Simulation 2: Midwest Roadside Safety Facility Crash Test TL5CMB-2
The geometry of the tractor FE model was modified such that the wheelbase of the model was the same as the wheelbase of the test vehicle used in MwRSF Test No. TL5CMB-2. FE analysis was conducted simulating this test using the tractor-semitrailer FE model (model versions tractor_10-0520 and trailer_10-0521). The friction between the tractor and barrier was set to 0.2, and the friction between the tires and the barrier was set to 0.65. The dimensions of the barrier model were the same as those of the barrier in MwRSF Test No. TL5CMB-2 shown in Figure 1. Since there was negligible deflection of the barrier in the full-scale test, the barrier was modeled as a rigid material with rigid fixity to the ground. The impact conditions for the FE simulation were consistent with those reported in the full-scale crash test (i.e., 52.7 mph (84.9 km/hr) at an impact angle of 15.4 degrees).
The ADAP program was used to aid in the modification of overall vehicle model size and shape parameters (e.g., wheelbase, trailer length). These scripts were designed to operate on the FE model input file directly and were used to modify the tractor model geometry. The ADAP scripts were used to: 1) make the sleeper-cab tractor a day-cab style tractor by removing the sleeper section of the cabin and 2) adjust the wheelbase length of the tractor by removing a section of the frame rails (along with other components in this section of the model).Visual comparison between the tractor FE model and the test tractor
The most notable differences between the test vehicle and modified FE model are:
- Length dimensions – The length dimensions of the FE model were all within 2% of the test vehicle dimensions, except for the distance from the front bumper to the center of the front wheel (e.g., dimension “B” in Figure 5), which was 13.5% shorter in the FE model.
- Trailer box dimensions – The trailer floor in the FE model was 5.8 inches (148 mm) higher than the test vehicle (e.g., dimension “L” in Figure 5), and the top of the trailer in the FE model was 6.7 inches (169 mm) lower than the test vehicle (e.g., dimension “W” in Figure 5).
- Ballast center of gravity (c.g.) – The c.g. of the ballast in the FE model was located 23.6 inches (600 mm) rearward of and 4.6 inches (188 mm) higher than the c.g. location of the ballast in the test vehicle.
- Trailer suspension – The suspension system on the FE trailer model was the Airide™ design, and the suspension on the trailer test vehicle was a leaf-spring design.
Although the mass of the test tractor was not reported, it was estimated to be 15,526 lb (7,043 kg) by considering that the total gross static mass of the test vehicle was 28,819 lb (13,073 kg) and that the typical mass of a 48-ft (14.6-m) semitrailer is approximately 13,300 lb (6,030 kg). For comparison, the mass of the FE tractor model was 15,271 lb (6,927 kg). The axle loads of the FE model were within 10% of the axle loads measured on the test vehicle. The total mass of the FE tractor-semitrailer model was 79,807 lb (36,200 kg), which was 0.1% higher than the total mass of the test vehicle.
The analysis was conducted with a time-step of 1.20 microseconds for a time period of 3.0 seconds.
The suspension systems on the tractor and trailer models were initialized based on the weight of the model; however, the model was not at steady state at the beginning of the analysis. The tractor-semitrailer model was positioned at 15.4 ft (4.7 m) upstream of the impact point at the start of the analysis to allow 0.2 seconds for gravity to sufficiently load the suspension of the tractor and trailer prior to impact. The trailer’s response is somewhat affected by the additional vertical dynamics associated with the sudden ‘drop’ of the ballast under gravity.
Movies
 Front view (2.9MB) |  Rear view (2.9MB) |
 Side view (2.9MB) |  Top view (2.8MB) |
 Combined view front (0.3MB) |  Combined view rear (0.2MB) |
Simulation 3: Texas Transportation Institute Test 7069-13
The geometry of the tractor FEM model was modified such that the wheelbase of the model was the same as the wheelbase of the test vehicle used in TTI Test No. 7069-13. An FEM analysis was conducted simulating this test using the Phase C tractor-semitrailer FE model. The friction between the tractor and barrier was set to 0.2, and the friction between the tires and the barrier was set to 0.65. The dimensions of the barrier model were the same as those of the barrier in TTI Test No. 7069-13. Since there was negligible deflection of the barrier in the full-scale test, the barrier was modeled as a rigid material with rigid fixity to the ground. Recall that the purpose of the analysis was to verify the response of the vehicle, which is why the project team selected only full-scale tests in which barrier deflection was minimal. The impact conditions for the FEM simulation were consistent with those reported in the full-scale crash test (i.e., 51.4 mph (82.7 km/hr) and 16.2 degrees).
The ADAP program described in the Phase B final report was developed to aid in the modification of overall vehicle model size and shape parameters (e.g., tractor wheelbase and trailer length). These scripts were designed to operate on the FE model input file directly and were used in this case to modify the model’s dimensions to conform to those of the test vehicle.
In particular, they were used to: 1) make the tractor a day-cab style tractor by removing the sleeper section of the cabin and 2) adjust the wheelbase length of the tractor by removing a section of the frame rails (along with other components in this section of the model). Figure 35 shows a visual comparison between the tractor FE model and the test tractor.
A comparison of the dimensional properties of the FE model to the test vehicle
The content, dimensions and restraint of the ballast were not provided in the test report. Since there were not sufficient details regarding the makeup of the ballast structure in Test 706913, the research team used the ballast model from the MwRSF test simulation. The ballast model was modified to attain the mass of the test-ballast by removing a row of portable concrete barriers (PCB) at the rear of the trailer and reducing the density of the remaining PCB units.
The test inertial mass of the tractor was reported to be 15,010 lb (6,808 kg) and that of the 45-ft (13.7-m) semitrailer was 12,680 lb (5,752 kg). For comparison, the mass of the FE tractor model was 15,507 lb (7,034 kg) and the mass of the FE trailer model was 13,126 lb (5,954 kg). The loads on the front axle in the FE model were 13.5% higher than those of the test vehicle; the loads on the tractor tandems in the FE model were 4% less than those of the test vehicle; and the loads on the trailer tandems in the FE model were 3.5% higher than those of the test vehicle. The total mass of the FE tractor-semitrailer model including trailer ballast was 50,977 lb (23,124 kg), which was 1.85% higher than the total mass of the test vehicle, which was 50,050 lb (22,702 kg).
The most notable differences between the test vehicle and modified FE model are listed below:
- Length dimensions – The length dimensions of the FE model were all within 7.5% of the test vehicle dimensions, except for the distance from the front bumper to the center of the front wheel, which was 44.2% longer in the FE model.
- Trailer box dimensions – The trailer floor in the FE model was 3.0 inches (76.2 mm) higher than the test vehicle (e.g., dimension “L” in Figure 36), and the top of the trailer in the FE model was 9.0 inches (228 mm) lower than the test vehicle.
- Trailer suspension – The suspension system on the FE trailer model was an air-spring design, and the suspension on the trailer test vehicle was a leaf-spring design.
- Tractor-Semitrailer Weight – The FE model of the tractor was approximately 500 lbs heavier than the test tractor, and the FE model of the semitrailer was approximately 400 lbs heavier than the test semitrailer.
- Ballast – The properties, dimensions and restraint of the ballast were not provided in the test report; thus a modified version of the ballast model from the MwRSF test simulation was used.
- Propulsion – The test vehicle was under engine power with drive train engaged for the duration of the impact event. The analysis model was not.
The analysis was conducted with a time-step of 1.20 microseconds for a time period of 3.0 seconds. Prior to the analysis, the model was set at equilibrium with respect to gravity, i.e., the geometry and stresses in all parts of the tractor-trailer model were at equilibrium with gravity. The basic procedure was to 1) conduct an analysis involving the vehicle subjected to only gravity load, 2) save node and element information (e.g., nodal coordinates and element stresses) from the gravity analysis, and 3) include them in subsequent analyses as part of the initial conditions for the model.
Movies
 Front view (2.1MB) |  Rear view (2.2MB) |
 Side view (2.2MB) |  Top view (2.2MB) |
 Combined view (0.3MB) |
