exponent was selected to conduct the background research and
develop test procedures that could be used to evaluate heavy
truck occupant protection for certain classes of typically
fatal accident scenarios that were considered potentially
survivable. Phase I of this program was a study to identify
the kind of injurious accidents that were occurring. From
this study, deceleration time histories were developed that
best characterized the accident scenarios producing heavy
truck occupant fatalities. Also developed in Phase I was the
capability of simulating occupant dynamics in heavy truck
crashes using the characteristic crash pulses. Phase II of
this program was aimed at develop-ing tools that could be
used to analytically evaluate designs for occupant protection.
In Phase III, test procedures for evaluating heavy truck occupant
protection were developed. The resulting procedures evaluate
the heavy truck restraint systems, cab interior components,
and cab structural integrity. As much as possible, these test
procedures were configured to simulate components of the accident
scenarios found in Phase I. As a result of this work, a number
of new SAE Recommended Practices were adopted.
Vehicle Evaluation And Testing
To accommodate different engine and transmission combinations
a garbage truck manufacturer flame cut the top flange section
of the frame rails just aft of the engine support cross member.
In addition to trash collection, these trucks were also used
to plow snow in the winter months. The manufacturer did not
relieve the stress concentrations created by the flame-cutting,
nor did they reinforce the frame rail to compensate for the
loss in strength due to the reduced section modulus. After
several years of service, the fleet operator’s maintenance
personnel began to discover cracks in the frame rails.
 Exponent
was asked by the fleet operator (client) to verify that the
recommended repair that was currently underway was sufficient
for the remaining service life of their garbage truck fleet.
To answer this question with confidence and to prepare for
the possibility that the proposed fix was not sufficient,
Exponent engineers built and validated a Finite Element Model
(FEM) of the frame rail structure. The front and rear suspension
systems were modeled and their stiffness characteristics were
measured. A modal analysis was conducted on the front suspension
to determine the natural frequency characteristics of the
front suspension. Strain gages were installed to quantify
the stress field in the areas where the cracks in the flange
originated and the truck was instrumented with uniaxial accelerometers.
A complete time history of the strain and accelerometer data
was collected for a typical refuse collection cycle. Fifteen
controlled truck maneuvers were conducted, with and without
a snow plow attached. Based on these tests, Exponent determined
that the predicted crack growth and stresses in the repaired
frame rails did not present a safety concern for the trucks
to be used for the remainder of their intended service life.
As a result of this project, the client has hired Exponent
to review a number of their vehicle design specifications
and conduct inspections of new fleet vehicles.
Vehicle Selection, Specification, and Acquisition
 Exponent
performs vehicle selection, specification, and acquisition
reviews for clients to aid in determining the best vehicle
or equipment based on specified parameters, including optimal
service life. As a result, our analyses provide our clients
savings on initial cost, higher resale values, greater driver/operator
satisfaction, reduced downtime, reduced warranty work, and
improved safety. With the increasing importance of federal,
state and local regulations, standards, and testing requirements,
Exponent offers investigation, assessment, and evaluation
of all technical requirements to help our clients efficiently
compete in today’s world market.
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