Fatigue limit

About: Fatigue limit is a research topic. Over the lifetime, 20489 publications have been published within this topic receiving 305744 citations. The topic is also known as: endurance limit & fatigue strength.

Characterization and High-Temperature Mechanical Behavior of an Oxide/Oxide Composite

Abstract: An oxide/oxide ceramic fiber-matrix composite (CMC) has been extensively characterized for high-temperature aerospace structural applications. This CMC is called GEN-IV™, and it has a porous and cracked aluminosilicate matrix reinforced by 3M Nextel 610™ alumina fibers woven in a balanced eight harness weave (8HSW). This CMC has been specifically designed without an interphase between the fiber and matrix, and it relies on the porous matrix for flaw tolerance. Stress-strain response is nearly linear to failure and without a well-defined proportional limit in tension and compression. In-plane shear and interlaminar strength increases with increasing temperature. The 1000°C fatigue limit in air at 105 cycles is 160 MPa, and the residual tensile strength of run-out specimens is not affected by the fatigue loading. The creep-rupture resistance above 1000°C is relatively poor, but it can be improved with a more-creep-resistant fiber.

Fatigue crack propagation resistance of highly crosslinked polyethylene.

Abstract: A higher degree of cross-linking has been shown to improve wear properties of ultra-high molecular weight polyethylene in laboratory studies. However, cross-linking can also affect the mechanical properties of ultra-high molecular weight polyethylene. Fatigue crack propagation resistance was determined for electron beam cross-linked ultra-high molecular weight polyethylene and compared with gamma irradiation cross-linked and noncross-linked polyethylene fatigue specimens. Crosslinking was done with different dosages of irradiation followed by melting. For one irradiation dose (50 kGy) extrusion and molding processes were compared. A fracture mechanics approach was used to determine how the degree of cross-linking affects resistance to crack propagation in ultra-high molecular weight polyethylene. Fatigue crack propagation resistance was reduced in proportion to the irradiation dose. The type of irradiation (gamma or electron beam) or manufacturing method (extrusion or molding) did not affect fatigue crack propagation resistance. The reduced fatigue strength of highly cross-linked ultra-high molecular weight polyethylene could lead to mechanical failure in conditions that are associated with cyclic local tensile stresses.

S-N Lines for Welded Thin Joints — Suggested Slopes and FAT Values for Applying the Notch Stress Concept with Various Reference Radii

Abstract: An assessment of thin welded structures with actual IIW design lines results in an overestimation of fatigue lives (strengths) at high load levels and a conservative estimation at low load levels, in many cases, independently of the applied fatigue assessment approach (nominal, structural or notch stress). This is mainly due to the slopes of the design S-N line k = 3.0 for normal and k = 5.0 for shear stresses, which are valid for thick and stiff structures. To overcome this inconsistency for welded thin and flexible structures, the slopes k = 5.0 for normal and k = 7.0 for shear stresses are suggested, keeping the already known FAT values derived for the notch stress concept variants with rref = 1.0, 0.3 or 0.05 mm, respectively. However, the slope is not only determined by plate thickness; it is the result of an interaction between thickness, local geometry (stress concentration), structural stiffness, loading mode and last but not least residual stresses. This complexity makes it difficult to identify the driving parameters and to predict the slope of the S-N line in many cases.

Life prediction methodology for GFRP laminates under spectrum loading

Abstract: A complete life prediction methodology for glass fiber reinforced plastic laminates accounting for plane stress states and spectrum loading is presented in this paper. Fatigue strength allowables in the laminate symmetry axes are derived by direct characterization for a number of different constant amplitude loading cases. Experimental results from tests inducing plane stress states, conducted using two different loading spectra of variable amplitude, were used to validate the entire methodology. The first loading spectrum is a modified version of the well known in wind turbine rotor blade research activities, WISPERX, while the second one is derived through aeroelastic simulations of a realistic loading case for a small glass fiber reinforced polyester rotor blade. The effectiveness of the methodology is investigated and correlated to several parameters that affect life prediction, such as, type of loading, baseline data, damage accumulation rule, etc.