Safety factor, in the strength of materials, defines the relation between the design load that ensures safe operation of a structure and the maximum load that is theoretically permissible. Depending on the purpose of the object and the conditions in which it works, various definitions and values of the safety factor are used
1) The safety factor in terms of stress is the ratio of the permissible stress (the ultimate strength, the yield strength, or the fatigue limit under alternating loads) to the greatest stress for a given type of loading.
2) The safety factor in terms of limit loads is the ratio of the load at which the structure loses its load-bearing capacity to the design load.
3) The safety factor in terms of limit deformation is the ratio of the load that produces the maximum permissible characteristic deformation in the structure as a whole or in any of its elements (a deflection, a change in the distance between nodes and the like) to the design load.
The purpose of the safety factor is to take account of the mechanical properties of the material, the probability of accidental overloads, the degree of reliability of the calculation and of the input data, and the possibility of unforeseen defects (shrinkage cavities, pits and others). The choice of a value for the safety factor takes account of the need to economise on material, and in a number of cases it is bound up with the problem of designing a structure of minimum weight (spacecraft and aircraft, for example). The smallest values of the safety factor are used in objects intended for a single short-term use; the largest, in structures for long-term use, especially under dynamic loads.
1) The safety factor in terms of stress is the ratio of the permissible stress (the ultimate strength, the yield strength, or the fatigue limit under alternating loads) to the greatest stress for a given type of loading.
2) The safety factor in terms of limit loads is the ratio of the load at which the structure loses its load-bearing capacity to the design load.
3) The safety factor in terms of limit deformation is the ratio of the load that produces the maximum permissible characteristic deformation in the structure as a whole or in any of its elements (a deflection, a change in the distance between nodes and the like) to the design load.
The purpose of the safety factor is to take account of the mechanical properties of the material, the probability of accidental overloads, the degree of reliability of the calculation and of the input data, and the possibility of unforeseen defects (shrinkage cavities, pits and others). The choice of a value for the safety factor takes account of the need to economise on material, and in a number of cases it is bound up with the problem of designing a structure of minimum weight (spacecraft and aircraft, for example). The smallest values of the safety factor are used in objects intended for a single short-term use; the largest, in structures for long-term use, especially under dynamic loads.