The ability of a product to last for a longer period of time, right from its first use till its discarding, is what reflects the sustainability and integrity of the manufacturing organizations. To be a market leader, designing products that lasts is what the end consumer expects; and to achieve this, manufacturers must adopt cutting-edge technology and engineering knowledge at its paramount level.
Additionally, for the sake of environment concerns, regulatory authorities already force manufacturers to develop products that not only have longer life but also possess the ability to be recycled.
From an engineering point of view, longer lasting products directly points to a phenomenon called “Fatigue”, which in simpler terms is nothing but a weakening of the material due to repeatedly applied loads. It is quite obvious for a product to fail when the amount of stress and load bearing capacity exceeds the permissible value.
However, failures due to fatigue occur even when the stresses are below the limiting value. This unexpected failure is due to the less harmful but repeated loads applied in cyclic applications. It is not surprising from the NBS report which states that 80-90% of all structural failures occur through fatigue mechanism, costing manufacturers more than $600B per year.
It is evident that fatigue phenomenon is dependent on design, material properties and loading conditions. In order to assess the fatigue damage, two fundamental methods are utilized in general: the stress-life (S-N) method and the strain-life (E-N) method.
The SN method uses stress curves derived from tests on samples of the material to be characterized and also calculates number of cycles to failure. The EN method on the other hand utilizes strain life relation equation to determine strain cycles leading to crack initiation in the material sample.
Evaluating the product design for fatigue life using any of the two methods provides benefits of predicting the product life, compared to designs developed using conservative approach. However, experimental assessment is often costly and time consuming, causing significant loss in time-to-market the product.
To compensate this problem, computer aided engineering techniques such as finite element analysis shall be utilized. Modern FEA solvers are capable to perform fatigue analysis using either of the two approaches. Additionally, it is also possible to optimize the design before the fabrication stage, reducing the manufacturing time significantly.
Fatigue analysis of a product also provides the ability to forecast the product performance in the market and establishing the warranties. Predicting the useful life of the product brings confidence in the design team and helps bring innovation in the design process, allowing manufacturers to establish themselves as market leaders.