CHAPTER 9

Test Conditions

Test Facility

The full-scale crash tests reported herein were performed at the TTI Proving Ground, an International Organization for Standardization (ISO)/International Electrotechnical Commission (IEC) 17025–accredited laboratory with American Association for Laboratory Accreditation (A2LA) Mechanical Testing Certificate 2821.01. The full-scale crash tests were performed according to TTI Proving Ground quality procedures as well as MASH guidelines and standards.

The test facilities of the TTI Proving Ground are located on the RELLIS Campus of the Texas A&M University System, which consists of a 2,000-acre complex of research and training facilities situated 10 mi northwest of the flagship campus of Texas A&M University. The site, formerly a U.S. Army Air Corps base, has large expanses of concrete runways and parking aprons well suited to experimental research and testing in the areas of vehicle performance and handling, vehicle–roadway interaction, highway pavement durability and efficacy, and roadside safety hardware and perimeter protective device evaluation. The site selected for construction and testing is along the edge of an out-of-service apron/runway. The apron/runway consists of an unreinforced jointed-concrete pavement in 12.5- × 15-ft blocks nominally 6 in. deep. The aprons were built in 1942, and the joints have some displacement but are otherwise flat and level.

Vehicle Tow and Guidance System

For the testing utilizing the 1100C and 2270P vehicles, each vehicle was towed into the test installation with a steel cable guidance and reverse tow system. A steel cable for guiding the test vehicle was tensioned along the path, anchored at each end, and threaded through an attachment to the front wheel of the test vehicle. An additional steel cable was connected to the test vehicle, passed around a pulley near the impact point and through a pulley on the tow vehicle, and then anchored to the ground, such that the tow vehicle moved away from the test site. A 2:1 speed ratio between the test and tow vehicle existed with this system. Just prior to impact with the installation, the test vehicle was released and ran unrestrained. The vehicle remained freewheeling (i.e., no steering or braking inputs) until it cleared the immediate area of the test site.

Data Acquisition Systems

Vehicle Instrumentation and Data Processing

Each test vehicle was instrumented with a self-contained onboard data acquisition system (DAS). The signal conditioning and acquisition system was a multichannel DAS produced by Diversified Technical Systems Inc. The accelerometers, which measure the x, y, and z axes of

vehicle acceleration, were strain gauge type with linear millivolt output proportional to acceleration. The angular rate sensors measuring vehicle roll, pitch, and yaw rates were ultra-small, solid-state units designed for crash test service. The data acquisition hardware and software conformed to the latest SAE J211, Instrumentation for Impact Test. Each of the channels was capable of providing precision amplification, scaling, and filtering based on transducer specifications and calibrations. During the test, data were recorded from each channel at a rate of 10,000 samples per second with a resolution of one part in 65,536. Once data were recorded, internal batteries backed these up inside the unit in case the primary battery cable were to be severed. Initial contact of the pressure switch on the vehicle bumper provided a time zero mark and initiated the recording process. After each test, the data were downloaded from the DAS unit into a laptop computer at the test site. The TRAP software then processed the raw data to produce detailed reports of the test results.

Each DAS is returned to the factory annually for complete recalibration and to ensure that all instrumentation used in the vehicle conforms to the specifications outlined by SAE J211. All accelerometers are calibrated annually by means of an Endevco^® 2901 precision primary vibration standard. This standard and its support instruments are checked annually and receive a National Institute of Standards Technology (NIST) traceable calibration. The rate transducers used in the data acquisition system receive calibration via a Genisco Rate-of-Turn Table. The subsystems of each data channel are also evaluated annually with instruments with current NIST traceability, and the results are factored into the accuracy of the total data channel per SAE J211. Calibrations and evaluations are also made any time data are suspect. Acceleration data are measured with an expanded uncertainty of ±1.7% at a confidence factor of 95% (k = 2).

TRAP uses the DAS-captured data to compute the occupant/compartment impact velocities, time of occupant/compartment impact after vehicle impact, and highest 10-millisecond (ms) average ridedown acceleration. TRAP calculates change in vehicle velocity at the end of a given impulse period. In addition, maximum average accelerations over 50-ms intervals in each of the three directions are computed. For reporting purposes, the data from the vehicle-mounted accelerometers are filtered with an SAE Class 180-Hz low-pass digital filter, and acceleration versus time curves for the longitudinal, lateral, and vertical directions are plotted with TRAP.

TRAP uses the data from the yaw, pitch, and roll rate transducers to compute angular displacement in degrees at 0.0001-s intervals and then plots yaw, pitch, and roll versus time. These displacements are in reference to the vehicle-fixed coordinate system with the initial position and orientation being initial impact. The rate of rotation data is measured with an expanded uncertainty of ±0.7% at a confidence factor of 95 percent (k = 2).

Anthropomorphic Dummy Instrumentation

An Alderson Research Laboratories Hybrid II, 50th-percentile male anthropomorphic dummy restrained with lap and shoulder belts was placed in the front seat on the impact side of the 1100C vehicle. The dummy was not instrumented.

According to MASH, use of a dummy in the 2270P vehicle is optional. However, MASH recommends that a dummy be used when testing “any Longitudinal Barrier with a height greater than or equal to 33 in.” More specifically, use of the dummy in the 2270P vehicle is recommended for tall rails to evaluate the “potential for an occupant to extend out of the vehicle and come into direct contact with the test article.” Although this information is reported, it is not part of the performance evaluation of the impact. Since the rail height of the multifunctional barrier was 41 in., a dummy was placed in the front seat of the 2270P vehicle on the impact side and restrained with lap and shoulder belts.

Photographic Instrumentation Data Processing

Photographic coverage of each test included three digital high-speed cameras:

• One located overhead with a field of view perpendicular to the ground and directly over the impact point,
• One placed upstream from the installation at an angle to have a field of view of the interaction of the rear of the vehicle with the installation, and
• A third placed with a field of view parallel to and aligned with the installation at the downstream end.

A flashbulb on the impacting vehicle was activated by a pressure-sensitive tape switch to indicate the instant of contact with the installation. The flashbulb was visible from each camera. The video files from these digital high-speed cameras were analyzed to observe phenomena occurring during the collision and to obtain time event, displacement, and angular data. A digital camera recorded and documented the conditions of each test vehicle and the installation before and after the test.