scholarly journals The Effects of Laser Marking and Symbol Etching on the Fatigue Life of Medical Devices

2013 ◽  
Vol 2013 ◽  
pp. 1-6 ◽  
Author(s):  
P. J. Ogrodnik ◽  
C. I. Moorcroft ◽  
P. Wardle
Keyword(s):  
Fatigue Life ◽  
Mechanical Performance ◽  
Stress Amplitude ◽  
Worst Case ◽  
Laser Marking ◽  
Life Issues ◽  
Stress Environment ◽  
Medical Component ◽  
Surprising Fact ◽  
Fast Fracture

This paper examines the question;“ does permanent laser marking affect the mechanical performance of a metallic medical component?” The literature review revealed the surprising fact that very little has been presented or studied even though intuition suggests that its effect could be detrimental to a component's fatigue life. A brief investigation of laser marking suggests that defects greater than 25 μm are possible. A theoretical investigation further suggests that this is unlikely to cause issues with relation to fast fracture but is highly likely to cause fatigue life issues. An experimental investigation confirmed that laser marking reduced the fatigue life of a component. This combination of lines of evidence suggests, strongly, that positioning of laser marking is highly critical and should not be left to chance. It is further suggested that medical device designers, especially those related to orthopaedic implants, should consider the position of laser marking in the design process. They should ensure that it is in an area of low stress amplitude. They should also ensure that they investigate worst-case scenarios when considering the stress environment; this, however, may not be straightforward.

Fatigue Life of the Human Teeth: A Continuum Damage Approach

2019 ◽  
Vol 43 ◽  
pp. 1-19
Author(s):  
Theddeus Tochukwu Akano
Keyword(s):  
Fatigue Life ◽  
Damage Mechanics ◽  
Stress Amplitude ◽  
Continuum Damage Mechanics ◽  
Continuum Damage ◽  
Elastoplastic Model ◽  
Human Teeth ◽  
Proposed Model ◽  
Number Of Cycles ◽  
Cycles To Failure

Normal oral food ingestion processes such as mastication would not have been possible without the teeth. The human teeth are subjected to many cyclic loadings per day. This, in turn, exerts forces on the teeth just like an engineering material undergoing the same cyclic loading. Over a period, there will be the creation of microcracks on the teeth that might not be visible ab initio. The constant formation of these microcracks weakens the teeth structure and foundation that result in its fracture. Therefore, the need to predict the fatigue life for human teeth is essential. In this paper, a continuum damage mechanics (CDM) based model is employed to evaluate the fatigue life of the human teeth. The material characteristic of the teeth is captured within the framework of the elastoplastic model. By applying the damage evolution equivalence, a mathematical formula is developed that describes the fatigue life in terms of the stress amplitude. Existing experimental data served as a guide as to the completeness of the proposed model. Results as a function of age and tubule orientation are presented. The outcomes produced by the current study have substantial agreement with the experimental results when plotted on the same axes. There is a notable difference in the number of cycles to failure as the tubule orientation increases. It is also revealed that the developed model could forecast for any tubule orientation and be adopted for both young and old teeth.

Uniaxial Ratcheting and Low-Cycle Fatigue Failure of U75V Rail Steel

2016 ◽  
Vol 853 ◽  
pp. 246-250 ◽  
Author(s):  
Tao Fang ◽  
Qian Hua Kan ◽  
Guo Zheng Kang ◽  
Wen Yi Yan
Keyword(s):  
Fatigue Life ◽  
Strain Amplitude ◽  
Stress Ratio ◽  
Stress Amplitude ◽  
Rail Steel ◽  
Low Cycle Fatigue ◽  
Mean Stress ◽  
Cycle Fatigue ◽  
Ratcheting Strain ◽  
Cyclic Straining

Experiments on U75V rail steel were carried out to investigate the cyclic feature, ratcheting behavior and low-cycle fatigue under both strain- and stress-controlled loadings at room temperature. It was found that U75V rail steel shows strain amplitude dependent cyclic softening feature, i.e., the responded stress amplitude under strain-controlled decreases with the increasing number of cycles and reaches a stable value after about 20th cycle. Ratcheting strain increases with an increasing stress amplitude and mean stress, except for stress ratio, and the ratcheting strain in failure also increases with an increasing stress amplitude, mean stress and stress ratio. The low-cycle fatigue lives under cyclic straining decrease linearly with an increasing strain amplitude, the fatigue lives under cyclic stressing decrease with an increasing mean stress except for zero mean stress, and decrease with an increasing stress amplitude. Ratcheting behavior with a high mean stress reduces fatigue life of rail steel by comparing fatigue lives under stress cycling with those under strain cycling. Research findings are helpful to evaluate fatigue life of U75V rail steel in the railways with passenger and freight traffic.

scholarly journals High Cycle Fatigue Appearance of 10wt% cr steel and Dissimilar Metal Weld

2021 ◽  
Vol 9 (VI) ◽  
pp. 2185-2202
Author(s):  
Hilal Ahmad Shah
Keyword(s):  
Fatigue Life ◽  
High Cycle Fatigue ◽  
Stress Amplitude ◽  
Cycle Fatigue ◽  
Crack Initiation And Propagation ◽  
R Ratio ◽  
Initiation And Propagation ◽  
Different Temperatures ◽  
Fracture Surface Analysis ◽  
Metal Weld

The present study deals with the high cycle fatigue (HCF) behavior of a ten wt% Cr steel at ambient also as high temperatures (300–853 K). S–N curves were created at unlike temperatures using an R-ratio of −1. Outcome of mean stress was established over and done with Haigh diagram at 853 K using different R-values. Fatigue life was found to decrease with upsurge in test temperature and stress amplitude. Fatigue life was attempted using Basquin equation. Detailed fracture surface analysis was performed to study the crack initiation and propagation modes towards empathetic the mechanisms of failure at different temperatures.

Effect of Plasticity on Fatigue Life of Welded Nuclear Component With Local Brittle Zone

2003 ◽  
Author(s):  
Jong-Sung Kim ◽  
Se-Hwan Lee ◽  
Tae-Eun Jin
Keyword(s):  
Fatigue Life ◽  
Tensile Properties ◽  
Stress Amplitude ◽  
Low Alloy Steels ◽  
The Finite Element Method ◽  
Fatigue Lifetime ◽  
Nuclear Component ◽  
Alloy Steels ◽  
Brittle Zone ◽  
Produce Strain

The local brittle zone (LBZ), which has lower tensile properties as well as lower fracture toughness than base metal and weldment, can occur on the heat affected zone (HAZ) of some nuclear components made of low alloy steels due to the carbide coarsening by multi-pass welding and post-weld heat treatment. These variations of material strengths across the welds due to the LBZ can produce strain concentrations when the stress amplitude is large enough to cause cyclic plastic flow. But, it is difficult to find the previous researches about a relation between the fatigue life of LBZ on real nuclear components and plasticity. So, in this study, the microstructures and tensile properties of HAZ on nuclear components are predicted by using the semi-analytical method, and the fatigue lifetimes of welds on nuclear components with the LBZ are evaluated by the finite element method considering the local plasticity and the variations of tensile properties, and the fatigue analysis procedure of ASME B&PV Code Sec.III. Finally, the effect of LBZ on nuclear components on fatigue lifetime is reviewed.

Creep Behavior of a Solder Paste With Bi Addition

2017 ◽  
Author(s):  
Pedro E. Ribeiro ◽  
Delfim F. Soares ◽  
Maria F. Cerqueira ◽  
Senhorinha F. Teixeira ◽  
Daniel A. Barros ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Solder Joint ◽  
Mechanical Performance ◽  
Creep Behaviour ◽  
Real Life ◽  
Production Costs ◽  
Solder Paste ◽  
Creep Tests ◽  
Pcb Assembly ◽  
Solder Joint Fatigue

A common failure mode of electronic PCB’s is the appearance of cold solder joints between the component and PCB, during product life. This phenomenon is related to solder joint fatigue and is attributed mainly to the mismatch of the coefficients of thermal expansion (CTE) of component-solder-PCB assembly. Although some experiments show that newer lead-free tin-silver-copper (Sn-Ag-Cu, or SAC) solders perform better than the older SnPb ones, with today’s solder joint thickness decreasing and increasing working temperatures, among others, the stresses and strains due to temperature changes are growing, leading to limited fatigue life of the products. As fatigue life decreases with increasing plastic strain, creep occurrence should have significant impact, especially during thermal cycles. In order to improve mechanical properties, but also as an attempt to reduce maximum reflow cycle temperatures due to component damage and production costs, various SAC solder alloying additives are being considered to use in industrial production facilities. Solder paste producers are proposing new products based on new solder paste formulations, but the real life effects on thermo-mechanical performance aren’t well known at the moment. In this paper a dynamic mechanical analyser (DMA) is used to study the influence of Bismuth (Bi) addition, up to 5 wt %, on SAC405 solder paste, in terms of creep behaviour. Creep tests were made on three-point-bending configuration, isothermally at 30 °C, 50 °C and 75 °C, and three different stresses of 3, 5 and 9 MPa. The results shown not only a significant Bi concentration influence on creep behaviour but also a noticeable temperature dependence.

scholarly journals A Fatigue Life Prediction Model Based on Modified Resolved Shear Stress for Nickel-Based Single Crystal Superalloys

Metals ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 180 ◽  
Author(s):  
Jialiang Wang ◽  
Dasheng Wei ◽  
Yanrong Wang ◽  
Xianghua Jiang
Keyword(s):  
Shear Stress ◽  
Fatigue Life ◽  
Prediction Model ◽  
Single Crystal ◽  
Life Prediction ◽  
Stress Amplitude ◽  
Damage Parameter ◽  
Fatigue Life Prediction ◽  
Model Based ◽  
Life Prediction Model

In this paper, the viewpoint that maximum resolved shear stress corresponding to the two slip systems in a nickel-based single crystal high-temperature fatigue experiment works together was put forward. A nickel-based single crystal fatigue life prediction model based on modified resolved shear stress amplitude was proposed. For the four groups of fatigue data, eight classical fatigue life prediction models were compared with the model proposed in this paper. Strain parameter is poor in fatigue life prediction as a damage parameter. The life prediction results of the fatigue life prediction model with stress amplitude as the damage parameter, the fatigue life prediction model with maximum resolved shear stress in 30 slip directions as the damage parameter, and the McDiarmid (McD) model, are better. The model proposed in this paper has higher life prediction accuracy.

scholarly journals Flexural Fatigue Performance of Steel Fiber Reinforced Expanded-Shales Lightweight Concrete Superposed Beams with Initial Static-Load Cracks

Materials ◽  
2019 ◽  
Vol 12 (19) ◽  
pp. 3261
Author(s):  
Fulai Qu ◽  
Changyong Li ◽  
Chao Peng ◽  
Xinxin Ding ◽  
Xiaowu Hu ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Static Load ◽  
Steel Fiber ◽  
Lightweight Concrete ◽  
Volume Fraction ◽  
Stress Amplitude ◽  
Flexural Stiffness ◽  
Compression Zone ◽  
Fatigue Load ◽  
Upper Limit

Concerning the structural applications of steel fiber reinforced expanded-shales lightweight concrete (SFRELC), the present study focuses on the flexural fatigue performance of SFRELC superposed beams with initial static-load cracks. Nine SFRELC superposed beams were fabricated with the SFRELC depth varying from 50% to 70% of the whole sectional depth, and the volume fraction of steel fiber ranged from 0.8% to 1.6%. The fatigue load exerted on the beams was a constant amplitude sinusoid with a frequency of 10 Hz and a fatigue characteristic value of 0.10; the upper limit was taken as the load corresponded to the maximum crack width of 0.20 mm at the barycenter of the longitudinal rebars. The results showed that with the increase of SFRELC depth and the volume fraction of steel fiber, the fatigue life of the test beams was prolonged with three altered failure modes due to the crush of conventional concrete in the compression zone and/or the fracture of the tensile rebar; the failure pattern could be more ductile by the prevention of fatigue fracture by the longitudinal tensile rebar when the volume fraction of steel fiber was 1.6% and the reduction of crack growth and concrete strain in the compression zone; the fatigue life of test beams was sensitive to the upper-limit of the fatigue load, a short fatigue life appeared from the higher stress level and larger stress amplitude of the longitudinal rebar due to the higher upper-limit of the fatigue load. The methods for predicting the stress level, the stress amplitude of the longitudinal tensile rebar, and the degenerated flexural stiffness of SFRELC superposed beams with fatigue life are proposed. With the optimal composites of the SFRELC depth ratio and the volume fraction of steel fiber, the controllable failure of reinforced SFRELC superposed beams could be a good prospect with the trend curves of fatigue flexural stiffness.

Relationship Between Fatigue Life Distribution, Notch Configuration, and S-N Curve of a 2024-T4 Aluminum Alloy

1985 ◽  
Vol 107 (3) ◽  
pp. 214-220 ◽  
Author(s):  
T. Shimokawa ◽  
Y. Hamaguchi
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Life ◽  
Stress Amplitude ◽  
Fatigue Tests ◽  
Test Results ◽  
Notched Specimens ◽  
Wide Range ◽  
Life Distributions ◽  
The Relationship ◽  
Test Stress

The objective of this study is to identify the most closely related variable to the distribution of fatigue life in unnotched and three kinds of notched 2024-T4 aluminum alloy specimens. Carefully designed fatigue tests under a constant temperature and humidity condition provided fatigue life distributions over a wide range of stress amplitude. This study used about 1000 specimens. On the basis of the test results, the dependence of the scatter in fatigue life on notch configuration, the period to crack initiation, the level of stress amplitude, the median fatigue life, and the slope of the median S-N curve is investigated, and the relationship between the distributional form of fatigue life and the shape of the median S-N curve is discussed. It is concluded that the slope and shape of the median S-N curve in the vicinity of the test stress level are closely related to the scatter and distributional form of fatigue life respectively. This is common to the unnotched and three kinds of notched specimens. A variability hypothesis to correlate the median S-N curve with fatigue life distributions is examined.

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