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.

Tensile and fatigue strength of ultrathin copper films

Abstract: Tensile and fatigue tests of ultrathin Cu films were conducted using a micro-force testing system. Fatigue strength as a function of film thickness was measured under the constant total strain range control at a frequency of 10 Hz. The experimental results exhibit that both yield strength and fatigue lifetime are dependent on film thickness. Fatigue damage behavior in the 100 nm thick Cu films with nanometer-sized grains is different from that in the micrometer-thick Cu films with large grains observed before. A comparison of the present results with those reported in literatures is conducted. Possible fatigue strengthening mechanism in the ultrathin Cu films is discussed.

An Investigation of the Microstructure and Fatigue Behavior of Additively Manufactured AISI 316L Stainless Steel with Regard to the Influence of Heat Treatment

Abstract: To exploit the whole potential of Additive Manufacturing, it is essential to investigate the complex relationships between Additive Manufacturing processes, the resulting microstructure, and mechanical properties of the materials and components. In the present work, Selective Laser Melted (SLM) (process category: powder bed fusion), Laser Deposition Welded (LDW) (process category: direct energy deposition) and, for comparison, Continuous Casted and then hot and cold drawn (CC) austenitic stainless steel AISI 316L blanks were investigated with regard to their microstructure and mechanical properties. To exclude the influence of surface topography and focus the investigation on the volume microstructure, the blanks were turned into final geometry of specimens. The additively manufactured (AM-) blanks were manufactured in both the horizontal and vertical building directions. In the horizontally built specimens, the layer planes are perpendicular and in vertical building direction, they are parallel to the load axis of the specimens. The materials from different manufacturing processes exhibit different chemical composition and hence, austenite stability. Additionally, all types of blanks were heat treated (2 h, 1070 °C, H2O) and the influence of the heat treatment on the properties of differently manufactured materials were investigated. From the cyclic deformation curves obtained in the load increase tests, the anisotropic fatigue behavior of the AM-specimens could be detected with only one specimen in each building direction for the different Additive Manufacturing processes, which could be confirmed by constant amplitude tests. The results showed higher fatigue strength for horizontally built specimens compared to the vertical building direction. Furthermore, the constant amplitude tests show that the austenite stability influences the fatigue behavior of differently manufactured 316L. Using load increase tests as an efficient rating method of the anisotropic fatigue behavior, the influence of the heat treatment on anisotropy could be determined with a small number of specimens. These investigations showed no significant influence of the heat treatment on the anisotropic behavior of the AM-specimens.

A study of the effect of nanostructured surface layers on the fatigue behaviors of a C-2000 superalloy

Abstract: Fatigue behaviors of a Ni-based C-2000 superalloy subjected to the surface nanocrystallization and hardening (SNH) process were investigated. The influence of the SNH processing condition on the fatigue properties of the material was analyzed. The near-surface structures of the SNH-treated specimens were characterized by means of the scanning-electron microscopy, X-ray diffraction, and transmission-electron microscopy. It is shown that the SNH is an effective method to render the material with the features, such as a nanostructured and work-hardened surface layer as well as compressive residual stresses, which can pronouncedly improve the fatigue strength of the material. However, excessive treatments deteriorate the fatigue properties, and the surface contaminations are considered to be the main reason.

An engineering method for estimating notch-size effect in fatigue tests on steel

Abstract: Neuber's proposed method of calculating a practical factor of stress concentration for parts containing notches of arbitrary size depends on the knowledge of a "new material constant" which can be established only indirectly. In this paper, the new constant has been evaluated for a large variety of steels from fatigue tests reported in the literature, attention being confined to stresses near the endurance limit. Reasonably satisfactory results were obtained with the assumption that the constant depends only on the tensile strength of the steel. Even in cases where the notches were cracks of which only the depth was known, reasonably satisfactory agreement was found between calculated and experimental factors. It is also shown that the material constant can be used in an empirical formula to estimate the size effect on unnotched specimens tested in bending fatigue.

Fatigue failure in denture base polymers

Abstract: Although well-fitting dentures of adequate thickness seldom exhibit fatigue failure in service, a very small percentage of the millions of denture wearers have well-fiting dentures. Fatigue failure is a very real problem in these dentures, in the well-fitting single upper denture occluding against natural lower teeth, and in all dentures with soft liners. We can make dentures more resistant to fatigue failure by using a few precautions. First, the heat-curing resins are much more resistant to this failure; therefore, use of a heat-curing acrylic resin is indicated. Second, fine-polymer beads increase fatigue strength many times, so a fine-grained polymer should be used. Finally, stress concentrators should be avoided. Most important would be the elimination of sharp surface contours, such as deep notches for low frenum attachments, and prominent rugae patterns. A prominent frenum attachment has little function and is not beneficial to the completely edentulous individual. It is a simple procedure to eliminate the frenum at the time of extraction of the anterior teeth. Any particle acts as a stress concentrator; therefore, acrylic dentures should be fabricated in a relatively dust-free atmosphere such as that used for porcelain work. Fibers and the surface defects that they produce act as stress concentrators, and this should be recognized if a material with fibers is used. Rayon or nylon fibers are used commercially. 20 The use of acrylic fibers should correct this weakness.