Avoiding product failure is the mission of everyone involved in engineering and manufacturing. “What must the part do in service?” is a question that needs to be answered when designing any component or system. This leads to the establishment of the engineering requirements that will allow the product to perform its intended function. In manufacturing we ask ourselves, “How was or should the part be made?” Finally, understanding the circumstances under which a part may or did fail is a necessary step in the process. Let’s learn more.

Failures can be traced to deficiencies in design, materials, processing, product characteristics and quality, known and unknown application factors, and to human error. Examples include excessive distortion, buckling, ductile or brittle fracture, creep, rupture, cracking, fatigue, shock, wear, corrosion, misalignment, poor geometrical design and literally hundreds of other factors. Whatever the source, it is important to recognize that it is impossible to separate the product from the process and, as such, material, design and processing applications are all interrelated.

When considering ways to prevent failures from occurring, one determines the factors involved and whether they acted alone or in combination with one another. We ask ourselves questions such as “Which of the various failure classifications were the most important contributors?” and “Was the design robust enough and the safety factors properly chosen to meet the application rigors imposed in service?” Having a solid engineering design, coupled with understanding the application, loading and design requirements, is key to avoiding failures. If failures do happen, we must know what contributed to the damage.

Failure Classifications

There are a multitude of different types of failures and failure classifications, each requiring a detailed analysis of both the external influences and internal influences that contribute to either the success or failure of a product. Failure triangles (Fig. 1) help us visualize these basic classifications and the types of interactions that might take place when failures occur. In most cases, failures happen when one or more of these variables act alone or in combination with one another. These include:

Material Factors: The type and form of material selected for a given application (Table 2) are critical to its performance in a given application.

Design Factors: Fitness for purpose is the principal focus of design (Table 3) and must be innately valid such that the expected service life, service conditions and loading can be safely accommodated.

Processing Factors: Manufacturing practices must be robust and can also contribute to product failures if not properly performed (Table 4).

Heat-Treating Factors: Heat-treatment issues can contribute to failures in a number of ways (Table 5). Caution must be observed to avoid blaming heat treatment for revealing a problem the root cause of which may lie outside the contribution of heat treatment to the condition observed.  

Environmental Factors: Environmental-induced factors (Table 6) can play a significant role in field failures and are one of the most difficult aspects to anticipate or control.

Final Thoughts

Accurate record keeping and careful documentation of failures if/when they occur are of critical importance to assist in determining the root cause of a particular product failure and to avoid its reoccurrence in the future.

More to Come...

Failure triangles and their interactions will be the subject of a future article (Reference 1). Stay tuned. IH