Question

How can engineers help avoid catastrophes such as the Jonestown flood, Chernobyl, the Tacoma Narrows Bridge, the Kansas City hotel walkway, Challenger and Colombia? Are there any common root causes for these events? Can you plan for failure? Can you learn from failure?

Answer 1

HOW CAN ENGINEER HELP

In the field of engineering, the importance of safety is emphasized. Learning from past engineering failures and infamous disasters such as the Challenger explosion brings the sense of reality to what can happen when appropriate safety precautions are not taken. Safety tests such as tensile testing, finite element analysis (FEA), and failure theories help provide information to design engineers about what maximum forces and stresses can be applied to a certain region of a design. These precautionary measures help prevent failures due to overloading and deformation.

COMMON ROOT CAUSES

Failure due to static loading

  Static loading is when a force is applied slowly to an object or structure. Static load tests such as tensile testing, bending tests, and torsion tests help determine the maximum loads that a design can withstand without permanent deformation or failure. Tensile testing is common when calculating a stress-strain curve which can determine the yield strength and ultimate strength of a specific test specimen.The specimen is stretched slowly in tension until it breaks, while the load and the distance across the gauge length are continuously monitored. A sample subjected to a tensile test can typically withstand stresses higher than its yield stress without breaking. At a certain point, however, the sample will break into two pieces. This happens because the microscopic cracks that resulted from yielding will spread to large scales. The stress at the point of complete breakage is called a material’s ultimate tensile strength.

Failure due to fatigue

In mechanical design, most failures are due to time-varying, or dynamic, loads that are applied to a system. This phenomenon is known as fatigue failure. Fatigue is known as the weakness in a material due to variations of stress that are repeatedly applied to said material.[8] For example, when stretching a rubber band to a certain length without breaking it (i.e. not surpassing the yield stress of the rubber band) the rubber band will return to its original form after release; however, repeatedly stretching the rubber band with the same amount of force thousands of times would create micro-cracks in the band which would lead to the rubber band being snapped. The same principle is applied to mechanical materials such as metals.

Failure due to miscommunication

  If engineers do not adequately communicate among one another, a potential design could have flaws and be unsafe for consumer purchase. Engineering disasters can be a result of such miscommunication. Such disasters include the 2005 levee failures in Greater New Orleans, Louisiana during Hurricane Katrina, the Space Shuttle Columbia disaster, and the Hyatt Regency walkway collapse.

Failure due to software

  Engineering products and inventions are utilized everyday including computers, microwaves, and elevators. A broken microwave can have limited consequences; however, when larger projects such as infrastructures and airplanes fail, multiple people can be affected which leads to an engineering disaster.

PLAN FOR FAILURE

• The first is that the structure is not strong and tough enough to support the load, due to either its size, shape, or choice of material. If the structure or component is not strong enough, catastrophic failure can occur when the structure is stressed beyond its critical stress level.
• The second type of failure is from fatigue or corrosion, caused by instability in the structure’s geometry, design or material properties. These failures usually begin when cracks form at stress points, such as squared corners or bolt holes too close to the material's edge. These cracks grow as the material is repeatedly stressed and unloaded (cyclic loading), eventually reaching a critical length and causing the structure to suddenly fail under normal loading conditions.
• The third type of failure is caused by manufacturing errors, including improper selection of materials, incorrect sizing, improper heat treating, failing to adhere to the design, or shoddy workmanship. This type of failure can occur at any time and is usually unpredictable.
• The fourth type of failure is from the use of defective materials. This type of failure is also unpredictable, since the material may have been improperly manufactured or damaged from prior use.
• The fifth cause of failure is from lack of consideration of unexpected problems. This type of failure can be caused by events such as vandalism, sabotage, or natural disasters. It can also occur if those who use and maintain the construction are not properly trained and over stress the structure.

LEARN FROM FAILURE

As students attempt to build their own structures or inventions, they will begin to see that their first design rarely works. It is the process of design, testing, failure, and redesign that leads to innovation. When we consider the large number of engineering endeavors undertaken, it is incredible how few failures actually occur. This is because tedious planning and testing behind the scenes prevent most potential failures.

Building models is an important aspect of predicting and avoiding problems that might occur with full-scale applications. Models are generally smaller, more quickly built, less-expensive versions of the final project. Modern engineering methods rely on computational models to predict the stress on and resilience of various materials and designs. Specialized software can generate 3-D computer models that engineers can manipulate to test simulations without ever building a tangible object. Some elements of these methods were the result of analyzing past engineering failures.

This engineering disaster has become 1 of the most studied examples of structural design failure. Physics, mathematics, and engineering professionals and students alike applied their knowledge of forces and aerodynamics to evaluate what went wrong. Forced resonance from the continuous wind often receives blame for the failure, but further studies point to a phenomenon called aeroelastic flutter. Due to the bridge's solid sides and narrow length, the wind could violently vibrate the structure. The vibration, acting in a kind of positive feedback for itself, escalated to dangerous levels. The lessons from this failure have influenced the design of the great suspension bridges built since. Modern suspension decks are wider and of greater mass to reduce vibrations, and these decks also have an open design so that wind can pass through.

Discussing engineering disasters with your students might ignite their interest in design, innovation, and problem solving. If nothing else, it will highlight human perseverance and the tendency of engineers to develop better, safer structures in the wake of failure. When students understand how many trials it takes professionals to create a working model, they may be more willing to keep trying after their first brush with failure.