What are the factors that cause plastic products to fail?

1, material selection

In plastics or other industries, failures that result from hasty selection of materials are not uncommon. In applications where high impact resistance is required, high impact materials must be specified. If the material needs to be used outdoors for a long time, an anti-UV material must be specified. In order to choose the right material, careful planning, a comprehensive understanding of the plastic, and reasonable prototype testing are required. The choice of materials should not be based solely on cost.

In order to select the best material for any application, a systematic approach to the material selection process is required. Suitable material selection techniques involve carefully defining the requirements of the application in terms of mechanical, thermal, environmental, electrical, and chemical properties. In many cases, it makes sense to design thin-walled products with the advantages of hardness and weight ratio of engineering materials with high priced and fast cycle times. Many companies, including material suppliers, have developed software to assist in the selection of materials simply by selecting the application order of importance.

2, design

A single material selection does not prevent material failure. When designing a plastic product, the designer must design a special part using the basic rules and guidelines provided by the material supplier for that material. It must be remembered that in addition to the basic rules of designing a few plastic parts, the design criteria from one material to another and from one application to another will change. Today, design-related failures are by far the most common type of failure. The importance of a large enough rounded corner cannot be overemphasized. The figure below shows how the stress concentration factor increases significantly as the fillet radius/thickness ratio decreases.

3, processing technology

After proper material selection and design, responsibility is transferred from the designer to the plastics processing staff. The most innovative designs and very careful material selections do not compensate for the poor product forming process. Forming internal stresses, shrinkage cavities, weak weld lines, and moisture in the material are the most common causes of premature failure of some products. Recent developments in process control technology allow process personnel to control the process with a high degree of reliability and also help to maintain a record of a product that may fail in the future. The recording of these molding processes is invaluable for failure analysis of a person. Any assembly or secondary operation of the molded product must be carefully evaluated to avoid premature failure. Failures caused by stress cracking, drilling and welding around the metal insert are common.

4, the conditions of use

Despite the built-in safety factor warning labels and user guides, failures due to usage conditions are common in the plastics industry. The following are five types of unintended use conditions:

Appropriate abuse;

Use products that exceed their life expectancy;

Product failure due to unstable conditions of use;

Product failure due to conditions beyond the appropriate abuse;

Synergistic effect of simultaneous application of both stresses.

Most of the stress imposed on plastic products in use can be classified under the headings of thermal, chemical, physical, biological, mechanical, and electrical.

Type of failure:

Mechanical failure

Mechanical failures are caused by the application of external forces, which cause deformation, cracking, or breakage of the product into pieces when they exceed the yield strength of the material. This force may be the tensile, compressive, and impact forces of short or long term forces applied under different temperature and humidity conditions.

Thermal failure

Thermal failure occurs when the product is exposed to extreme heat or cold. At unusually high temperatures, the product may warp, twist, melt or even burn. At low temperatures, the product tends to become brittle, even the slightest load can cause cracking or even damage to the product.