Determination of Compressive Stress Limits for Tightened Plastic Components up to 3 mm in Bolted Joints Applicable in the Automotive Industry

This paper addresses the analysis of compressive stress limit values of plastic components with a thickness of no more than 3 mm used in bolted joints, especially in the automotive industry. The results of the compression tests show that the compressive stress limit values often exceed the tensile stress limit values specified in the material data sheets, which has a significant impact on the way in which reliable bolted joints are designed without the risk of plastic deformation. In addition to compression tests, stress tests involving axial force and torque (combined load typical for bolted joints) were also performed. Th results of both types of tests were compared in the final table, involving a comparison of yield strength under compression and yield strength under a combined load with yield strength and/or stress at break from material data sheets, estimated using tensile stress tests. Various plastic materials were tested, including Acrylonitrile Butadiene Styrene (ABS), Polyamide (PA), Polyoxymethylene (POM), Polypropylen (PP) and the glass fiber-reinforced materials. The tests showed that it is possible to exceed the tensile stress limit in material data sheets by 5 to 10% without plastic deformation and by approximately 50%, in some cases by 280%, when loading by pure compression. Considering the combined load, the compressive stress limit values are within the range of 95 to 224% of tensile stress limits. The results of the study contribute to the optimization of the plastic tightened components design and reduce the need for excessive testing in automotive production.