Photoelastic Stress Measurement Experiment Report

Photoelastic Stress Measurement Experiment Report Date: 15th February 2010 Student: Tony Toole Technical Support: Peter Charlton

Abstract The purpose of this experiment was to analyse the stresses on a Perspex component under load conditions. The laboratory exercise was completed via remote access using a student dedicated remote desktop link that formed part of the on-line learning environment. A voice communications link to the laboratory was also used to enable the support of a supervising technician. A Hounsfield Tensile testing machine was used to systematically stress a perspex component while measurements were made using a photoelastic stress analysis system. The measurements were made remotely by VPN connection between the student PC and the PC controlling the equipment in the laboratory. The student provided a series of instructions to the supervising technician to increase the load incrementally and data was captured from the Stress Photonics system for analysis. The technician reported on the deformation and load applied at each incremental change. Apparatus Stress Photonics Photoelastic Stress Analysis System; Hounsfield Tensile Testing Machine; Perspex Component; desktop PC with VPN connectivity. Method A. Start Procedure 1. VPN connectivity to the University Network was established from the remote PC. 2. The Remote Desktop Link from the on-line distance learning website was used to launch the application on the university computer. The normal university user name and password was used to log on. 3. Voice Communications was established with the supervising technician who had already set up the test piece in the tensile testing machine. 5. The Lab technician was asked to ensure that the equipment was properly aligned, the component was under zero load conditions and all equipment was operational. 6. The stress photonics application was launched. 7. The initial calibration and camera set up steps were carried out remotely as described in the equipment instructions.

B. Data Acquisition 1. An image was captured of the of the unloaded component, along with a graph from the stress analysis software. The image data was saved locally on the laboratory PC and the images were saved remotely on the student PC. 2. Requests were made, following each data capture, for the lab technician to increase the compressive load in offset increments of 0.5mm, acquiring and saving image data at each step. The technician was requested to report he respective force applied in newtons at each step and this was recorded. 3. Step 2 above was repeated until an offset value of 5mm had been applied.

C. Data Analysis The maximum shear stress plot option was used in the analysis to note the maximum and minimum shear stresses for each load condition. Note was also taken of the positions of tensile and compression stress regions of the component and the effect each load condition has. The following images provide a sample of the outcomes from the unstressed state to where an offset of 5mm had been applied. 1. Unstressed

2. 0.5mm offset, 8.7 Newton load 3. 1.5mm offset, 27.5 Newton load

4. 3mm offset, 60.5 Newton load

5. 5mm offset, 103.7 Newton load D. Conclusions The outcomes of the experiment show that remote data capture using sophisticated laboratory equipment is straightforward and meets the needs of the course practical work. It can be reported that the capture and graphical presentation of the data was quick, repeatable and consistent throughout the trial. At no time was there a problem with connectivity and there was no perceptible delay as a result of the access being remote at a distance.