Durability and Crack Growth Testing

Introduction

Failure in rubber components is difficult to understand. The strain at failure in a tensile test can be at several hundred percent yet the parts in service can fail at strains that are only a fraction of the tensile failure. This may be because cracks that already exist or cracks to initiate and grow and cause a part failure. A couple of experiments that help understand these issues follow.

Tear and Crack Growth Experiments:

Static Tearing Energy

Failure in elastomeric parts is hard to predict and understand. Tensile failure strain data can be very misleading when materials are exposed to cuts or defects. A conservative approach to predicting failure is to use maximum strain, maximum stress and tearing energy information developed in a static tearing energy experiment. In this experiment, a cut is introduced into a planar tension test specimen and stretched until the crack grows. This experiment is often performed at multiple temperatures.

Dynamic Fatigue Crack Growth

The following snapshots show a few of the testing services available to those researching durability and the growth of cracks in elastomeric materials. CCD camera based vision systems have been integrated with digital servohydraulic instruments to provide crack measurements during testing. Crack images are captured at precise strain levels and at preset cyclic intervals and then processed to provide crack width and crack contour measurements along with stress and strain measurements as cyclic loading progresses.