A cyclic load in a closed cycle is a repetitive mechanical load that causes the accumulation of micro-damage and leads to fatigue failure of structures. It arises from periodic changes in the operating modes of systems; it is taken into account during design, assessed using fatigue curves, and its adverse effects are mitigated through the selection of materials, structural optimisation and monitoring.
A cyclic load in a closed-loop system is a repetitive mechanical load that acts cyclically on the components of mechanisms and structures, leading to a gradual accumulation of damage and potential fatigue failure under prolonged exposure, which is a key factor determining the service life of closed-loop systems for various applications.
A cyclic load in a closed-loop system arises from periodic changes in the operating modes of system components, such as the rotation of shafts, the reciprocating motion of assemblies, and cyclic changes in pressure within hydraulic or pneumatic circuits. Each complete cycle of change in the magnitude and direction of the force leaves microscopic traces of deformation in the material’s structure, which do not disappear when the load returns to its initial value.
The gradual accumulation of microdeformations under the action of a repetitive cyclic load leads to the formation and growth of fatigue cracks, which over time may reach a critical size and cause sudden failure of the component even at a load level well below the material’s tensile strength under static loading. This effect is particularly dangerous for closed-cycle systems, where the load varies at a constant frequency throughout the entire service life.
To assess the effect of cyclic loading, engineers use standard fatigue curves, which relate the load amplitude, the number of cycles to failure and the material properties of the component. Modern numerical models also allow the simulation of damage accumulation in closed-loop dynamics, taking into account real-world operating conditions and possible deviations of load parameters from their nominal values.
The negative impact of cyclic loading can be reduced by selecting materials with enhanced fatigue resistance, optimising the geometry of components to minimise stress concentrators, and incorporating damping elements into the design to partially absorb the energy of cyclic loading. Regular non-destructive testing also enables the timely detection of developing cracks before a critical condition is reached.
Taking account of cyclic loads in a closed-loop system is an essential stage in the design of any machinery and mechanisms, ranging from car engines and aircraft to industrial conveyors and power plants. Failure to take this factor into account leads to a sharp reduction in the service life of equipment, an increased risk of accidents and unforeseen downtime in production processes.
