Plastics part failure is generally related to one of four key factors including Material Selection, Design, Process and Service Conditions.
Types of Failure
Mechanical Failure
Mechanical failure arises from the applied external forces which, when they exceed the yield strength of the material cause the product to deform, crack, or break into pieces. The force may have been applied in tension, compression, and impact for a short or a long period of time at varying temperatures and humidity conditions.
Thermal Failure
Thermal failures occur from exposing products to an extremely hot or extremely cold environment. At abnormally high temperatures the product may warp, twist, melt, or even burn. Plastics tend to get brittle at low temperatures. Even the slightest amount of load may cause the product to crack or even shatter
Chemical Failure
Very few plastics are totally impervious to all chemicals. Chemical failure occurring from exposing the products to certain chemicals is quite common. Residual or molded-in stress, high temperatures, and external loading tend to aggravate the problem.
Environmental Failure
Plastics exposed to outdoor environments are susceptible to many types of detrimental factors or environmental failure. Ultraviolet rays, humidity, microorganisms, ozone, heat, and pollution are major environmental factors that seriously affect plastics. The effect can be anywhere from a mere loss of color, slight crazing and cracking, to a complete breakdown of the polymer structure.
Analyzing Failures
The first step in analyzing any type of failure is to determine the cause of the failure. Before proceeding with any elaborate tests, some basic information regarding the product must be gathered. If the product is returned from the field, have the district manager or consumer give you basic information, such as the date of purchase, date of installation, date when the first failure encountered, geographic location, types of chemicals used with or around the product, whether the product was used indoors or outdoors. All this information is very vital if one is to analyze the defective product proficiently. For example, if the report from the field and the defective product indicate a certain type of chemical was used with the product, one can easily check the chemical compatibility of the product or go one step further and simulate the actual use condition using the same chemical. Recordkeeping also simplifies the task of failure analysis. A simple date code or cavity identification number will certainly enhance the traceability. Many types and styles of checklists to help analyze the failures have been developed. Seven basic methods are employed to analyze product failure.