Gear geometry and contact patterns

When all calculations and tests are completed, you need to form one or more hypotheses for the probable cause of failure, then determine if the evidence supports or disproves the hypotheses. Here, you need to evaluate all of the evidence that was gathered including:

• Documentary evidence and service history.

• Statements from witnesses.

• Written descriptions, sketches, and photos.

• Gear geometry and contact patterns.

• Gear design calculations.

• Laboratory data for materials and lubricant.

Results of this evaluation may make it necessary to modify or abandon the initial hypotheses. Or, pursue new lines of investigation.

Finally, after thoroughly testing the hypotheses against the evidence, you reach a conclusion about the most probable cause of failure. In addition, you may identify secondary factors that contributed to the failure.

A failure analysis report should describe all relevant facts found during the analysis, the inspections and tests, weighing of evidence, conclusions, and recommendations. Present the data succinctly, preferably in tables or figures. Good photos are especially helpful for portraying failure characteristics.