Publication

Size effects in the fatigue behavior of welded tubular bridge joints

Abstract

Tubular space trusses for bridge applications use thick-walled tubes. The reduction in fatigue resistance due to geometrical size effects is thus an important issue. In order to carry out a thorough study, both fatigue tests on large-scale specimens and advanced 3D crack propagation modelling were carried out at ICOM/EPFL. The study is limited to circular hollow sections (CHS) K-joints. An alternate current potential drop (ACPD) system is used to measure crack depth on nodes of the tested truss specimens. The results obtained from the tests are given in the paper in terms of S-N data, crack depth versus number of cycles and deduced crack propagation rates. The numerical model was developed using the dual boundary elements method (DBEM), software BEASYTM, and was validated with fatigue tests data. The stress intensity factors (SIF) along the doubly curved crack front at different crack depths were obtained.With this model, a parametric study investigates the influence of geometry, size and load case on fatigue life. The results of both proportional and non-proportional sizing effects on fatigue strength are presented. The paper shows that size effects (proportional and non-proportional) can be expressed as a function of the non-dimensional parameters and chord thickness. Keywords: Structural steel, fatigue, size effects, large-scale tests, boundary element method.

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Related concepts (33)
Fatigue (material)
In materials science, fatigue is the initiation and propagation of cracks in a material due to cyclic loading. Once a fatigue crack has initiated, it grows a small amount with each loading cycle, typically producing striations on some parts of the fracture surface. The crack will continue to grow until it reaches a critical size, which occurs when the stress intensity factor of the crack exceeds the fracture toughness of the material, producing rapid propagation and typically complete fracture of the structure.
Fatigue
Fatigue describes a state of tiredness (which is not sleepiness) or exhaustion. In general usage, fatigue often follows prolonged physical or mental activity. When fatigue occurs independently of physical or mental exertion, or does not resolve after rest or sleep, it may have other causes, such as a medical condition. Fatigue (in a medical context) is complex and its cause is often unknown. Fatigue is associated with a wide variety of conditions including autoimmune disease, organ failure, chronic pain conditions, mood disorders, heart disease, infectious diseases and post-infectious disease states.
Proportional representation
Proportional representation (PR) refers to a type of electoral system under which subgroups of an electorate are reflected proportionately in the elected body. The concept applies mainly to political divisions (political parties) among voters. The essence of such systems is that all votes cast - or almost all votes cast - contribute to the result and are effectively used to help elect someone - not just a bare plurality or (exclusively) the majority - and that the system produces mixed, balanced representation reflecting how votes are cast.
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