Load (physics)
All external force values ( forces and moments ) and applied deformations (displacements, temperature- related changes in length caused by constraints , etc.) that act on a component are referred to as load - in short: load .
The effect of a load on the component is its stress in the form of internal stresses .
Basics
According to the Newtonian reaction principle , if the loads do not cancel each other out, this leads to stress in the component, which is expressed as stress and, depending on the rigidity , triggers corresponding changes in shape ( deformations ).
A distinction is made according to the load distribution:
- Point load - is a point load
- Line load - it is shown as a function of the length of action:
- Area load - it is shown as a function of a point on the loaded area:
- A uniformly distributed load is called
- static load and dynamic load - Zother changes with time and is as shown
- Permanent load and moving load - both are constant over time, the former always attacks the same point, but the latter changes the location over time
The load calculation is fundamental in the entire technology for the determination of limit loads, at which the cross-sectional stresses lead to breakage or other failure, and thus for the determination of the necessary load capacity and permissible payload .
Changes over time (dynamic load)
Loads can change over time. A distinction is therefore made between the following cases:
- Load case I : Static or static load - load only increases up to a certain point and remains constant from there. (Example: load is hanging on the rope .)
- Load case II : Swelling load - the force fluctuates (but is always not equal to 0). → Undervoltage is always zero when the load increases, because the workpiece always moves back to its starting position. The only case in which the load cannot be equal to zero is the oscillating load (example: connecting rod screw).
- Load case III : Oscillating or alternating load - The force oscillates from minus to plus and from plus to minus, etc. (example: connecting rod ).
The load cases II and III can be further described by assuming a practically frequent periodic (mostly sinusoidal ) load curve over time. The decisive factor is then the upper or lower maximum of the load curve. Their ratio, also called the load ratio, is the R value
- .
If, in accordance with the sign convention, compressive stresses are provided with a negative and tensile stresses with a positive sign , the following special cases can be distinguished for R , each with its own designation:
R value | designation | ||
---|---|---|---|
Tensile load (case I) | |||
Pressure surge load (case II) | |||
Fluctuating load (case III) |