Issue 75

M. Nikhamkin et alii, Fracture and Structural Integrity, 75 (2026) 390-398; DOI: 10.3221/IGF-ESIS.75.28

constant cyclic loading parameters: minimum σ min and maximum σ max stresses in the cycle (Fig. 4). In each successive block the maximum stress increases by a step Δσ max . After each block the specimen is allowed to cool to its initial temperature. During loading, the temperature field on the specimen surface is recorded by an infrared camera. In the present work an NEC TH9100 WR ProNew camera operating in the 8–14 µm range with sensitivity 0.02 °C and a 320 × 240 pixel detector was used. To reduce thermography errors, the room temperature is maintained constant during testing, and external infrared sources are screened. The specimen surface is coated with black matte paint before testing.

Figure 3: Experimental set - up. 1 – specimen, 2 – Testronic - 50 testing machine, 3 – infrared camera.

Figure 4: Block cyclic loading of a specimen (top) and typical temperature change on the specimen surface (bottom). Developing a fatigue - limit determination method for a particular material involves, in addition to selecting equipment and specimen type, a justified choice of the number of loading blocks and their parameters—initial and final σ max values and loading step Δσ max . In addition, a region on the specimen surface for temperature recording must be specified, taking into account the non - uniform temperature field, and a heating indicator parameter must be selected in accordance with the IRT procedure. Previous works [24] developed accelerated fatigue - limit assessment procedures for polymer composite materials within the IRT framework. They proposed processing elements to improve data accuracy. Fig. 5 shows the temperature increment on the specimen surface θ =T-T 0 (where T and T 0 are the current and initial temperatures) during cyclic loading with constant stress amplitude above the fatigue limit Errore. L'origine riferimento non è stata trovata. . Three stages of self - heating are distinguished: stage I – temperature increases due to energy dissipation associated with fatigue damage accumulation; stage II – temperature stabilises because all generated heat is dissipated to the

393