FE evaluation of 4-point bending test for fatigue cracking assessment

Fatigue lives of asphalt mixtures are, in general, significantly affected by the test method and mode of loading. Previous studies have evaluated the different commonly used test methods on the base of their simplicity, ability to simulate test conditions and applicability of the test results to pavement design against fatigue cracking. From this point of view, the tests based on the principle of simple flexure are commonly preferred. Amongst these, the four-point bending test (also known as third point flexure test) was focused where, unlike other tests, the failure of the specimen occurs in an area of uniform bending moment. Loading conditions, testing set-up and internal stresses or strains imposed by clamps at the load or reaction points are all factors that are found to influence the specimen response to the test. In this study, a detailed FEM analysis of the structure and geometry of a four-point bending frame, designed at the Nottingham Transportation Engineering Centre (NTEC) of the University of Nottingham, was performed, describing how geometric constraints and dynamic actions can affect the estimation of the fatigue life of asphalt prismatic specimens with various stiffnesses. In conclusion, the dominating causes of imprecision in the tests results are outlined and the main issues that should be taken into consideration during the design and optimization of this non-standardized equipment are indicated.