banner ad
Experts Logo

articles

Elements of Failure Analysis

By: Wayne Reitz, PhD, PE
Tel: 701-235-0859 - Fax: 701-235-6122
Email: Email Dr. Reitz
Website: www.reitzmetallurgy.com

Profile on Experts.com.

Abstract

Failure analysis is conducted to determine the root cause of failure. Sometimes these failures are catastrophic, e.g., Titanic. Other times the failures are a nuisance, e.g., failed o-ring in plastic faucet water valve. In both cases, the component failed unexpectedly, which can result in injury or death, not to mention financial loss due to unscheduled downtime. By using the information presented in the failed component a company could reduce, or eliminate, the possibility of re-occurrence of that type failure. This paper will discuss failure analysis in general terms and provide several case studies. The areas of failure analysis to be presented include typical tools, steps in conducting a failure analysis, theory of crack propagation, typical failure mechanisms, and case studies.

Introduction

It may sound like a bad joke, but what do manufacturers, insurance companies, and lawyers have in common? From an engineering viewpoint the common factor is providing engineering analysis to determine the root cause of why a component failed. Manufacturing companies want to save money, be more efficient, reduce down-time, and have proper preventive maintenance programs. Insurance companies do not want to pay a claim if abuse of the equipment was responsible for the failure and resulting claim. Lawyers need engineering data to assist in proving their case.

Failure analysis is a broad discipline that includes metallurgy and mechanical engineering. Some personal attributes of a good failure analyst include common sense, the willingness to expect the unexpected, and of course, a strong understanding of the engineering theory. Some of the typical tools include various forms of examination, e.g., visual and electronic. There are numerous steps in completing a failure analysis study and they should be performed in the proper sequence.

This paper introduces the above concepts and provides a few case studies showing how engineering knowledge and the ability to apply it work in these problem solving scenarios.

Typical Tools
Failure analysis provides insight into failure mechanisms if the analysis is thorough and accurate and all the necessary tests are performed. If the analysis is incomplete, then the wrong conclusions will be reached with possible serious future consequences. This paper only addresses a few of the tools, but they are all inter-related. There are several references the reader can obtain to become familiar with all the possible tools available.(1, 2, 3, 4)

Visual exam
The overall condition of the component is quite important, beyond just looking at the fracture surface. It is important to determine the exposure of the entire component to the environment, which includes temperature, acid, tensile or compressive stresses, impact forces, corrosion, and wear. Just receiving a portion of the failed component, i.e., the fractured surfaces will not allow a fully justifiable conclusion to be determined. The author experienced this very concept a few years ago, which made the investigation quite challenging.(5)

Macroscopic exam
The initial view of the fractured surface provides many clues that will aid the failure analyst in determining the responsible failure mechanism. The presence of oxide on a portion of the fracture surface indicates a long exposure to the atmosphere, a smooth surface could indicate rubbing of the mating surfaces after fracture. Certain features will assist the failure analyst in where to concentrate the area of evaluation, e.g., ratchet marks and beach marks. There are several excellent references that can aid the reader. (1, 6, 7)

. . . Continue to article and footnotes (PDF).


Wayne Reitz, Phd, PE, performs metallurgical evaluations, mechanical testing, failure analysis, and forensic metallurgy for industry, insurance claims, and as expert testimony.

See Dr. Reitz's Profile on Experts.com.

©Copyright 2000-2007 - All Rights Reserved

DO NOT REPRODUCE WITHOUT WRITTEN PERMISSION BY AUTHOR.

Related articles

Mechanical-Safety-Engineering-Logo.gif

2/26/2014· Failure Analysis

Forensic Clues: Elderly Mobility Aids

By: John Ryan, BSME, PE

A significant number of elderly persons experience falls every year. In 2010, 2.3 million nonfatal fall injuries involving elderly people were treated in emergency rooms around the country. In the same year, 21,700 elderly people died as the result of unintentional falls. Falls for elderly people are extremely hazardous as they may not recover from fractures and other injuries.

Mechanical-Safety-Engineering-Logo.gif

9/26/2013· Failure Analysis

Forensic Clues: Seat Belt Failure

By: John Ryan, BSME, PE

In 2007, an estimated 15,147 lives were saved from seat belt use. Seat belts save five times more lives than airbags, according to statistics released by NHTSA. Seat belt use has increased over the years, due to cultural trends, and possibly due to the enactment of seat belt use laws. Seat belt systems do not always function as predicted. Seat belt systems can fail during a collision, often resulting in serious injury or death to the vehicle occupant.

thomas_read_photo.jpg

8/7/2012· Failure Analysis

Failure Analysis: Metal Fatigue of Automatic Machinery - Wafer Test Station

By: Dr. Thomas Read

During normal operation, the arm on an automatic wafer test station failed. Root cause failure analysis determined that the drive shaft on the right angle gear motor used to raise and lower the manipulator arm had failed first.

;
Experts.com-No broker Movie Ad

Follow us

linkedin logo youtube logo rss feed logo
;