Abstract:
A vehicle component test method includes measuring first acceleration data at discrete locations on a first vehicle frame during an actual road test of a first vehicle and measuring second acceleration data at the discrete locations on a second vehicle frame of a second vehicle mounted on a test fixture. The second acceleration data is compared to the first acceleration data and an acceleration error is generated. The test fixture is adjusted based on the acceleration error until the acceleration error is within a predetermined range.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/611,990, filed on Sep. 22, 2004. The disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to vehicle test methods and more particularly to a component test for a truck box or truck cab that can be performed without suspension parts. 
     BACKGROUND OF THE INVENTION 
     During vehicle development, full-vehicle tests are typically performed on prospective vehicles to ensure drivability and durability. Such tests are usually performed using a prototype, fully-assembled, vehicle on various test roads of varying surfaces (i.e., cobblestone, dirt, gravel, etc.). 
     Full-vehicle tests are generally expensive due to high assembly and component costs associated with testing a prototype vehicle. Therefore, individual vehicle components that require testing on a fully-assembled prototype vehicle require a manufacturer to spend more money than would be necessary if the same component could be tested on a separate test fixture. For example, truck boxes and truck cabs can typically only be tested for durability if a vehicle is cycled through either a full-vehicle test on actual test roads or in a laboratory on a full-vehicle test fixture. In this manner, when design changes are made to a truck box or truck cab, full-vehicle tests, complete with suspension components, are often required to properly validate the new design. As such, manufacturers incur high costs in validating individual vehicle components when full-vehicle tests are required. 
     SUMMARY OF THE INVENTION 
     A vehicle component test method includes measuring first acceleration data at discrete locations on a first vehicle frame during an actual road test of a first vehicle and measuring second acceleration data at the discrete locations on a second vehicle frame of a second vehicle mounted on a test fixture. The second acceleration data is compared to the first acceleration data and an acceleration error is generated. The test fixture is adjusted based on the acceleration error until the acceleration error is within a predetermined range. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will become more fully understood from a reading of a detailed description, taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a side view of a test vehicle on a full-vehicle test fixture; 
         FIG. 2  is a perspective view of a front fixture mount of the test vehicle of  FIG. 1 ; 
         FIG. 3  is a perspective view of a rear fixture mount of the test vehicle of  FIG. 1 ; 
         FIG. 4  is a perspective view of the rear fixture mount of  FIG. 3  showing an accelerometer and a load cell; 
         FIG. 5  is an exemplary plot showing an iterative testing process in accordance with the testing method of the invention; 
         FIG. 6  is a flowchart detailing the iterative testing process of  FIG. 5 ; 
         FIG. 7  is an exemplary plot of box strain obtained during a road test; 
         FIG. 8  is a flow chart detailing a drive file development process in accordance with the principles of the invention; 
         FIG. 9  is an exemplary plot comparing box strain as measured during an actual road test versus a box strain as measured using the testing method of the invention; 
         FIG. 10  is an exemplary plot comparing a vertical box load as measured during an actual road test versus a vertical box load as measured using the testing method of the invention; and 
         FIG. 11  is an exemplary plot comparing a box twist as measured during an actual road test versus a box twist as measured using the testing method of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is in no way intended to limit the teachings, application, or uses of the invention. 
     With reference to the drawings, a component test method for use with a full-vehicle test fixture  10  is provided. The full-vehicle test fixture  10  is preferably a MTS 329 or MTS 329LT full-vehicle test fixture, offered by MTS Systems Corporation of Eden Prairie, Minn. The test fixtures  10  are designed to exercise a total vehicle system  12  (i.e., body, frame, and suspension) and are capable of applying up/down, fore/aft, and cross-car forces to the vehicle  12 . The forces applied to the vehicle  12  are intended to mimic actual road data collected on a test road to re-create the road test in a laboratory setting. 
     The exemplary vehicle  12  shown in  FIG. 1  includes a frame  14 , a truck cab  16 , a truck box  18 , and an engine  20 . The vehicle  12  is installed onto one of the MTS fixtures  10  generally at each spindle  22 . A suspension system (not shown) of the vehicle  12  is removed prior to testing to allow simulated road tests to be performed in the laboratory setting independent of the suspension system. The present teachings provides an accurate simulation of an actual road test performed with a vehicle suspension assembled to the vehicle  12  without requiring such suspension system during laboratory testing. 
     The vehicle system is configured as a full-truck inertial-reacted system while the MTS fixture  10  is configured to run in standard matrix control modes. Rear leaf springs (not shown) are removed from the vehicle  12  and replaced with tubing  24 . Existing spring shackles  26  incorporating rubber grommets  28  fixedly attach the tubing  24  to the frame  14  while existing u-bolts  30  fixedly attach a rear axle  32  of the vehicle system  12  to the tubing  24 . 
     Coil springs (not shown) are removed from the suspension system of the vehicle  12  to allow front lower control arms  34  to be fixedly attached to the vehicle  12 . A turnbuckle fixture  38  ( FIGS. 1 and 2 ) is used to maintain a position of the lower control arms  34  relative to the frame  14 . Attachment points between the turnbuckle fixture  38  and the lower control arms  34  utilize rubber grommets  44  to help reduce vibration during testing and to better simulate an actual suspension system. 
     Acceleration, twist, and strain frame data are collected during testing through use of vertical, longitudinal and lateral accelerometers  46  installed at select locations of the vehicle  12  and vehicle frame  14 . Furthermore, frame twist transducers  48  and a box twist transducer  50  ( FIG. 3 ) are installed on the box  18 . The position of the accelerometers  46  on the vehicle  12  and frame  14  during testing on the fixture  10  is determined by the position of the accelerometers  46  during actual road tests. 
     Positioning the accelerometers in such a fashion helps to simulate the actual road test in the laboratory setting. Once the accelerometers are properly installed, acquired data from the laboratory is analyzed for damage contribution with test road segments selected in a fashion that preserve ninety percent or more of the test severity. 
     For example, in one configuration, twenty accelerometers  46  are placed in various locations of the truck frame  14 . The accelerometers  46  are positioned at specific locations on the vehicle frame  14  that correspond to positions used during actual road tests with tri-axial transducers used at each of the four spindle locations  22 . In addition, box and frame twist transducers  48 ,  50  are installed on the box  18  and frame  14 , respectively, using Finite element analysis (FEA) modeling to identify optimum sensor location. Box-mount triaxial load cells  52  may also be installed at each mounting location interface to determine vertical, lateral, and longitudinal loads generally between the box  18  and the frame  14  ( FIG. 4 ). 
     The test method of the invention uses acceleration load cells and twist data as control channels to simulate actual road inputs to the frame  14 . The collected acceleration and twist data is compared to acceleration and twist data from actual road tests to ensure that the input to the vehicle  12  from the fixture  10  is representative of actual road conditions.  FIGS. 5–6  show an exemplary iterative process used to tailor the input to the vehicle  12  such that the vehicle  12  responds in a similar fashion when compared to actual road-test data. 
     The iterative process, or drive-file development (DFD), shown in  FIGS. 5–6  compares actual road data collected during a road test to data collected in a laboratory setting. 
     For example, a force is applied to the test vehicle  12  on the test fixture  10  (i.e., input 1 ). The response of the vehicle is measured via data collected from accelerometers  46  (i.e., lab test data 1 ). The collected data from accelerometers  46  is compared to actual road test data (i.e., road test data 1 ) and an error (i.e. error 1 ) is generated. The iterative process is continued until the outputted error is within an acceptable predetermined range (i.e., generally within eighty to ninety percent of the total severity of the actual road test). When the error is within the predetermined range, the input to the vehicle  12  is considered to be an acceptable approximation of inputs experienced by the vehicle  12  during actual road tests. 
     Data from the accelerometers, transducers, and load cells  46 ,  48 ,  50 ,  52  is analyzed using a Power Spectral Density comparison and a severity analysis process. Test roads with the most damage content are usually chosen for DFD and durability testing. In one example, four data input channels are compared, as best shown in Table 1. In this example, only six out of 23 roads are chosen for DFD and durability testing (i.e., Events  3 ,  12 , and  16 – 19 ). 
     Each of the six chosen roads are filtered to maintain only damaging events so that the test may be performed in a laboratory setting within two weeks. Such testing would typically take between three to six months if actual vehicle testing were required. Power Spectral Density plots for each channel are used to determine frequency ranges for DFD. Generally speaking, frequencies between 0.4 to 40 Hz contain ninety percent of the total severity.  FIG. 7  shows a complete frequency spectrum for one exemplary transducer. 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Retained severity 
               
             
          
           
               
                   
                   
                   
                   
                 Lt Box 
               
               
                 Component box 
                 Box Strain 
                 Rr Frame 
                 Rt Box Mount 
                 Mount 
               
               
                 test 
                 #1 Lt Floor 
                 Twist 
                 #1 Z 
                 #5 Z 
               
             
          
           
               
                 Event 
                 Multiplier 
                 1 
                 4 
                 15 
                 32 
               
               
                   
               
             
          
           
               
                 1 
                 1 
                 0.02% 
                 0.00% 
                 0.04% 
                 0.04% 
               
               
                 2 
                 1 
                 0.67% 
                 0.26% 
                 1.19% 
                 0.86% 
               
               
                 3 
                 1 
                 4.15% 
                 4.95% 
                 2.30% 
                 3.73% 
               
               
                 4 
                 1 
                 0.06% 
                 0.00% 
                 0.09% 
                 0.15% 
               
               
                 5 
                 1 
                 0.00% 
                 0.00% 
                 0.00% 
                 0.01% 
               
               
                 6 
                 1 
                 0.19% 
                 0.00% 
                 0.28% 
                 0.46% 
               
               
                 7 
                 1 
                 0.71% 
                 1.31% 
                 0.64% 
                 0.58% 
               
               
                 8 
                 4 
                 0.01% 
                 0.00% 
                 0.01% 
                 0.05% 
               
               
                 9 
                 3 
                 0.00% 
                 0.00% 
                 0.00% 
                 0.00% 
               
               
                 10 
                 1 
                 0.00% 
                 0.00% 
                 0.00% 
                 0.01% 
               
               
                 11 
                 1 
                 0.00% 
                 0.00% 
                 0.00% 
                 0.00% 
               
               
                 12 
                 1 
                 31.2% 
                 27.9% 
                 43.1% 
                 29.7% 
               
               
                 13 
                 1 
                 0.00% 
                 0.00% 
                 0.00% 
                 0.00% 
               
               
                 14 
                 1 
                 0.00% 
                 0.00% 
                 0.00% 
                 0.00% 
               
               
                 15 
                 1 
                 0.00% 
                 0.00% 
                 0.00% 
                 0.01% 
               
               
                 16 
                 1 
                 22.4% 
                 25.7% 
                 21.4% 
                 18.2% 
               
               
                 17 
                 2 
                 9.70% 
                 10.99%  
                 7.74% 
                 17.39%  
               
               
                 18 
                 1 
                 21.5% 
                 22.2% 
                 17.4% 
                 17.8% 
               
               
                 19 
                 1 
                 4.77% 
                 3.43% 
                 4.52% 
                 6.73% 
               
               
                 20 
                 1 
                 0.11% 
                 0.00% 
                 0.11% 
                 0.34% 
               
               
                 21 
                 1 
                 0.00% 
                 0.00% 
                 0.00% 
                 0.00% 
               
               
                 22 
                 1 
                 4.51% 
                 3.25% 
                 1.11% 
                 3.98% 
               
               
                 23 
                 1 
                 0.00% 
                 0.00% 
                 0.00% 
                 0.00% 
               
             
          
           
               
                 Total severity 
                 100.0%  
                 100.0%  
                 100.0%  
                 100.0%  
               
               
                 Retained 
                 93.7% 
                 95.2% 
                 96.5% 
                 93.5% 
               
               
                 Severity 
               
               
                   
               
             
          
         
       
     
     After editing, each time history is prepared for DFD with each time history being band pass filtered from 0.4 to 40 Hz. During the DFD, the frequency band on several channels can be altered to provide better control of both control and correlation channels. For example, frequency can be controlled within the following frequency ranges at various locations of the vehicle  12 : front vertical frame acceleration: 0.4–40 Hz; rear vertical frame acceleration above the rear axle  32 : 26–32 Hz; rear vertical frame acceleration at a rear spring hanger: 0.4–26 Hz, 32–40 Hz; lateral frame acceleration: 0.4–40 Hz; longitudinal frame acceleration: 0.4–40 Hz; rear frame twist behind a rear cross-member: 0.4–13 Hz. 
     Initially, a seven-by-seven channel square frequency response function (FRF) is chosen as the correction matrix for DFD to reproduce seven primary response signals collected during actual road tests. The seven desired response channels include vertical frame acceleration inboard of each engine mount, vertical frame acceleration above the rear axle  32 , lateral acceleration on the frame  14  above the lower control arms  34  at right front and right rear corners, and longitudinal acceleration above the lower control arms  34  at a left rear corner. Thirty-three additional channels can be retained as secondary responses for correlation during the course of DFD. 
     Following tuning of twelve servo-hydraulic loops (i.e., the test fixture  10 ), MTS RPC Pro Convolution Software can be used to generate shaped white noise for each of the drive channels. Both a single axis x-drive and multi-axis orthogonal drive can be created, for vehicle analysis and modeling. Forty Remote Parameter Control (RPC) response transducers can also be measured. 
     System input channels may include: left front vertical displacement; right front vertical displacement; left rear vertical displacement; right rear vertical displacement; front lateral translation; rear lateral translation; and overall longitudinal translation. 
     Vehicle response channels (i.e., control channels) may include: left front vertical frame acceleration inboard of the engine bracket; right front vertical frame acceleration inboard of the engine bracket; left rear vertical frame acceleration above the rear axle  32 ; right rear vertical frame acceleration above the rear axle  32 ; right front lateral frame acceleration inboard of the engine bracket; right rear lateral frame acceleration above the rear axle  32 ; left rear longitudinal frame acceleration above the rear axle  32 ; left rear vertical frame acceleration behind the rear spring hanger; right rear vertical frame acceleration behind the rear spring hanger; and rear frame twist behind the rear cross-member. 
     Vehicle response channels (i.e., correlation channels) may include: left no.  1  cross-member box vertical load; left no.  1  cross-member box lateral load; left no.  1  cross-member box longitudinal load; right no.  1  cross-member box vertical load; right no.  1  cross-member box lateral load; right no.  1  cross-member box longitudinal load; left no.  6  cross-member box vertical load; left no.  6  cross-member box lateral load; left no.  6  cross-member box longitudinal load; right no.  6  cross-member box vertical load; right no.  6  cross-member box lateral load; right no.  6  cross-member box longitudinal load; box strain gage no.  1 ; box strain gage no.  2 ; box strain gage no.  3 ; box strain gage no.  4 ; box strain gage no.  5 ; box strain gage no.  6 ; box strain gage no.  7 ; box strain gage no.  8 ; bed twist; left front vertical frame acceleration beneath an A-pillar bracket; left front lateral frame acceleration beneath the A-pillar bracket; left front longitudinal frame acceleration beneath the A-pillar bracket; right front longitudinal frame acceleration inboard of the engine bracket; right front vertical frame acceleration beneath the A-pillar bracket; left rear vertical frame acceleration at a front spring hanger; right rear vertical frame acceleration at the front spring hanger; left rear lateral frame acceleration above the rear axle  32 ; and right rear longitudinal acceleration above the rear axle  32 . Box strain gage no.  1 , box strain gage no.  2 , box strain gage no.  3 , box strain gage no.  4 , box strain gage no.  5 , box strain gage no.  6 , box strain gage no.  7 , and box strain gage no.  8  are located in high-stress concentration areas identified by computer modeling. 
     During operation, seven primary channels are extracted from the control channels listed above and several FRF&#39;s are calculated between inputs and outputs to establish the best system model ( FIG. 8 ). FRF&#39;s are reviewed for symmetry, polarities, phasing, etc., and then normalized, inverted, and prepared for DFD. 
     Iterations are commenced on a first road employing the seven-by-seven FRF and are continued until data collected from the control channels in the laboratory adequately approximate data collected during an actual road test. Following this result, thirty-three channels of correlation are measured and reviewed to ensure that the data taken in the laboratory closely approximates actual road data. 
     If the laboratory data does not correlate well with actual road data, additional control channels may be added. For example, a split band iteration approach using a seven-by-nine non-square FRF can be used on the first road in an attempt to provide better correlation for all forty channels. As a result of this approach, a comparison between the loads and strains at the rear of the truck box  18  for a laboratory test and an actual road test are reduced to more acceptable levels. However, some of the box strains and box twist may still read at lower-than-acceptable levels. Under such conditions, a rear frame twist transducer may be added to the current seven-by-nine FRF inverse, as best shown in Table 2. 
     Correlation channels on the truck box  18  are reviewed after each iteration pass. While insertion of the rear frame twist transducer may improve some of the strains, vertical loads, and bed twist on the box  18 , some lateral and vertical loads may achieve higher-than-desired levels. Iterations for the first road may be considered complete when the majority of the correlation channels on the truck box  18  achieve an acceptable level. Examples of correlation for box strains, box vertical load, and box twist shown in  FIGS. 9–11 . 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Response matrix control channel 
               
               
                 Response Control Channels 
               
             
          
           
               
                 7 × 7 FRF 
                 7 × 9 FRF 
                 7 × 10 FRF 
               
               
                   
               
               
                 Left vertical frame 
                 Left vertical frame 
                 Left vertical frame 
               
               
                 acceleration above front axle 
                 acceleration above front 
                 acceleration above front axle 
               
               
                   
                 axle 
               
               
                 Right front vertical frame 
                 Left longitudinal frame 
                 Right front vertical frame 
               
               
                 acceleration above front axle 
                 acceleration above rear 
                 acceleration above front 
               
               
                   
                 axle 
                 axle 
               
               
                 Left vertical frame 
                 Left vertical frame 
                 Left vertical frame 
               
               
                 acceleration above rear axle 
                 acceleration above rear 
                 acceleration above rear 
               
               
                   
                 axle 
                 axle 
               
               
                 Right vertical frame 
                 Right vertical frame 
                 Right vertical frame 
               
               
                 acceleration above rear axle 
                 acceleration above rear 
                 acceleration above rear 
               
               
                   
                 axle 
                 axle 
               
               
                 Right lateral frame 
                 Right lateral frame 
                 Right lateral frame 
               
               
                 acceleration above front axle 
                 acceleration above front 
                 acceleration above front 
               
               
                   
                 axle 
                 axle 
               
               
                 Right lateral frame 
                 Right lateral frame 
                 Right lateral frame 
               
               
                 acceleration above rear axle 
                 acceleration above rear 
                 acceleration above rear 
               
               
                   
                 axle 
                 axle 
               
               
                 Left longitudinal frame 
                 Left longitudinal frame 
                 Left longitudinal frame 
               
               
                 acceleration above rear axle 
                 acceleration above rear 
                 acceleration above rear 
               
               
                   
                 axle 
                 axle 
               
               
                   
                 Left rear spring shackle 
                 Left rear spring shackle 
               
               
                   
                 frame acceleration 
                 frame acceleration 
               
               
                   
                 Right rear spring shackle 
                 Right rear spring shackle 
               
               
                   
                 frame acceleration 
                 frame acceleration 
               
               
                   
                   
                 Rear frame twist 
               
               
                   
               
             
          
         
       
     
     Iteration statistics and severity comparison are shown in Tables 3, 4, and 5. The criterion to stop iterations for each road surface is when the severity comparison between road and laboratory data ranges between sixty to one hundred and forty percent. An arbitrary curve may be developed that allows all transducers to be evaluated for severity using generic stress fatigue algorithms. 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 Iterations statistics 
               
               
                 Pot Holes and Cobble Stone Road 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 RMS 
                 RMS 
                   
               
               
                 Channel 
                 Desired 
                 Achieved 
                 Percent Error 
               
               
                   
               
               
                 Rr Frame Twist 
                 0.04 
                 0.04 
                 −3.3% 
               
               
                 Box Twist 
                 0.05 
                 0.05 
                 −3.1% 
               
               
                 Lt Ft Frame Accel Z Above Axle 
                 0.20 
                 0.22 
                 11.8% 
               
               
                 Rt Ft Frame Accel Y Above Axle 
                 0.21 
                 0.23 
                 14.1% 
               
               
                 Rt Ft Frame Accel Z Above Axle 
                 0.20 
                 0.18 
                 −13.6% 
               
               
                 Lt Rr Frm Accel X Above Axle 
                 0.21 
                 0.22 
                 7.7% 
               
               
                 Lt Rr Frm Accel Z Above Axle 
                 0.29 
                 0.35 
                 18.9% 
               
               
                 Rt Rr Frm Accel Y Above Axle 
                 0.18 
                 0.19 
                 2.3% 
               
               
                 Rt Rr Frame Accel Z Above Axle 
                 0.29 
                 0.37 
                 25.5% 
               
               
                 Lt Rr Spring Shackle Accel Z 
                 0.42 
                 0.43 
                 4.5% 
               
               
                 Rt Rr Spring Shackle Accel Z 
                 0.43 
                 0.46 
                 6.9% 
               
               
                   
               
               
                   
                 Maximum 
                 Maximum 
               
               
                 Channel 
                 Desired 
                 Achieved 
                 Percent Error 
               
               
                   
               
               
                 Rr Frame Twist 
                 0.24 
                 0.24 
                 −1.8% 
               
               
                 Box Twist 
                 0.36 
                 0.34 
                 −4.6% 
               
               
                 Lt Ft Frame Accel Z Above Axle 
                 2.04 
                 1.52 
                 −25.4% 
               
               
                 Rt Ft Frame Accel Y Above Axle 
                 1.68 
                 1.88 
                 12.3% 
               
               
                 Rt Ft Frame Accel Z Above Axle 
                 1.90 
                 1.47 
                 −22.6% 
               
               
                 Lt Rr Frm Accel X Above Axle 
                 1.65 
                 1.69 
                 2.5% 
               
               
                 Lt Rr Frm Accel Z Above Axle 
                 1.92 
                 2.11 
                 10.0% 
               
               
                 Rt Rr Frm Accel Y Above Axle 
                 1.32 
                 1.58 
                 20.1% 
               
               
                 Rt Rr Frame Accel Z Above Axle 
                 1.68 
                 2.27 
                 34.8% 
               
               
                 Lt Rr Spring Shackle Accel Z 
                 2.64 
                 2.51 
                 −4.9% 
               
               
                 Rt Rr Spring Shackle Accel Z 
                 2.42 
                 2.97 
                 22.8% 
               
               
                 Rr Frame Twist 
                 −0.26 
                 −0.25 
                 −5.0% 
               
               
                 Box Twist 
                 −0.36 
                 −0.38 
                 4.1% 
               
               
                 Lt Ft Frame Accel Z Above Axle 
                 −1.80 
                 −1.59 
                 −11.7% 
               
               
                 Rt Ft Frame Accel Y Above Axle 
                 −1.82 
                 −1.93 
                 6.4% 
               
               
                 Rt Ft Frame Accel Z Above Axle 
                 −1.80 
                 −1.41 
                 −21.2% 
               
               
                 Lt Rr Frm Accel X Above Axle 
                 −1.56 
                 −1.49 
                 −4.7% 
               
               
                 Lt Rr Frm Accel Z Above Axle 
                 −1.82 
                 −2.00 
                 10.3% 
               
               
                 Rt Rr Frm Accel Y Above Axle 
                 −1.55 
                 −1.75 
                 12.8% 
               
               
                 Rt Rr Frame Accel Z Above Axle 
                 −1.76 
                 −2.15 
                 22.4% 
               
               
                 Lt Rr Spring Shackle Accel Z 
                 −2.34 
                 −2.19 
                 −6.7% 
               
               
                 Rt Rr Spring Shackle Accel Z 
                 −2.40 
                 −2.43 
                 0.9% 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Iterations severity comparison 
               
               
                 Percent Severity Contribution Edited (Road) 
               
             
          
           
               
                   
                   
                   
                 Rt. 
                 Lt. 
                   
               
               
                   
                 Rr 
                   
                 Box 
                 Box 
                 Box 
               
               
                   
                 Frame 
                 Box 
                 Mount 
                 Mount 
                 Strain 
               
               
                 Road Event 
                 Twist 
                 Twist 
                 no. 1 Z 
                 no. 5 Z 
                 no. 1 
               
               
                   
               
               
                 Gravel Road 
                  5% 
                  5% 
                  4% 
                  5% 
                  4% 
               
               
                 Sine Wave &amp; Washer 
                 30% 
                 34% 
                 32% 
                 20% 
                 33% 
               
               
                 Board 
               
               
                 Potholes - Passengers 
                 26% 
                 26% 
                 20% 
                 27% 
                 24% 
               
               
                 Side 
               
               
                 Gravel Road (ungraded) 
                 10% 
                  7% 
                 18% 
                 18% 
                 10% 
               
               
                 Truck Potholes - Drivers 
                 23% 
                 23% 
                 19% 
                 23% 
                 23% 
               
               
                 side 
               
               
                 Pot Holes &amp; Cobble 
                  6% 
                  5% 
                  7% 
                  7% 
                  5% 
               
               
                 Stones 
                   
               
               
                 Percent Severity Baseline 
                 100%  
                 100%  
                 100%  
                 100%  
                 100%  
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Iterations severity comparison 
               
               
                 Percent Severity Contribution Achieved (Lab) 
               
             
          
           
               
                   
                   
                   
                 Rt. 
                 Lt. 
                   
               
               
                   
                 Rr 
                   
                 Box 
                 Lt. Box 
                 Box 
               
               
                   
                 Frame 
                 Box 
                 Mount 
                 Mount 
                 Strain 
               
               
                 Road Event 
                 Twist 
                 Twist 
                 no. 1 Z 
                 no. 5 Z 
                 no. 1 
               
               
                   
               
               
                 Gravel Road 
                  3% 
                  3% 
                  5% 
                  7% 
                  6% 
               
               
                 Sine Wave &amp; Washer 
                 26% 
                 15% 
                 33% 
                 55% 
                 33% 
               
               
                 Board 
               
               
                 Potholes - Passengers 
                 22% 
                 17% 
                 35% 
                 36% 
                 45% 
               
               
                 Side 
               
               
                 Gravel Road (ungraded) 
                  7% 
                  7% 
                  7% 
                 12% 
                  9% 
               
               
                 Truck Potholes - Drivers 
                 18% 
                 14% 
                 25% 
                 25% 
                 24% 
               
               
                 side 
               
               
                 Pot Holes &amp; Cobble 
                  6% 
                  5% 
                  7% 
                  9% 
                  6% 
               
               
                 Stones 
                   
               
               
                 Percent Severity Achieved 
                 83% 
                 61% 
                 112%  
                 144%  
                 122%  
               
               
                   
               
             
          
         
       
     
     Development methods using frame twist and box loads in conjunction with frame acceleration (i.e., seven-by-ten non-square FRF) generally provide the best results for truck box component testing than development methods where only frame acceleration (i.e., seven-by-seven square FRF) is used. Furthermore, correlation strain levels are reproduced better with a seven-by-ten non-square FRF. Therefore, durability tests show the best correlation between actual on-road tests and simulated laboratory tests using drive files developed with a seven-by-ten non-square FRF. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.