The cumulative effect of deformation is the gradual accumulation of deformation that occurs over time in a system due to applied loads. It may occur in many materials including metals, concrete, composites, or nonmetals, as well as in structural components, such as pipes and columns. The phenomenon is often caused by long-term static loading, but can also be accelerated by dynamic loading (e.g., during earthquakes).
In metals, the cumulative effect of deformation occurs over time due to applied loads. The basic idea is that we can deform an object if we keep on loading it. This process is known as work hardening and is used in case of forging and cold working of metals. In some cases, such as sheet forming, the deformation may be limited and the total deformation might be only a few percent. On the other hand, work hardening can cause the metal to be so hard that it becomes brittle and susceptible to cracking.
The quantitative effects of cumulative deformation can be described using several parameters, namely strain, strain rate, and yield strength. Strain is the ratio of change in length (deformation) to the original length of the material. The strain rate is a measure of the rate of deformation, which increases with an increase in the magnitude of load. Yield strength is the stress at which a material permanently deforms. As the yield strength decreases, the system becomes more susceptible to deformation.
In structural components such as pipes, columns and beams, the cumulative effect of deformation may occur due to long term static loading or dynamic loading such as during earthquakes. The cumulative effect may cause the collapse of such components.
In concrete, cumulative deformation due to static and dynamic loading may cause cracks and collapse. The phenomenon is usually prevented by using high performance concrete mixtures with higher strengths, low permeability, high shrinkage and creep resistance, and chemical admixtures.
In composites, the cumulative effect of deformation can be accelerated by different factors such as temperature, humidity, ultraviolet radiation, and repeated loading. In addition, creep, fatigue and other phenomena may contribute to cumulative deformation.
In summary, the cumulative effect of deformation is an important phenomenon that can have adverse effects on materials and structures. To prevent it, buildings and structures should be designed, constructed and maintained according to applicable standards. In addition, the effects of different factors such as temperature, humidity, and ultraviolet radiation should be considered in the design process. Furthermore, in the case of long-term static or dynamic loading, preventive measures should be taken, such as using high-performance concrete. Last but not least, the effect of fatigue and creep should be taken into account when designing components that are subjected to repetitive loading.
