Fasteners such as hooks and eyelets made of metal, as well as screws, nuts, bolts and rivets are used to join components and metal sheets and sections that must not separate under load. Fastener technology in general, particularly welding and associated technologies, also belong to this group. Relevant standards are DIN EN ISO 9015-1 and -2, as well as DIN EN ISO 14271 and DIN ISO 22826.
The majority of fasteners fall under the category of nuts and bolts in seemingly endless variations; they are one of the most important fastening elements and can be found essentially everywhere. They are used in the construction of complex machinery and equipment, as well as vehicles and buildings. Since mechanical stress is concentrated on these types of connection points, the integrity of fasteners is extremely important.
A wide variety of tests apply to screws/bolts and nuts. This includes tensile tests and hardness tests as well as fatigue tests, torsion tests or Charpy impact tests.
In addition to single-axis tensile loading, shear loads also occur in fasteners in service and can quickly cause a joint to part. Shear tests on joined parts or specimens are therefore essential, particularly where riveted joints are involved. Accurate load application is essential to prevent other forces arising in addition to the shear force and distorting results. ZwickRoell works with you to develop a specification for the correct gripping of the specimen or component and then produces the required arrangement. These test devices can be simple or very complex, but always do exactly what is required of them.
In addition to static loads, fasteners in general are subjected to frequent cyclic loading, including vibrations. Fatigue tests are most quickly and efficiently performed in a vibrophore, which, when using special grips can apply cyclic loads with a maximum force of up to 1000 kN in a frequency range up to approx. 285 Hz. The magnetic drive, which generates controlled resonance in the system, including the specimen, requires minimal power during this test, resulting in highly cost-effective testing.
In what are referred to as H specimens, the individual joints are subjected to common cyclic loading in tension and compression direction, and the fasteners to a shear effect. H specimen holders designed for this test initially distribute the forces over the entire structure. The bending and resultant loosening of the structure can be measured with an extensometer. With the strain values, the testing machine—in this case again a vibrophore—can also control the forces or strain, depending on the test procedure.