Chris Gearhart

Approving Measurement Systems When Using Derived Values

This article presents a methodology for approving a measurement system when the variable of interest is not directly measured. Rather, the manufacturer measures some other related variables to derive or predict the quality characteristic. To approve the measurement system, one must estimate error in each measured value and then, using either variable transformation or a Taylor series approximation, propagate these errors through the calculation to obtain an error distribution for the derived values. An evaluation of a measurement system used to measure the friction of automotive brake pads—derived from force and torque measurements—demonstrates the methodology.

Recent progress in crash pulse analysis

The deceleration of the occupant compartment of a vehicle during a crash, also known as the crash pulse, is of central importance in the analysis of vehicle safety. The crash pulse is used to assess the crashworthiness of the vehicle structure and as input to occupant injury models. This paper provides a brief historical review of crash pulse analysis based on simple polynomial and Fourier characterisations, and presents some recent developments in experimental crash pulse characterisation based on statistical wavelet analysis. A simple formalism for decomposing the crash pulse, obtained from computational models, into component contributions is discussed and analysed for a simple spring-mass model of vehicle structure. Implications for more detailed models are discussed. Finally, a possible method for connecting occupant injury to the component level crash pulse contributions is presented.

Using dimensional analysis to build a better transfer function

A key ingredient in designing products that are more robust is a thorough knowledge of the physics of the ideal function of those products and the physics of the failure modes of those products. We refer to the mathematical functions describing this physics as the transfer functions for that product. Dimensional analysis (DA) is a well known, but often overlooked, tool for reducing the number of experiments needed to characterize a physical system. In this paper, we demonstrate how the application of DA can be used to reduce the size of a DOE needed to estimate transfer functions experimentally. Furthermore, the transfer function generated using DOEs with DA tend to be more general than those generated using larger DOEs directly on the design parameters. With ever-increasing competitive pressure and reduced product development time, a tool such as DA, which can dramatically reduce experimental cost, is an incredibly valuable addition to an engineers toolbox.

Model of IIHS side impact torso response measures using transfer function equations

Vehicle to vehicle crash compatibility is becoming an increasingly more important consideration during vehicle safety development due to the increasing numbers of SUVs and pickups in the vehicle fleet. According to the Insurance Institute for Highway Safety (IIHS), their side impact crash test represents what happens when a passenger vehicle is struck by a pickup truck or SUV. The IIHS side impact test measures 37 different response criteria using an instrumented 5 th percentile female SID-lls ATD (anthropomorphic test device) in driver and left rear passenger seats. These measures are grouped into head and neck, torso, and pelvis and left leg regions. This paper will describe the development of transfer function equation models to assess the performance of design countermeasures by comparing the response measures of the torso region of the body. This transfer function model will be a useful tool in determining the significance of certain design parameters and making performance comparisons of design proposals. This tool will also allow safety engineers to experiment with various designs in the early stages of the development of the side impact countermeasures.