MEi Newsletter: 1996 Fall

630·365·9060

Materials Engineering, Inc.

47W605 I.C. Trail

Virgil, IL 60151

	Newsletter



2005 Fall 2003 Spring 2001 Fall 2000 Fall 1999 Fall 1998 Spring 1997 Spring 1996 Fall 1996 Spring 1995 Fall		Of Materials Interest1996 Fall
		Mei Joins the Internet: We're Online! Forensic Engineering: Putting Together the Pieces of a Failure MEi Speaks at Association of Women in the Metal Industries Meeting Unhappy Homecomings: Investigation of Washing Machine Supply Hoses The "What Is It?" Contest
		Mei Joins the Internet: We're Online! MEi is now on the World Wide Web, with its new homepage. You can find us at http://www.flask.com/mei. We are also indexed throughout the web and can be found through search engines and on the ASM International home page of materials related companies. With the debut of our homepage this August, we became the first metallurgical or materials engineering company in Illinois or Wisconsin to be on line. When talking to many of our engineering customers, we found they often search the web looking for information about companies, products and answers to technical questions. We were surprised to find out just how many of our customers are on line. The decision to develop our home page fell naturally out of our desire to provide faster, better service to our customers. Our home page provides information on our capabilities, experience and expertise. It also gives anyone the opportunity to ask us technical questions via e-mail. These questions will then be answered and posted in a section of the page called "Yes Virginia, there is a free lunch." We have always given our customers information and advice on the phone; now this same service is available on line. We feel this level of service differentiates us from other metallurgical and engineering companies. We are committed to assisting you, and we believe that we all benefit from a greater understanding of materials, processing and engineering principles. Visit our site, and e-mail us (mei@flask.com) to let us know what you think! If you have considered putting together a home page, give us a call and we'll tell you about our experiences, and about Flask Productions and designer Dan Wykes, who worked with us putting our home page together. Forensic Engineering: Putting together the pieces of a failure This past summer, the crash investigation of TWA flight 800 and of ValuJet airlines drew the country's attention to the teams of engineers and scientists who are investigating the mystery of why these jets crashed. This field, Forensic Engineering or Failure Analysis, is one of the primary services provided by engineers at MEi. We have many years of experience working on the failures of products, ranging from the space shuttle, to consumer products. The steps followed by the FAA, NTSB and FBI labs are identical to the steps that we follow when we conduct a failure investigation. No matter how big or how small, the same basic thinking process is used to come to the conclusion of what happened and why. A failure investigation can be divided into several steps: Gathering Usage Information: "Looking At The Black Boxes" The most important feature of an investigation is having accurate and inclusive information. The airplane black boxes provide information on exactly what the plane was doing at and just before the time of failure. In our investigation, it is important to know exactly what the product was doing at the time of failure. Gathering Information About The Event: "Interviewing The Witnesses" Eyewitnesses provide the last piece of information as to what was happening as the unit failed. Were there noises or flashes of light? But the information provided by eyewitnesses is not always accurate. This is understandable, as most failures are unexpected, and rarely are people carefully observing the unit looking for signs of distress in anticipation of a failure. Gathering The Evidence: "Sorting Through The Rubble" When a plane crashes, it leaves tons of debris. All the hardware has to be carefully gathered, so that no information is left behind at the sight. The whole picture can be misleading if a critical piece to the puzzle is missing. For our investigations, it is often desirable to look not only at the failed components, but at the entire assembly for signs of distress and supporting evidence. Understanding The Design: "Talking To The Manufacturers" When a plane crashes, the investigation team always includes technical representatives from the companies that manufacture the airplane, the engines and key subsystems. The investigation is conducted by a team. We consider your technical staff to be a key part of our failure investigation team, providing us with information about the design, design changes, failure history and performance expectations. While as engineers, we have a good understanding of how systems operate, the details that your staff provide on the unique features of the product are often invaluable to us in getting the job done efficiently. Macroscopic Examination Of The Hardware: "Deciding What And Where To Examine" Just as the NTSB does not microscopically examine every inch of the failed aircraft, it is not a wise use of resources to start with a detailed examination of large components. We always begin with a macroscopic examination of the components at magnifications up to 90x using optical microscopes. Our experience allows us to sort the wheat from the chaff, and to determine which areas will provide the most information through detailed analysis. Detailed Scientific Examination Of The Hardware: "Sending It Back To The Lab" We use the same tools that the NTSB labs use to determine the cause of failure. The scanning electron microscope (SEM) is the key instrument. In fact, many in the forensic engineering field divide the history of failure analysis into two eras: before the invention of the SEM and after the invention of the SEM. Other techniques, such as metallographic examination, chemical analysis and mechanical testing also provide key information. Defining The Failure Mode: "Determining The Cause" From macroscopic and microscopic examination, the failure mode can be determined. This, coupled with understanding of the design and information about what was happening at the time of failure, allows a failure scenario to be developed, which proposes exactly what happened during the failure. Making Sure All The Pieces Fit: "Tracking Loose Ends" Once a failure scenario is defined, all the hardware and information must be re-examined to insure that all the pieces support the failure sequence. Cause and effect logic must be carefully thought through to insure no evidence contradicts the proposed failure scenario. If the pieces don't fit, it's time to rethink and gather more information. Dissemination Of The Information: "Press Conference" Just as the NTSB will call a press conference once they have an understanding of the failure, we will call you and let you know our findings. We will discuss all the findings to insure you clearly understand the failure scenario, and to further verify all the pieces fit. Defining And Implementing Corrective Action: "Making Sure It Doesn't Happen Again" We all want to be perfectly safe when we fly. We want what ever happened to the ValuJet or TWA planes to be prevented on all future flights. Likewise, we want your products to offer high performance and long life in the marketplace. We will work with you to determine what can be done from a design, materials or usage viewpoint to insure safety and reliability in your product. Sometimes this is just a simple suggestion, other times it involves complex analysis. Our experience in product design and understanding of failure scenarios makes us a valuable member of your team to prevent future failures. Materials Engineering Inc. has many years of failure analysis experience. Let us work with you to help you solve your "plane crashes". MEi Speaks at Association of Women in the Metal Industries Meeting MEi President and Principal Engineer Bill Durako addressed the Rockford chapter of the Association of Women in the Metal Industries (AWMI) at their July dinner meeting. As the name suggests, this is an organization is of women whose jobs or companies are in the metal industries. They are a dynamic and diverse organization with membership ranging from engineers and manufacturing staff to purchasing agents and marketing representatives. The topic was "How Hardness and Ductility Affect Manufacturing and Processing" giving a general overview of how and why ductility or formability and hardness or strength must be considered to insure a component is both manufacturable and of sufficient strength for the application. The talk included a discussion on the principles of heat treatment and of basic forming processes. Also speaking at the meeting was Dave Voss of Voss Metals, who discussed the importance of chemistry in metals and alloys for recycling. If you would like one of our engineers to speak at your company or technical society, please give us a call. If you are interested in learning more about AWMI, please contact Sue Lackner of W.A. Whitney at 815-964-6771. Unhappy Homecomings: Investigation of Washing Machine Supply Hoses Every year, a large number of washing machine supply hoses fail, allowing water to flood into homes and cause large amounts of water damage. MEi recently completed an investigation of washing machine hose materials for a major insurance company. As most of us have washing machines at home, we thought that sharing these results with you might help to prevent a failure in your home, and save you the trouble of water damage. The Failure Investigation: MEi began by looking at a series of failed hoses from insurance claims. Insurance investigators had noticed a pattern. The failures were occurring in the rubber hose portion adjacent to the metal end coupling. Corrosion was often found in the fitting. The failures were occurring only in the hot water supply hose and not in the cold water supply hose. Information appeared to indicate that certain hose manufacturers had a greater incidence of failure. All standard hoses are manufactured from isoprene, or natural rubber, with fillers and reinforcing fabric added. The Cause: Through optical, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and other analytical techniques, it was determined the failures were a result of a combination of three factors: Chlorine in the water attacks (oxidizes) the rubber polymer. This fact has been known for years: in the presence of chlorinated water, rubber will degrade given enough time. Municipal water supplies contain up to 3.5 ppm of chlorine. Elevated temperature accelerates the attack. The oxidation reaction is kinetic, and the attack becomes more aggressive as temperature increases. Many hot water heaters operate at 150°F, nearing the maximum usage temperature for natural rubber of around 170°F. Bends in the hose accelerate the attack. When a hose is bent, the polymer chain is subject to a tensile load, resulting in stress on the polymer. Stressed polymers are more susceptible to chemical degradation than unstressed polymers. Therefore, hot water supply hoses that are bent or kinked (by pushing the machine against the wall) will degrade and fail given sufficient time. Materials Testing: Accelerated testing conducted on sections of hoses both stretched and unstretched from four different materials/hose suppliers in chlorinated 150(F water was able to recreate damage to the rubber, and thus verify the failure mode. Test results did show differences between brands of hoses, and types of rubber. The less expensive natural rubber hoses were the most susceptible to damage. But surprisingly, even the better materials such as EPDM and PVC still showed some evidence of degradation. Prevention: While it is statistically unlikely that you will experience a hose failure and resulting water damage, there are several simple steps that you can follow to help prevent a hose failure and water damage to your home: If you can't remember the last time you changed hoses, it has been too long. Make sure there are no sharp bends or kinks in your hose. Pull the machine away from the wall a few more inches to eliminate bends. Hoses with 90∞ elbows in the metal end fittings are useful in preventing bends or kinks. Turn down the water heater a few degrees. When buying hoses, spend a few extra dollars for better hoses. Even the most expensive hoses are less than $15. While we cannot recommend a particular brand, the less expensive natural rubber hoses did offer the least resistance to damage of all the hoses tested. You might also check with your local appliance parts store, as they may have experience and opinions on which hoses offer superior performance. Washing machine manufacturers have additional recommendations, found in the owners manual which most of us never read. Change hoses a minimum of every 5 years. Turn off the water supply to the hoses when not using for long periods of time, especially when you are on vacation. Remember, only YOU can prevent hose failures. The "What Is It?" Contest The scanning electron microscope (SEM) is a powerful tool, capable of magnifications up to 180,000 times. It allows us to reveal information which is critical to metallurgical investigations, such as fracture modes and surface characteristics. The SEM can also be fun to play with, because it allows one to view the surface of anything at high magnification with great depth of field. All of us have been amazed by the pictures of various insect parts, especially the eye of a fly. In our contest, we take a look at an object on the SEM that should be familiar to all of you, and ask you to identify it. This issue, we show you two very similar objects, and ask you What are they? How do they differ? As this should be an easy one, no clues will be given this time. 330X330X Please fax us or e mail us (don't call) with your answer. We will draw a winner from all correct entries received by October 30. The correct answer and the winner will be published in the next issue Of Materials Interest. The prize is a $50 restaurant gift certificate, so put on your thinking caps.
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