Quick Look
Direct Measurement of Operational Induced Strain Using
Laser-Embossed Parts Marking, 18-9549
Principal Investigators
John C. Simonis
Ernest Franke
Peter C. McKeighan
Laura L. Bequette
Inclusive Dates: 06/27/05 – Current
Background - The purpose of the project is to evaluate the sensitivity, reliability, and accuracy of the strain measurement obtained from displacement measurements using embossed parts marking and a laser displacement measuring system.
Approach - Techniques using grids or patterns projected onto a surface have long been used to measure strain in a mechanical part. However, no reference research is being done to measure the strain in parts using parts marking codes or other forms of laser-embossed markings. Strain in a part using full field techniques is evaluated by measuring the finite, but small, displacement of an embossed pattern caused by the applied loads. The displacements have in the past been determined by measuring the displacement of a regular geometric or dot matrix pattern embossed on the surface of a part before external loads strain the part, and then remeasuring this pattern after the external loads have been applied.
Accomplishments - To date, fifteen tensile specimens have been marked using Army-approved Laser Dot Matrix and Dot Peening processes. The test specimens were serialized and are currently undergoing strain testing. Two specimens have been strained and measurements have been taken. Based on the initial data, the results look encouraging. If the proposed technique to determine strain using laser measurements of displaced features of an embossed parts mark is successful, then it will find wide military and commercial applications.
For military applications, this technique can be used to passively determine the fatigue damage and estimate the residual life of flight critical parts. The pilot's log or other tracking documents can be used to determine the number of hours the part has been in service. Dynamic analysis of the system is used to determine the number of cycles for each flight hour. Thus, the estimated total number of cycles that have acted on a part can be estimated. This result, coupled with the measured strain and strain life prediction methods, will result in an estimate of the remaining residual life of the part.
For commercial applications, machinery usage records can be used to estimate the hours that the part has been in service. Applying the technology to factory equipment will allow commercial organizations to better predict the residual life of machine parts, thereby reducing unplanned breakdowns and equipment outages and greatly reducing impacts on production line downtimes that ultimately increase their financial "bottom lines."
