Comparison of local strains at the notch root between FEM analysis and experimental strain measurement in creep-fatigue condition.

AbstractTo increase learning success in surgical training, physical simulators are supplemented by measurement technology to generate and record objective feedback and error detection. An opportunity to detect fractures following hip stem implantation early can be measurement of occurring strains on bone surface. These strains can be determined while using strain gauges, digital image correlation (DIC) or photoelasticity. In this research strain gauges and DIC were compared regarding their suitability as strain measurement tools for use in physical simulators. Therefore a testing method was described to replicate the implantation of a hip stem. Testing devices modelled on a realistic prosthesis were pressed into prepared porcine femora in a two-step procedure with a material testing machine. The local strains occurring on bone surface were determined using an optical measurement system for DIC and strain gauges. The initial fractures in the tested femora are located medial-anterior in most cases (73,6%). With increasing indentation depth of the test device, the strains on bone surface increase. Comparing the local strains determined by DIC and strain gauges consistencies in curves are noticeable. Maximal determined strains before fracturing amount to 0,69% with strain gauges and 0,75% with DIC. In the range of the fracture gap, strain gradients are determined by using DIC. However the detected surfaces are of low quality caused by gaps and motion artefacts. The results show strains on bone surfaces for early fracture detection are measurable with strain gauges and DIC. DIC is assessed as less suitable compared to strain gauges. Furthermore strain gauges have greater level of integration and economic efficiency, so they are preferred the use in surgical training simulators.

Download Full-text

Biophysical stress analysis of restored teeth: experimental strain measurement

Dental Materials ◽

10.1016/s0109-5641(88)80087-3 ◽

1988 ◽

Vol 4 (1) ◽

pp. 41-48 ◽

Cited By ~ 56

Author(s):

D.L. Morin ◽

W.H. Douglas ◽

M. Cross ◽

R. Delong

Keyword(s):

Stress Analysis ◽

Strain Measurement ◽

Experimental Strain

Download Full-text

Notch-Strengthening Phenomenon Under Creep-Fatigue Loading Conditions

Journal of Pressure Vessel Technology ◽

10.1115/1.556140 ◽

1999 ◽

Vol 122 (1) ◽

pp. 15-21 ◽

Cited By ~ 3

Author(s):

N. Merah

Keyword(s):

Experimental Data ◽

Stress Relaxation ◽

Notch Root ◽

Hold Time ◽

Local Stress ◽

Frequency Effect ◽

Strengthening Effect ◽

Strain Accumulation ◽

Element Analysis ◽

Creep Fatigue

A study of the notch and frequency effects on fatigue life at high temperature is carried out using notched and unnotched plate specimens of SS 304 under stress-controlled testing conditions. Analysis of the σ-Nf results obtained at 600°C under fatigue and creep-fatigue conditions allowed the generalization of the σ-Nf-Kt relation proposed in an earlier study. Examinations of the experimental data with hold-time testing suggested that in these conditions, the frequency effect should be incorporated in the relationship. Results obtained from the modified relation are in agreement with the experimental data, within a factor of two. Finite element analysis was carried out to determine the state of stresses and strains at the notch root by simulating four creep-fatigue cycles. The computed results indicated that, under zero-to-tension cyclic loading with controlled nominal stress, the maximum local stress at the notch root relaxes; this results in a minimum local stress in compression, and as a consequence, the mean local stress is significantly reduced. The stress relaxation as well as the creep strain accumulation were found to occur only in the vicinity of the notch (within 0.75 mm). The numerical results concerning the local stress relaxation and the time-dependent strain accumulation are used to explain the notch-strengthening effect on life observed in the present study. [S0094-9930(00)00401-7]

Download Full-text

Life Prediction for Notched Components in Nonproportional Low Cycle Fatigue: Experiment and FEM Analysis

Pressure Vessel and Piping Codes and Standards ◽

10.1115/pvp2004-2670 ◽

2004 ◽

Author(s):

Masao Sakane ◽

Tsuneo Itoh ◽

Tomoshige Susaki ◽

Yoshiyasu Kawazoe

Keyword(s):

Crack Initiation ◽

Linear Models ◽

Low Cycle Fatigue ◽

Notch Root ◽

Fem Analysis ◽

Local Strain ◽

304 Stainless Steel ◽

Cycle Fatigue ◽

Notched Specimens ◽

Strain Paths

This paper studies the low cycle fatigue of circumferential notched specimens of type 304 stainless steel in nonproportional loading. Strain controlled tension-torsion low cycle fatigue tests were carried out using the notched specimens under 15 strain paths. Crack initiation lives detected by a d.c. potential method were discussed in relation to the strain concentration factors and strain histories. Finite element analyses were carried out for evaluating the local strain at the notch root using elastic-perfectly plastic and bi-linear models. The maximum principal strain and nonproportional strain ranges conservatively estimated the crack initiation lives of the notched specimens.

Download Full-text

Low cycle fatigue behavior of circumferentially notched specimens made of modified 9Cr–1Mo steel at elevated temperature

International Review of Applied Sciences and Engineering ◽

10.1556/1848.2021.00305 ◽

2021 ◽

Vol 13 (1) ◽

pp. 54-62

Author(s):

Ikram Abarkan ◽

Abdellatif Khamlichi ◽

Rabee Shamass

Keyword(s):

Fatigue Life ◽

Elevated Temperature ◽

Applied Stress ◽

Stress Amplitude ◽

Low Cycle Fatigue ◽

Notch Root ◽

Reliable Determination ◽

Local Strains ◽

Analytical Approximations ◽

Neuber's Rule

Abstract During service, notched designed components such as steam generators in the nuclear power plant usually experience fatigue damage at elevated temperatures, due to the repeated cyclic loadings during start-up and shut-down operations. Under such extreme conditions, the durability of these components is highly-affected. Besides, to assess the fatigue life of these components, a reliable determination of the local stress-strain at the notch-tips is needed. In this work, the maximum strains of circumferentially notched cylindrical specimens were calculated using the most commonly known analytical methods, namely Neuber's rule, modified Neuber's rule, Glinka's rule, and linear rule, with notch root radius of 1.25, 2.5, and 5 mm, made of modified 9Cr–1Mo steel at 550 °C, and subjected to nominal stress amplitudes of ±124.95, ±149.95, and ±174.95 MPa. The calculated local strains were compared to those obtained from Finite Element Analysis (FEA). It was found that all the analytical approximations provided unreliable local strains at the notch-tips, resulting in an overestimation or underestimation of the fatigue life. Therefore, a mathematical model that predicts the fatigue lives for 9Cr–1Mo steel at elevated temperature was proposed in terms of the applied stress amplitude and the fatigue stress concentration factor. The calculated fatigue lifetimes using the proposed model are found to be in good agreement with those obtained experimentally from the literature with relative errors, when the applied stress amplitude is ±149.95 MPa, are of 1.97%,–8.67%, and 13.54%, for notch root radii of 1.25, 2.5, and 5 mm, respectively.

Download Full-text

Damage Assessment of Similar Martensitic Welds Under Creep, Fatigue and Creep-Fatigue Loading

Volume 6: Materials and Fabrication ◽

10.1115/pvp2020-21497 ◽

2020 ◽

Author(s):

Thorben Bender ◽

Andreas Klenk ◽

Stefan Weihe

Keyword(s):

Base Metal ◽

Fatigue Behavior ◽

Base Material ◽

Fatigue Loading ◽

Design Guidelines ◽

Failure Behavior ◽

Martensitic Steels ◽

Viscoplastic Material ◽

Local Strains ◽

Creep Fatigue

Abstract For the assessment of welds under high-temperature conditions in the creep or creep-fatigue regimes, the knowledge on the damage location and its temporal evolution are of high importance. The failure behavior of similar welds of ferritic-martensitic steels in the creep regime is well known. For creep-fatigue loading, the behavior of welds is still subject to research but it seems that the heat affected zone (HAZ) limits the lifetime of welded components as well. This local failure behavior is not reflected in design guidelines using weld reduction factors or in typical assessment approaches. The evaluation of local strains and stresses in the HAZ is unavoidable. For the improvement of design and inspection guidelines, a more detailed consideration of weld behavior is of interest. In this paper, an overview of current developments in the assessment of welds under creep, fatigue, and creep-fatigue loading conditions is given. An assessment approach for creep damage and failure, including the prediction of rupture time and location, is presented. The assessment is based on numerical analyses considering the different behavior of base material and HAZ represented by three different subzones. The approach is validated with the simulation of a uniaxial cross weld, creep crack, and component tests. Whereas the creep behavior of the HAZ compared to base metal is quite well known, there is only little knowledge of their fatigue behavior. Using a set of fatigue tests on HAZ, base metal specimens and cross weld specimens, the influence of fatigue and creep-fatigue loading on the lifetime and failure location of a weld will be discussed. For the numerical simulations, a viscoplastic material law of Chaboche type is used and an evaluation of the local strains in the HAZ allows an attempt to explain the observed failure locations.

Download Full-text

Study on Creep-Fatigue Damage Evaluation for Boiler Weldment Parts

Journal of Pressure Vessel Technology ◽

10.1115/1.1339979 ◽

2000 ◽

Vol 123 (1) ◽

pp. 105-111 ◽

Cited By ~ 4

Author(s):

Takashi Ogata ◽

Masatsugu Yaguchi

Keyword(s):

Weld Joint ◽

Creep Damage ◽

Fem Analysis ◽

Fatigue Tests ◽

Type Iv ◽

Fine Grain ◽

Creep Fatigue ◽

Damage Accumulation Model ◽

Type Iv Cracking ◽

Failure Life

Creep-fatigue tests on the heat-affected zone(HAZ) simulated materials, base metal, weld metal and weld joint of 2.25Cr-1Mo steel, and elastic-plastic and creep FEM analysis for the weld joint were conducted. It was found from the comparison between experimental evidences and the analytical results that “Type IV” cracking was caused by two major reasons. One is accumulation of creep strain during strain hold in the fine-grain region is larger than that in other regions, suggesting progress of creep damage in the fine-grain region prior to other regions. The other is existence of triaxial tensile stress field within the fine-grain region caused reduction of failure ductility. Crack initiation portion and failure life under the creep-fatigue test could be well predicted by the nonlinear damage accumulation model based on the FEM analysis results.

Download Full-text

Measurement of dynamic and static strain in small specimens at elevated temperatures

Journal of Strain Analysis ◽

10.1243/03093247v092130 ◽

1974 ◽

Vol 9 (2) ◽

pp. 130-134

Author(s):

G Sumner

Keyword(s):

Strain Measurement ◽

Elevated Temperatures ◽

Low Frequency ◽

Displacement Transducer ◽

Gauge Length ◽

Reference Points ◽

Dynamic Strain ◽

Optical Displacement ◽

Creep Fatigue ◽

Displacement Transducers

A method of strain measurement in small specimens is described which involves measurement of strain in terms of the net displacement of reference points within the specimen ends rather than on the gauge length. The reference points are the bottoms of axial holes drilled into the specimen heads. The method has been developed for high-frequency dynamic-strain measurement using a novel electro-optical displacement transducer and for low-frequency creep-fatigue work using conventional displacement transducers.

Download Full-text

Notch Root Displacement (NRD) Approach to Predict Crack Initiation Life of Notched Specimen in High-Temperature Multiaxial Low Cycle Fatigue

Journal of Engineering Materials and Technology ◽

10.1115/1.2903353 ◽

1990 ◽

Vol 112 (4) ◽

pp. 429-434 ◽

Cited By ~ 6

Author(s):

Hiroshi Umeda ◽

Masao Sakane ◽

Masateru Ohmani

Keyword(s):

High Temperature ◽

Crack Initiation ◽

Low Cycle Fatigue ◽

Notch Root ◽

Three Dimensional ◽

Fem Analysis ◽

Cycle Fatigue ◽

Notched Specimen ◽

Crack Initiation Life ◽

Three Dimensional Finite Element

This paper describes the notch root displacement (NRD) approach to assess the crack initiation life of notched specimens in high-temperature multiaxial low cycle fatigue. Two and three-dimensional finite element method (FEM) analyses were made to estimate the local displacement at the notch root in tension, torsion, and combined tension/torsion. From the FEM analysis, a simple equation which expresses the intensity of the notch root displacement was derived and it was applied to the experimental data. The equation well correlates the crack initiation life of the notched specimen in high-temperature multiaxial low cycle fatigue.

Download Full-text