Fastener Testing

Standard material testing of screws is very versatile and places extensive and complex demands on the testing system. On the one hand, there are screws in a variety of sizes and types, which must be guaranteed to be clamped as specified in the ISO 898-1 standard, and on the other hand the standard describes various types of tests. In order to be able to cover all of these different requirements, Hegewald & Peschke offers a clamping device with a modular accessory system. 

Appropriate sample holders are inserted into a clamping device specially developed for screw testing. This enables simple and quick sample clamping and prevents the introduction of transverse forces into the screw. The sample holders are adapted to specific screw sizes as well as to carry out different types of tests, such as diagonal pull tests. This ensures the entire range of screws can be tested with one clamping device, from very short to very long screws with large threads; to include turned screws, finished shoulder head screws, nuts and even complete sets; as well as standard thread and fine thread screws.

Another challenge when testing screws according to DIN EN ISO 898-1 is the determination of special parameters, such as the elongation at break ‘A f’ and the 0.0048 ‘d’ yield strength of entire screws. For this purpose, an attachment strain gauge is used in the testing system, which records the change in length over the total length of the screw. To do this, the tactile strain gauge is placed on the screw from above and below in specially designed openings in the sample holder and in the clamping device. 

All parameters for carrying out the tensile test are set in the LabMaster material testing software, according to ISO 6892-1. During the test, the testing machine control regulates the testing speed in accordance with the specifications of ISO 898-1 – including speed switching when the 0.0048 ‘d’ yield strength ‘F pf’ is reached. The resulting force displacement curves and the characteristic values are then automatically determined and displayed in the testing software.

The clamping devices for screws are optimally tailored for use in the testing machines of the inspekt series from Hegewald & Peschke Meß-und Prüftechnik GmbH. For testing screws with different strength classes and sizes, the tensile testing machines are available in a wide load range with test forces of up to 2,000kN. The clamping devices are characterised by great flexibility and always ensure standard testing according to DIN EN ISO 898-1. In addition, thanks to their modular structure, they can also be expanded later if the customer develops new testing requirements.