The load-carrying capacity test program contains the first criterion condition for the force structure – confirmation of the design and determination of the actual load-carrying capacity of the assembly under static application of design loads, which is the main purpose of the test.
As a rule, the program provides a stepwise application of loads for several design cases. The combination of loads, their magnitudes, the order of application by design cases, ultimate and subcritical strength conditions or the achievement of ultimate deformations (displacements) are set in a table, ribbon or three-dimensional graph.
Each design loading case is divided into two levels: operational and design. The operational level of loading is divided into 6 – 10 stages to perform preliminary measurements of displacements and VAT in the elastic region and simultaneous development and control of reproducibility of linear loading. At this level, the zones and cross-sections of possible failure or plastic hinge occurrence are determined on the basis of the VAT study.
Observation areas are marked during testing before fracture, remote instrumentation for measuring parameters at fracture is installed and graded. Depending on the task, optical, polarization-optical, moiré (raster) means of VAT registration are installed, high-speed photo and movie registration, videorecording of fracture dynamics or loss of stability by stages are used. Special safety measures are taken into account, especially when testing high-strength brittle materials and for objects accumulating significant elastic energy before fracture, for example, when testing shells of large volumes by compressible gas (air) supercharging.
Loading to design loads is carried out once, continuously increasing the load level from operational to design, and, without stopping the loading, bring the test to the maximum loads, noting a sharp (or smooth) decrease in load at failure of elements, loss of bearing capacity (stability). The rate of loading is stipulated in the program and in the specifications for the energy requirements of the stand. For static loading of metal structures, the critical speed is when the error of load reproduction due to the attached masses of the loading system becomes greater than 1% of the given current force value, and all transients from the beginning to the end of the deformation diagram depend only on the stiffness of the system, not on its mass.
In the case of carrying capacity tests with simultaneous thermal effect on the object, carried out by means of radiant heating or in chambers-thermostats, the modes of mechanical loading and heating (heating) rates are set by special schedules, taking into account the heat capacity of the specimen and the system, inertia of heat transfer regulation, dissipation and power of radiators. The program is implemented by an automatic system of output and maintenance of the temperature regime on the object in time or as a function of mechanical load. The methodology of carrying capacity testing of scale models of large-scale objects requires a rigorous theoretical justification and considerable research.