Kappa Multistation for Plastics
Durability is a term used in materials science, which refers to the calculated service life of a component. Durability describes the ability of materials and components to withstand static, quasi-static and dynamic (recurring or impact) loads without damage, within the calculated service life and under consideration of relevant environmental conditions. Methods for durability determination can be either calculated methods or test results. It is a cross-sectional science consisting of the interaction of load (mechanical and environmental), material, production and construction.
Dynamic stresses are almost invariably the cause of component failure. Often the failure occurs with loads that are significantly below the failure load observed in static tensile tests. The fatigue life, as part of the durability, designates the deformation and failure behavior of materials under cyclic stress.
The number of cycles that a component can withstand under operating load until failure can be predicted with statistical accuracy using the S-N curve.
Many times developers do not design a component to be fatigue resistant, but rather to exhibit high durability.
For determination of the durability of a component, all types of loading must be considered—from static creep loading to impact loading to cyclic loading, at constant or variable amplitude. Environmental conditions such as temperature, precipitation, pressure, as well as changes in the material due to corrosion or aging are taken into consideration. The challenge then is to determine characteristic values using the simplest possible tests, on the basis of which the designer can develop a reliable component.
The problem here is that the damage process is highly complex and cannot actually be described by a single parameter. It always begins with the formation of micro-cracks emanating from internal flaws or notches at which cyclic plastic deformations occur. The LCF test is used in the attempt to describe this process. This is followed by crack growth up to failure, for which the methods of fracture mechanics are used.
The high cycle fatigue test (also S-N test) makes no distinction between crack initiation and crack growth. Using the S-N curve, it is relatively easy to predict service life at variable loading amplitudes by means of damage accumulation methods (e.g. Plamgren/Miner).
However, there is still the component test for verification, although this involves significantly less effort thanks to modern methods of material characterization.
Today, durability is tested in almost all technical fields. Durability offers certain advantages, particularly in lightweight construction. Components require less material and therefore have a lower mass when they are designed to be durable rather than fatigue resistant. In the automotive industry, for example, a lighter vehicle requires less fuel, but the lighter structure also allows a higher load capacity. Durable design in part also fulfills a functional requirement: airplanes designed to be fatigue resistant would not be able to fly since they would simply be too heavy.
During its operation, almost every component of a machine, system or vehicle is exposed to mechanical loads that cause change over time. The task for developers is to create a product that fulfills its function over its entire service life. This is often contrasted by short development times, demands for lightweight construction and cost-effective production. The application of calculated service life estimation in fatigue testing supports the reliable and economical design of components. Fatigue fracture mechanics additionally supports the description of crack growth. Characteristic numbers from the non-destructive test can be included in product development.
The goal for a durable component is