The Failure of Metal Parts – A Case Development Guide for Lawyers

During World War II, more than 250 liberty ships cracked open for no apparent reason. Nineteen of them broke completely in half.  The study of these disasters led to the development of the science now known as fracture mechanics. Among other phenomena revealed by these studies was the fact that large pieces of metal such as I-beams and plate steel can spontaneously burst apart due to internal “residual” stresses both before and after they are welded, bolted or riveted into more complex structures. The energy necessary to burst one of these objects apart is equivalent to the energy required to put it back together. It was a shocking discovery that such energy could be pent up in a seemingly inert piece of metal.

Despite advances in material science from the study of the liberty ships, major disasters have continued to occur. In 1967, forty-six people died when the Silver Bridge in West Virginia collapsed, plunging their cars into the Ohio River.  In 1981, two “sky bridge” walkways in a one year old Kansas City hotel lobby collapsed, killing 45 and injuring 150.  This past summer, a roof panel in a Big Dig tunnel in Boston fell, killing an unlucky automobile passenger.  While most of us will never have to deal with cases with such high profiles, the failure of metal parts is not uncommon, and personal injury lawyers in Maine should understand how to approach them. Only a good investigation can lead to a good result.

Why Metal Parts Fail

Metal parts fail for a few basic reasons:

  1. trouble with the material;
  2. inadequate product design;
  3. manufacturing or assembly faults;
  4. environmental degradation; and
  5. mis-use or abuse.

In most cases, two or more of these problems combine to cause failure, which may be in the form of bending, buckling or breaking.  The challenge for the plaintiff’s lawyer is to identify which of the factors are most important, and whether any of the evidence will support a liability argument that will help the client.

Gather and Protect the Pieces

Understanding and explaining metal failure always begins with attempting to locate the place where the failure began.  Starting with as many broken fragments as possible, investigators will test the material itself to see whether the correct type of metal was specified for the job, whether its chemistry is as expected, and whether it was properly heat-treated for its intended use.  They will examine the exterior surfaces for witness marks, tool marks, corrosion, repair and cracking, and check for signs of bending, buckling, twisting or other instability. On fracture surfaces, they will look for old rust, evidence of the direction of crack propagation, signs as to whether a single  crack developed in one spot and spread outward, or whether a web of many simultaneously-developing cracks joined together to trigger the failure. They will look to see whether failure occurred incrementally over time or whether there was a sudden catastrophic event from the application of a single load.

Because all of the analysis described above depends on the condition of the broken parts, care must be taken to collect as many pieces as possible, and to protect them from further damage. Pieces should be marked in a non-destructive way, and kept dry. No effort should be made to straighten or wiggle bent parts. Careless packaging or repositioning of the  mating pieces of a fracture can damage the microscopic evidence on the fracture surface, so it is never appropriate to touch the fracture faces together, or even touch them with one’s hands.

Obtain Exemplars

If the metal part that failed was a component of a common product which is not too expensive, it may be possible to obtain new exemplar products.  That includes items which are identical in design to the failed item, as well as similar products from other manufacturers.  It may also be possible to order replacement parts to learn whether components have been redesigned or strengthened.  Studying the alternative designs can help explain what went wrong in the case at hand, and the exemplars can be used as demonstrative aids or for testing.

Find Other Similar Incidents

Evidence of other similar incidents may be used in a product liability case to show notice of the defect, to support causation arguments, and to support punitive damage claims.  Aside from looking in databases maintained by third parties and in the defendant’s own business records, you may find evidence of similar failures close at hand.  On a vehicle with four wheels, the left and right sides may be mirror images.  If one side fails, look on the other side to see how the component parts are holding up. Looking at used products of the same make and model can also be helpful.

Locate Expert Witnesses

Expert witnesses will ultimately be required to explain the failure of metal parts. Both a design engineer and a metallurgist may be required.  However, do not overlook the value of a local mechanic, repairman, or service manager.  These individuals may not ultimately testify, but they are invaluable sources of insight and common sense.

Aside from assessing the metallurgical aspects of the evidence, experts can help put the case in perspective by explaining how the failed part was intended to work. Although most metal is considered to be a hard substance, all metal has an elastic range or a capacity to change shape and then return to original form. In that sense, almost all metal parts are really springs which constantly move with changes in temperature and with applied forces. Thinking about metal parts in this way is necessary to understanding the product’s design, how its construction and assembly may have contributed to failure and whether mis-use may be a problem in the case.

Stay In Control

Regardless of what stage a case investigation is in, an attorney should never give up personal responsibility for or control of the evidence, both physical and testimonial.  From the client’s first description of what happened to the expert’s suggestion about how and when the analysis should be done, it is necessary and appropriate to raise challenging questions.  In a case involving a steel wrench with no moving parts, the client may say that he was simply attempting to remove a nut from a rusty bolt when the wrench broke.  The pieces flew apart and he lost two teeth. For that to be true, the wrench would have to come apart in a counter-clockwise direction.  If expert metallurgic analysis of the failure surfaces reveals that the wrench came apart while moving clockwise, what is the explanation for this contradiction? Is the scientific evidence wrong, or is the client’s story wrong? In a case like this, the client would probably not be telling the whole truth about what happened.  While it may have been true that he was attempting to remove the nut from the rusted bolt, his chosen method may have been to over-tighten the nut clockwise in an effort to simply snap off the rusted bolt.  Is that product misuse or abuse?  Such a problem would be easier to deal with if the client were to tell his lawyer the whole story before his deposition rather than after.

A turbine in a paper mill flies apart, and the mill workers all proclaim their surprise.  Metallurgic analysis reveals no flaws in the base metal, no design, construction, or environmental reason why the metal should have flown apart.  Close questioning reveals that the mill workers had disabled an over-speed trip device in order to keep the machine up and running.  The earlier in the case that these facts are known to the plaintiff’s lawyer, the better. No lawyer can make a witness tell the truth, but we must always be vigilant and slightly skeptical. We must ask that our experts rigorously scrutinize the evidence, and be sure that all witnesses avoid telling us only what we want to hear.

One way to be in a position to ask good questions is to buy a textbook or other source material on the subject at hand. While some technical reading requires a sophisticated science background, most introductory chapters are readable to someone who is curious.

Additional control issues arise over possession of the broken parts and destructive testing. If the plaintiff does not own the failed parts, he should try to make a deal with the employer, worker’s compensation carrier, or whoever else is involved to secure and protect the evidence. If an adverse party has the evidence, plaintiff should make a written request to inspect and photograph it, and expressly ask that no destructive changes be made. If the plaintiff possesses or controls the evidence, he should not mail or ship it off to anyone.  No good can come from having crucial evidence in transit or unsecured. In a serious injury case, defendants and their insurers are always willing to travel to make their own inspection.

The risks of destructive testing are obvious. Once the parts are altered, they can never be restored to their immediate post-failure condition. Heat from cutting, grinding or drilling can be enough to change important features of the parts, so even taking samples from ladders and other large items should be done with extreme caution. Generally, no destructive testing should be carried out without the presence of all interested parties, and then the testing should be done pursuant to an agreed-upon written protocol.


It is never easy to get a case from the first client interview to a successful resolution. It can be particularly hard in a case involving metal failure, where the procedures for investigating the case are unfamiliar and the issues are technical. By imposing discipline and focus on the process from beginning to end, attorneys will give their clients the best chance for a good outcome.