Reducing Stress Concentrations

Overview

Beaumont Technologies presented an opportunity to study the impact of stress concentrations on polymers. Stress concentrations can cause premature failure of plastic parts, shortening expected life of products and creating dangerous points of failure. This team was presented with the challenge of studying geometries that create stress concentrations on numerous polymers, tensile testing them to failure, then analysing the effects on the specimens.

Objectives

• Injection mold test specimens of four stress concentrations into four polymer materials. 
• Tensile test specimens to create stress vs strain curves. 
• Analyse percent change and trends of geometries and materials.

Approach

• Research into the fundamental concepts of stress concentrations in part design and polymers. 
• CAD models were developed to produce drawings for machining changes in tooling. 
• Materials were conditioned and molded using formulaic processing methods. 
• Tensile testing method developed with adherences to ASTM standards. 
• Stress v. strain material characterization data recorded on tensile software. 
• Data was collected, cleaned, and displayed on Excel to show differences in sample characteristics. 

• Average data was used to extrapolate trends between materials and stress concentrated samples. 
• ANSYS simulation software was utilized to validate recorded data in complimentary fashion. 
• Study of cut-in v. molded-in notch of samples conducted to observe effects of secondary processes. 
• DSC tests used to observe any processing differences between stressed and unstressed samples. 

• Results generated from studies both proved and disproved various elements of the hypothesis. 

Outcomes

• Reduced testing while increasing part design. 
• Aiding in design by having tangible data. 
• Created future work for more data to create a workbook of guidelines.