Search Results for distortion

Distortion failure occurs when a structure or component is deformed so that it can no longer support the load it was intended to carry. Every structure has a load limit beyond which it is considered unsafe or unreliable. Estimation of load limits is an important aspect of design and is commonly computed by classical design or limit analysis. This article discusses the common aspects of failure by distortion with suitable examples. Analysis of a distortion failure often must be thorough and rigorous to determine the root cause of failure and to specify proper corrective action. The article summarizes the general process of distortion failure analysis. It also discusses three types of distortion failures that provide useful insights into the problems of analyzing unusual mechanisms of distortion. These include elastic distortion, ratcheting, and inelastic cyclic buckling.

Distortion often is observed in the analysis of other types of failures, and consideration of the distortion can be an important part of the analysis. This article first considers that true distortion occurs when it was unexpected and in which the distortion is associated with a functional failure. Then, a more general consideration of distortion in failure analysis is introduced. Several common aspects of failure by distortion are discussed and suitable examples of distortion failures are presented for illustration. The article provides information on methods to compute load limits, errors in the specification of the material, and faulty process and their corrective measures to meet specifications. It discusses the general process of material failure analysis and special types of distortion and deformation failure.

An experimental high-temperature rotary valve was found stuck due to growth and distortion after approximately 100 h. Gas temperatures were suspected to have been high due to overfueled conditions. Both the rotor and housing in which it was stuck were annealed ferritic ductile iron similar to ASTM A395. Visual examination of the rotor revealed unusually heavy oxidation and thermal fatigue cracking along the edge of the gas passage. Material properties, including microstructure, composition, and hardness, of both the rotor and housing were evaluated to determine the cause of failure. The microstructure of the rotor was examined in three regions. The shaft material, the heavy section next to the gas passage and the thin edge of the rotor adjacent to the gas passage. The excessive gas temperatures were responsible for the expansion and distortion that prevented rotation of the rotor. Actual operating temperatures exceeded those intended for this application. The presence of transformation products in the brake-rotor edge indicated that the lower critical temperature had been exceeded during operation.

The engine of an automobile lost power and compression and emitted an uneven exhaust sound after several thousand miles of operation. When the engine was dismantled, it was found that the outer spring on one of the exhaust valves was too short to function properly. The short steel spring and an outer spring (both of patented and drawn high-carbon steel wire) taken from another cylinder in the same engine were examined in the laboratory to determine why one had distorted and the other had not. Investigation (visual inspection, microstructure examination, and hardness testing) supported the conclusion that the engine malfunctioned because one of the exhaust-valve springs had taken a 25% set in service. Relaxation in the spring material occurred because of the combined effect of improper microstructure (proeutectoid ferrite) plus a relatively high operating temperature. Recommendations included using quenched-and-tempered steel instead of patented and cold-drawn steel or using a more expensive chromium-vanadium alloy steel instead of plain carbon steel; the chromium-vanadium steel would also need to be quenched and tempered.