Effect of Helix Angle on the Stress Intensity Factor of a Cracked Threaded Bolt
01 Apr 2013-Journal of Pressure Vessel Technology-transactions of The Asme (American Society of Mechanical Engineers)-Vol. 135, Iss: 2, pp 021202
About: This article is published in Journal of Pressure Vessel Technology-transactions of The Asme.The article was published on 2013-04-01. It has received 6 citations till now. The article focuses on the topics: Stress intensity factor & Helix angle.
TL;DR: In this article, a parametric analysis was carried out for asymmetric spur gears to examine the fracture behavior under mixed-mode fracture condition and explore the significance of each gear parameters.
Abstract: As a high power transmission capacity and long durability constitute an essential requirement for mechanical machinery, the mechanical transmission gears need to be modified to improve the performance. The increasing drive side pressure angle is one of the methods for enhancing load-carrying capacity of the spur gear. The fracture characteristics of asymmetric gears need to be investigated to estimate the fatigue life. The location and magnitude of stress intensity factors mainly depend on gear tooth geometry, gear parameters, crack tip location, and applied force. Most of the literature study of fracture analysis carried out for the symmetric gears and the majority of them are two-dimensional analysis. In this study, a parametric analysis carried out for asymmetric spur gears to examine the fracture behaviour under mixed-mode fracture condition and explore the significance of each gear parameters. The maximum bending stress location for each gear pair is determined and the crack is introduced at that region. The stress intensity factor (SIF) for each mode is estimated and the effective stress intensity factor at each node along the face width is determined. In addition, the effect of opening mode, sliding mode and tearing mode on effective stress intensity factor for fillet crack is examined. This analysis inferred that the effect of opening mode fracture is predominant in the effective stress intensity factor irrespective of gear parameters.
TL;DR: In this article, an axial-tensile fatigue test under a stress ratio of 0.5 was performed on 21 specimens of high-strength bolts to investigate the constant-amplitude fatigue performance of grade 8.8 M24 high strength bolts.
Abstract: Investigating the fatigue performance of high-strength bolt is essential to prevent related accidents. An axial-tensile fatigue test under a stress ratio of 0.5 was performed on 21 specimens of high-strength bolts to investigate the constant-amplitude fatigue performance of grade 8.8 M24 high-strength bolts. Based on experimental results, S–N curves were obtained through regression analysis, and fractographic analysis was conducted on typical specimens. Moreover, the results were compared with the existing fatigue experimental results and standards. Further, a finite element model was established to analyze the stress distribution of the bolts. It was found that the fatigue strength of the high-strength bolt at 2 × 106 cycles under a stress ratio of 0.5 was 89.76 MPa, which is 1.60 to 1.87 times greater than the values specified in the current standards. Through the comparison of the fatigue tests under stress ratios of 0.3, 0.5, and 0.8, the fatigue strength decreased as the stress ratio increased. Additionally, two main fatigue failure modes were found, with most bolts fracturing at the root of the first loaded thread; this is confirmed by the stress concentration location obtained from finite element analysis. The fracture morphology of the bolts exhibited a single-point fatigue source and possessed obvious fatigue fracture characteristics. It was concluded that the area of the fatigue propagation region was basically inversely proportional to stress ratio.
10 Jun 2016
TL;DR: In this article, a methodologie d'analyse tribologique is proposed for demontering an assemblage boulonnes without modifying the conditions of contact lors du desserrage, le devissage, la perte d'etancheite, l'initialisation de fissures, etc.
Abstract: Depuis l'utilisation des boulons au XVeme siecle pour assembler deux pieces, les assemblages boulonnes posent des questions quant a la comprehension de leur fonctionnement et de leurs defaillances, telles que la variation de la tension de serrage entrainant, le desserrage, le devissage, la perte d'etancheite, l'initialisation de fissures, ... Pour comprendre leur fonctionnement, une methodologie d'analyse tribologique a ete mise en place, permettant de demonter un assemblage boulonne sans le desserrer, afin de ne pas modifier les conditions de contact lors du desserrage. Ainsi, toutes les interfaces d'assemblages (‘‘filets’’ ecrou/vis et ‘‘autres que filets’’) formant des triplets tribologiques, ont ete etudiees durant les trois phases de leur cycle de vie (fabrication, serrage, service) par le biais de cas-tests de materiaux differents. Un dialogue interactif entre les experimentations (correlations d'images, expertises) et la simulation numerique (Elements Finis, Elements Discrets) a permis de degager des interpretations, notamment concernant les trois phases. Lors de la fabrication, le roulage des vis engendre des transformations tribologiques superficielles au niveau des sous-surfaces des filets formes. Le cœur des vis (noyau) restant non-deforme, ce procede cree ainsi une difference de microstructure au sein de ces vis, ce qui est une source d'alteration de leurs proprietes en fatigue. Lors du serrage, il se forme a l'interface ‘‘filets’’ une mixture de troisiemes corps ‘‘sec-solide’’, accommodant la vitesse entre la vis et l'ecrou. Cette mixture resulte d'une reactivite entre une graisse utilisee pour le serrage et des particules, detachees d'un revetement applique sur les filets d'ecrous et/ou de vis. En fin de serrage, une partie de la mixture reste piegee entre les filets, jouant le role de maintien de la tension de serrage. Dans ces conditions, il apparait que le frottement varie en fonction de la rheologie de la mixture, conditionnant la variation de la tension de serrage. En service, des instabilites de contact (glissement, decollement, ...) ont ete identifiees au niveau des interfaces. Ces instabilites engendrent dans les interfaces ‘‘autres que filets’’ la formation d'un troisieme corps oxyde. Ce dernier constitue un surplus de matiere qui peut entrainer l'augmentation des contraintes mecaniques dans les assemblages. A l'interface ‘‘filets’’ ecrou/vis, il a ete constate que si la mixture de troisiemes corps piegee en serrage n'est pas cohesive, elle est extrudee des contacts, initialisant la perte de la tension de serrage. A partir de ces interpretations, des interactions entre plusieurs circuits tribologiques conduisent a converger vers un scenario de fonctionnement des assemblages boulonnes, permettant de solutionner leurs defaillances par la re-conception (mise en place de gorge de decharge, ...).
TL;DR: In this article , the effect of backup ratio on the fatigue crack behavior of asymmetric and asymmetric spur gear under mix mode fracture is investigated, and the authors give valuable guidelines for designing asymmetric spars gears to reduce the weight without compromising the service life.
Abstract: Gears are one of the most important components in most mechanical machines, automobiles, and other wind mills. The gears are subjected to repeated fillet stress, which causes them to develop root fracture leading to the failure of the power transmission system. Hence, the gear should be resistant to fracture. Furthermore, reduced weight and size of the gear is necessary to reduce the overall weight of the transmission system. The effect of backup ratio on the fatigue crack behaviour of symmetric and asymmetric spur gear under mix mode fracture is investigated in this study. The strain energy release rate (SERR), T-stress, and stress intensity factors (SIFs) of thick and thin rim asymmetric spur gear under mixed-mode condition are determined. Additionally, the effective SIF and the shape factor are evaluated for all spur gears. It is noticed that the fracture resistance of asymmetric spur gear (ANCR) increases with an increase in rim thickness. Further, an increase in backup ratio increases the stability of the crack and hence retards the crack growth. In addition, the influence of backup ratio on fracture resistance decreases with an increase in drive side pressure angle. Hence, an increase in pressure angle at drive side increases the crack stability, and the resistance towards fracture. The inference of this study gives valuable guidelines for designing asymmetric spur gears to reduce the weight without compromising the service life.
20 Oct 2020
TL;DR: In this paper, the elastic-plastic fracture performance of the threaded connection is simulated under both make-up torque and bending moment, and explicit relationships between characteristic J-integrals and the crack depth are obtained for the DSS.
Abstract: For a positive displacement motor (PDM), the threaded joint connecting drive shaft shell (DSS) and universal shaft shell that is close to the bit is inclined to fracture. In this paper, elastic-plastic fracture performance of the threaded connection is simulated under both make-up torque and bending moment. Firstly, an FE model, which includes a cracked external thread of the DSS and an engaging internal thread of the universal shaft shell, is established and validated. Secondly, influences of both plastic deformation and the helix angle on fracture properties of the cracked thread are evaluated quantitatively. Meanwhile interactions between two cracks are also discussed. Finally, under the two kinds of loading conditions, i.e. loaded by pre-load only and loaded by both pre-load and bending moment, explicit relationships between characteristic J-integrals and the crack depth are obtained for the DSS.
TL;DR: In this article, the authors presented the stress-intensity factors for shallow and deep semi-elliptical surface cracks in plates subjected to tension and verified the accuracy of the three-dimensional finite-element models employed.
Abstract: Surface cracks are among the more common flaws in aircraft and pressure vessel components. Several calculations of stress-intensity factors for semi-elliptical surface cracks subjected to tension have appeared in the literature. However, some of these solutions are in disagreement by 50-100%. In this paper, stress-intensity factors for shallow and deep semi-elliptical surface cracks in plates subjected to tension are presented. To verify the accuracy of the three-dimensional finite-element models employed, convergence was studied by varying the number of degrees of freedom in the models from 1500 to 6900. The 6900 degrees of freedom used here were more than twice the number used in previously reported solutions. Also, the stress-intensity variations in the boundary-layer region at the intersection of the crack with the free surface were investigated.
TL;DR: In this paper, an elliptical-arc surface crack in a round bar under cyclic axial loading with constant amplitude is considered, and the stress-intensity factor along the crack front is calculated through a finite-element analysis by employing isoparametric solid elements.
Abstract: An elliptical-arc surface crack in a round bar under cyclic axial loading with constant amplitude is considered. The stress-intensity factor along the crack front is calculated through a finite-element analysis by employing isoparametric solid elements. Then the fatigue crack propagation is examined by means of the Paris-Erdogan law. The aspect ratio a/b of the initial flaw is made to vary from 0.0 (straight crack front) to 1.0 (circular-arc crack front). Moreover, different material properties and loading parameters are considered. For each case being analysed, it is shown that the surface cracks tend to follow preferred propagation paths, with the flaw aspect ratio converging to a value in the range 0.6–0.7.
••01 Jun 1948
TL;DR: In this paper, it was shown that the load distribution along the length of a nut is not uniform owing to the strains set up in the bolt and nut under load, and that the maximum intensity of loading occurs at the bearing face of the nut, and may be from two to four or more times the mean, depending on the thread form, the proportions of the members, and the degree of lubrication.
Abstract: The distribution of load along the length of a nut is not uniform owing to the strains set up in the bolt and nut under load. These strains are analysed and the load distribution along the thread helix deduced. It is shown that the load may be taken as concentrated at mid-depth of the threads. In the normal bolt and nut case the maximum intensity of loading occurs at the bearing face of the nut, and may be from two to four or more times the mean, depending on the thread form, the proportions of the members, and the degree of lubrication; the maximum intensity is almost independent of the length of nut (unless yielding occurs). Possible methods of improving the load distribution are discussed—differential pitch, tapered threads, and the use of a softer material for the nut. The load distribution in the turnbuckle case is more favourable than in the bolt and nut case, and can theoretically be made uniform by suitably boring out the inner and shaping the outer member; this condition can be approached in prac...
TL;DR: In this paper, the fatigue growth of an edge flaw in a round bar under cyclic tension or bending loading is examined, using a two-parameter numerical model, and it is shown that the crack front evolution is defined by a very small number of parameters, which varies during crack growth.
Abstract: The fatigue growth of an edge flaw in a round bar under cyclic tension or bending loading is examined, using a two-parameter numerical model. First, it is shown that the crack front evolution is defined by a very small number of parameters, which varies during crack growth. Approximated solutions for both the crack propagation path and the stress intensity factor are derived, and the fatigue predictions using this simple analytical method are finally compared with the numerical results.
TL;DR: In this article, generalized stress intensity factors for a V-shaped notched round bar under tension, bending, and torsion were calculated using the singular integral equation of the body force method.
Abstract: In this study, generalized stress intensity factors KI,λ1, KII,λ2, and KIII,λ4 are calculated for a V-shaped notched round bar under tension, bending, and torsion using the singular integral equation of the body force method. The body force method is used to formulate the problem as a system of singular integral equations, where the unknown functions are the densities of body forces distributed in an infinite body. In order to analyze the problem accurately, the unknown functions are expressed as piecewise smooth functions using three types of fundamental densities and power series, where the fundamental densities are chosen to represent the symmetric stress singularity and the skew-symmetric stress singularity. Generalized stress intensity factors at the notch tip are systematically calculated for various shapes of V-shaped notches. Normalized stress intensity factors are given by using limiting solutions; they are almost determined by notch depth alone, and almost independent of other geometrical parameters. The accuracy of Benthem–Koiter’s formula proposed for a circumferential crack is also examined through the comparison with the present analysis.