Load Cell Analysis

Description

Load Cell Analysis evaluates force distribution and vehicle compatibility measures from a load-cell-wall crash test. It combines wall forces with a vehicle acceleration channel to describe impact force, impulse, height of force, stiffness, velocity, displacement, energy, and work [1] [2] [3] [4].

When this feature is available

Load Cell Analysis becomes available when either the current curve selection or at least one loaded vehicle test meets the requirements.

For a test to pass:

• The loaded test must be a vehicle test.
• The test must contain at least one load-cell force channel with units NEWTONS.
• The test must contain at least one acceleration channel with:
  • Axis: X - GLOBAL
  • Units: G'S
  • An attachment containing SEAT, FLOORPAN, or SILL
• Both channels must use the NOT APPLICABLE sensor location and a usable data status.

WebSAT enables Load Cell Analysis when the required force and vehicle-acceleration inputs are present. Wall geometry and vehicle and test information are also needed for a complete analysis, while wall moment channels are not part of the requirements.

Settings

This feature has no settings. Wall layout, vehicle mass, impact velocity, and channel locations are read from the loaded test information.

How WebSAT processes the data

1. Organize the barrier load-cell channels by wall row and column.
2. Convert the inputs to consistent units and apply the required filtering.
3. Sum the individual cell forces to obtain total wall force.
4. Integrate force over time to calculate impulse.
5. Calculate the time-varying average height of force:

$AHOF(t)=\frac{\sum_i F_i(t)h_i}{\sum_i F_i(t)}$

6. Derive vehicle velocity and displacement from the selected vehicle acceleration.
7. Evaluate average height of force through 400 mm of vehicle displacement and calculate its variability.
8. Calculate force-displacement work, initial stiffness, and:

$Kw400=\frac{2\int_{25}^{400}F(d)\,dd}{400^2-25^2}$

9. Prepare vehicle and occupant response comparisons when occupant channels are available.
10. Report the wall-force, impulse, AHOF400, stiffness, work, and comparison results.

How to interpret the results

Load Cell Analysis does not apply an occupant IARV or AIS risk function. AHOF400, force distribution, and stiffness are compatibility descriptors; interpret them with the crash configuration and compatibility procedure used for the test [1] [2] [3] [4].

Results

The summary reports the vehicle, test performer, barrier layout, wall dimensions, initial velocity, AHOF400 values and standard deviation, initial stiffness, and Kw400. The following examples show the populated graphs produced for a loaded load-cell-wall test. Vehicle-versus-occupant plots are also available when the test contains a qualifying occupant signal.

Load Cell Analysis summary table with the reported wall and vehicle metrics.

Load-cell wall force distribution at the selected event time.

Load-cell wall impulse distribution.

Summed force histories for the instrumented wall rows.

Summed force histories for the instrumented wall columns.

Total barrier-force history calculated from the load-cell wall.

Vehicle acceleration histories selected for the analysis.

Vehicle velocity histories derived from acceleration.

Vehicle displacement histories derived from velocity.

Vehicle kinetic energy, barrier work, and total energy histories.

Barrier force plotted against calculated vehicle displacement.

Time-varying height of force and the calculated AHOF values.

Height of force plotted against vehicle displacement.

Initial stiffness fits shown on the barrier force–displacement response.

References

[1] Digges, K. and Eigen, A. “Measurements of Stiffness and Geometric Compatibility in Front-to-Side Crashes.” National Crash Analysis Center, George Washington University, Paper 349.

[2] Takizawa, H., Higuchi, K., Iwabe, T., Kisai, A., and Suzuki, K. “Study of Load Cell MDB Crash Tests for Evaluation of Frontal Impact Compatibility.” Paper 05-0235.

[3] Jerinsky, M. and Hollowell, W. “NHTSA's Review of High-Resolution Load Cell Walls' Role in Designing for Compatibility.” National Highway Traffic Safety Administration, Paper 393.

[4] Jerinsky, M. and Hollowell, W. “NHTSA's Review of Vehicle Compatibility Performance Metrics Through Computer Simulation.” IMECE2003-44045.