Failure of a Throttle-Arm Assembly Because of Thread-Root Cracks in the HAZ

2019 ◽  
Keyword(s):  
Thread Root

Stress Concentration at the Root of Bolt Thread

2010 ◽  
Author(s):  
Yasumasa Shoji ◽  
Toshiyuki Sawa
Keyword(s):  
Finite Element Analysis ◽  
Stress Concentration ◽  
Concentration Factor ◽  
The Other ◽  
Special Technique ◽  
Allowable Stress ◽  
Element Analysis ◽  
Bolt Stress ◽  
Thread Root ◽  
External Loads

The bolt strength is determined based on the concentrated bolt stress at the thread roots. The allowable stress is determined so that the thread root will not yield by the pretension and the external loads, using the stress concentration factor obtained as 3 to 5 from experiments. However, the concentration factor is not clear so far, as it is quite difficult to measure the stress at such a localized region. On the other hand, structural analysis, namely finite element analysis, has the possibility to provide the most-likely stress at the thread root. In this paper, a special technique, a.k.a. submodelling, is used to calculate the stress distribution at thread surfaces very precisely. The result will be useful to solve any stress related problems.

scholarly journals Self-loosening behavior of bolt in curvic coupling due to materials ratcheting at thread root

2019 ◽  
Vol 11 (5) ◽  
pp. 168781401984113 ◽  
Author(s):  
Xiangjun Jiang ◽  
Zhi Li ◽  
Yanping Wang ◽  
Fengqun Pan
Keyword(s):  
Thread Root

Fracture Mechanics Integrity Assessment of Stud Bolts Subjected to Cathodic Protection

2020 ◽  
Author(s):  
Mario A. L. de Castro ◽  
Fabio Alves ◽  
Kumarswamy Karpanan ◽  
Anand Venkatesh
Keyword(s):  
Fracture Mechanics ◽  
Cathodic Protection ◽  
Atomic Hydrogen ◽  
Sea Water ◽  
Circular Crack ◽  
Relative Increase ◽  
Maximum Increase ◽  
Integrity Assessment ◽  
Thread Root ◽  
Metallic Parts

Abstract Exposure of metallic parts to cathodic protection (CP) in sea water leads to production and diffusion of atomic Hydrogen into the metal matrix. Absorption of atomic Hydrogen into the metal could lead to hydrogen embrittlement (HE). In order to study the influence of stresses related to HE, FEA and Fracture Mechanics (FM) assessments were performed on a stud bolt threaded geometry. Effects of manufacturing tolerances, interface between nut and stud bolt and a defect in the form of a semi-circular crack placed in highest stress location of a thread root were also considered. Investigations of stress profiles when tension or bending are applied in test samples for measurement of HE threshold were also done, aiming at showing gaps on ASTM F1624-12 [1]. Tolerance assessment shows a relative maximum increase of 260% of nominal linearized membrane plus bending (NLMB) stresses regarding the nut runout [2] and for the proprietary nut geometry, such relative increase drops to 126% of NLMB stresses. Highest Hydrogen concentrations could be observed in the neighborhood of the first loaded thread root. FEA of cracked geometry shows that Hydrogen concentration could increase by around 283% around the crack tip, when compared to stud bolt in unloaded condition. Integrity assessment according to API 579-1 [3] or BS 7910 [4] and tests conducted according to ASTM F1624-12 [1] show less conservative results.

Fatigue and Corrosion Fatigue Failures

2005 ◽  
Author(s):  
Fred V. Ellis
Keyword(s):  
Fracture Surface ◽  
Corrosion Fatigue ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Applied Loading ◽  
Root Area ◽  
Waterwall Tube ◽  
Two Factors ◽  
Fracture Appearance ◽  
Thread Root

A metallurgical failure analysis was performed for a hanger rod and a waterwall tube sample. The hanger is a rigid type and supports a long vertical run of piping. The fracture is in one of the threaded ends and the fracture surface consists of three regions. The outermost portion adjacent to the thread root has ratchet marks that are an indication of fatigue crack initiation. The center portion has concentric, oval shaped beachmarks. The oval shape is consistent with an applied loading due to two bending moments. The inner portion is the final fracture and is approximately 1/4 of the thread root area indicating relatively low remote stresses. The failure mechanism is fatigue based on the beachmarks on the fracture surface and the transgranular cracking. The lower slope waterwall tube failure had a window opening fracture appearance. The axial fractures forming the window are located at the edge of the membrane welds on the cold or backside. There are shallow toe cracks at the membrane weld on the tube outside surface. The fracture surface had multiple, thumbnail-shaped fatigue cracks connected to the inside surface. These fatigue cracks are due to the corrosion fatigue mechanism based on two factors: (1) the stress responsible for their growth is related to the unit thermal cycling and the welded panel geometry near the corner of the boiler, and (2) they are oxidized indicating a corrosion contribution.

scholarly journals Thread Couplings Stress Analysis by Radial Basis Functions Mesh Morphing

2021 ◽  
pp. 114-120
Author(s):  
Michele Calì ◽  
Salvatore Massimo Oliveri ◽  
Marco Evangelos Biancolini
Keyword(s):  
Stress Concentration ◽  
Radial Basis Functions ◽  
Basis Functions ◽  
Mesh Morphing ◽  
Threaded Connection ◽  
Design Variables ◽  
Radial Basis ◽  
Minimum Stress ◽  
Numerical Finite Element ◽  
Thread Root

AbstractTraditional analytical methods are approximate and need to be validated when it comes to predict the tensional behavior of thread coupling. Numerical finite element simulations help engineers come up with the optimum design, although the latter depends on the constraints and load conditions of the thread couplings which are often variable during the system functioning. The present work illustrates a new method based on Radial Basis Functions Mesh Morphing formulation to optimize the stress concentration in thread couplings which is subject to variable loads and constraints. In particular, thread root and fillet under-head drawings for metric ISO thread, which are the most commonly used thread connection, are optimized with Radial Basis Functions Mesh Morphing. In metric ISO threaded connection, the root shape and the fillet under the head are circular, and from shape optimization for minimum stress concentration it is well known that the circular shape becomes seldom optimal. The study is carried out to enhance the stress concentration factor with a simple geometric parameterization using two design variables. Radial Basis Functions Mesh Morphing formulation, performed with a simple geometric parameterization, has allowed to obtain a stress reduction of up to 12%; some similarities are found in the optimized designs leading to the proposal of a new standard. The reductions in the stress are achieved by rather simple changes made to the cutting tool.

scholarly journals The effect of cortical thickness and thread profile dimensions on stress and strain in bone-anchored implants for amputation prostheses

2021 ◽  
Author(s):  
Alexander Thesleff ◽  
Max Ortiz-Catalan ◽  
Rickard Brånemark
Keyword(s):  
Cortical Thickness ◽  
Load Transfer ◽  
Autologous Transplantation ◽  
Implant Design ◽  
Limb Amputation ◽  
Stress And Strain ◽  
Dimensional Changes ◽  
Structural Design Optimization ◽  
Thread Root ◽  
Implant System

<p>Skeletal attachment of limb prostheses ensures load transfer between the prosthetic leg and the skeleton. For individuals with lower limb amputation, these loads may be of substantial magnitude. To optimize the design of such systems, knowledge about the structural interplay between implant design features, dimensional changes, and material properties of the implant and the surrounding bone is needed. Here, we present the results from a parametric finite element investigation on a generic bone-anchored implant system of screw design, exposed to external loads corresponding to average and high ambulatory loading. Of the investigated parameters, cortical thickness had the largest effect on the stress and strain in the bone-anchored implant and in the cortical bone. 36 % – 44 % reductions in maximum longitudinal stress in the bone-anchored implant was observed as a result of increased cortical thickness from 2 mm to 5 mm. Changes in thread depth had larger effect on the maximum stresses in the fixture and the bone than changes in thread root radius within the evaluated parameter space. Stress reductions in the percutaneous abutment were obtained by autologous transplantation of bone tissue distal to the fixture. Results from this investigation may guide structural design optimization for bone-anchored implant systems for attachment of limb prostheses.</p>

Sign in / Sign up

Export Citation Format

Share Document