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

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.

Investigation of the fatigue behavior of thermoplastic composites by load increase tests

2020 ◽  
pp. 002199832095452
Author(s):  
Andreas Baumann ◽  
Sebastian Backe ◽  
Joachim Hausmann
Keyword(s):  
Fatigue Behavior ◽  
Numerical Data ◽  
Fatigue Loading ◽  
Polyamide 6 ◽  
Heat Emission ◽  
Thermoplastic Composites ◽  
Failure Behavior ◽  
Glass Fiber Reinforced ◽  
The Matrix ◽  
Load Increase

Fatigue is one major load case in many structures for transport applications. New materials often lack the necessary data base for a fast application in cyclic loaded components due to time consuming testing series. The aim of this study is the evaluation of the load increase test as method to determine a possible fatigue limit of glass fiber reinforced polyamide 6. Under the working hypothesis that cracks are the main contributors for heat emission, the results show that the investigated material exhibits a different behavior in comparison to thermosets. Instead of crack formation experimental and numerical data indicate that the matrix relaxes under fatigue loading. This relaxation could potentially lead to crack prevention but might also result in the observed sudden failure behavior of the material. These findings suggest a totally different behavior of thermoplastic composites under fatigue loading.

Improving Creep-Fatigue Design Methodology for Advanced Ferritic-Martensitic Steels

2014 ◽  
Author(s):  
Meimei Li ◽  
William K. Soppet ◽  
Saurin Majumdar ◽  
Ken Natesan
Keyword(s):  
Design Methodology ◽  
Laboratory Data ◽  
Constitutive Models ◽  
Fatigue Loading ◽  
Cyclic Softening ◽  
Advanced Materials ◽  
Critical Element ◽  
Martensitic Steels ◽  
Fast Reactors ◽  
Creep Fatigue

Advanced materials are a critical element in the development of advanced sodium-cooled fast reactors. High temperature design methodology of advanced materials is an enabling reactor technology. Removal of unnecessary conservatism in design rules could lead to more flexibility in construction and operation of advanced sodium-cooled fast reactors. Developing mechanistic understanding and predictive models for long-term degradation phenomena such as creep-fatigue are essential to the extrapolation of accelerated laboratory data to reactor environments with high confidence, and to improve the American Society of Mechanical Engineers (ASME) code rules. This paper examines the cyclic softening and stress relaxation responses and associated plastic damage accumulation for Grade 91 ferritic-martensitic steel. Creep-fatigue experiments were conducted at 550°C in strain-controlled mode under various types of creep-fatigue loading conditions. Constitutive models were developed to describe the creep-fatigue interaction in G91.

scholarly journals Failure Mechanisms of Mechanically and Thermally Produced Holes in High-Strength Low-Alloy Steel Plates Subjected to Fatigue Loading

Metals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 318 ◽  
Author(s):  
Carlos Jiménez-Peña ◽  
Constantinos Goulas ◽  
Johannes Preußner ◽  
Dimitri Debruyne
Keyword(s):  
Yield Strength ◽  
Electron Backscatter Diffraction ◽  
Fatigue Behavior ◽  
Base Material ◽  
High Strength ◽  
Fatigue Loading ◽  
Offshore Structures ◽  
Load Level ◽  
Low Alloy Steels ◽  
Structural Applications

High-strength low-alloy steels (HSLA) are gaining popularity in structural applications in which weight reduction is of interest, such as heavy duty machinery, bridges, and offshore structures. Since the fatigue behavior of welds appears to be almost independent of the base material and displays little improvement when more resistant steel grades are employed, the use of bolted joints is an alternative joining technique which can lead to an increased fatigue performance of HSLA connections. Manufacturing a hole to allocate the fastener elements is an unavoidable step in bolted elements and it might induce defects and tensile residual stresses that could affect its fatigue behavior. This paper studies and compares several mechanical (punching, drilling, and waterjet-cut) and thermal (plasma and laser-cut) hole-making procedures in HSLA structural plates. A series of 63 uniaxial fatigue tests was completed, covering three HSLA grades produced by thermomechanically controlled process (TMCP) with yield strength ranging from 500 to 960 MPa. Samples were tested at single load level, which was considered representative in HSLA typical applications, according to the input received from end users. The manufactured holes were examined by means of optical and electron microscopy, 3D point measurement, micro hardness tests, X-ray diffraction, and electron backscatter diffraction (EBSD). The results give insight on cutting processes in HSLA and indicate how the fatigue failure is dominated by macro defects rather than by the steel grade. It was shown that the higher yield strength of the HSLA grades did not lead to a higher fatigue life. Best fatigue results were achieved with laser-cut specimens while punched samples withstood the lowest amount of cycles.

scholarly journals Fatigue Behavior of 3D Braided Composites Containing an Open-Hole

Polymers ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 2147
Author(s):  
Shuangqiang Liang ◽  
Qihong Zhou ◽  
Haiyang Mei ◽  
Ge Chen ◽  
Frank Ko
Keyword(s):  
Cross Section ◽  
Fatigue Behavior ◽  
Fatigue Loading ◽  
Fatigue Properties ◽  
Failure Behavior ◽  
Braided Composites ◽  
Damage Area ◽  
3D Braided Composites ◽  
Mechanical Performances ◽  
Braiding Angle

The static and dynamic mechanical performances of notched and un-notched 3D braided composites were studied. The effect of longitudinal laid-in yarn was investigated in comparison with low braiding angle composites. The specimens were fatigue tested for up to millions of cycles, and the residual strength of the samples that survived millions of cycles was tested. The cross-section of the 3D braided specimens was observed after fatigue loading. It was found that the static and fatigue properties of low angle 3D braided behaved better than longitudinally reinforced 3D braided composites. For failure behavior, pure braids contain damage better and show less damage area than the braids with longitudinal yarns under fatigue loading. More cracks occurred in the 3D braided specimen with axial yarn cross-section along the longitudinal and transverse direction.

A Continuum Damage Mechanics-Based Viscoplastic Model of Adapted Complexity for High-Temperature Creep–Fatigue Loading

2016 ◽  
Vol 138 (9) ◽  
Author(s):  
Weizhe Wang ◽  
Patrick Buhl ◽  
Andreas Klenk ◽  
Yingzheng Liu
Keyword(s):  
Damage Mechanics ◽  
Fatigue Behavior ◽  
Continuum Damage Mechanics ◽  
Fatigue Loading ◽  
Material Model ◽  
Material Behavior ◽  
Continuum Damage ◽  
Loading Test ◽  
Constitutive Material Model ◽  
Creep Fatigue

A continuum damage mechanics (CDM) based viscoplastic constitutive model is established in this study to describe the fully coupling of creep and fatigue behavior. The most significant improvement is the introduction of a continuum damage variable into the constitutive equations, instead of considering creep damage and fatigue damage separately. The CDM-based viscoplastic constitutive material model is implemented using a user-defined subroutine (UMAT). A standard specimen is used for carrying out uniaxial creep, fatigue, and creep–fatigue interaction tests to validate the material model. In addition, to further demonstrate the capability of the material model to predict the complex material behavior, a complex strain-control loading test is performed to validate the material model. The simulated and measured results are in good agreement at different temperatures and loadings, in particular for rapid cyclic softening behavior following crack initiation and propagation.

Creep-Fatigue Behavior of Grade 92 Steel and its Predictability

2011 ◽  
Author(s):  
Yukio Takahashi ◽  
David Gandy
Keyword(s):  
Base Metal ◽  
Creep Strength ◽  
Power Plants ◽  
Fatigue Behavior ◽  
Creep Damage ◽  
Primary Concern ◽  
Wide Range ◽  
Piping Systems ◽  
Creep Fatigue ◽  
Grade 92 Steel

Grade 92 steel is a class of the Creep Strength-Enhanced Ferritic (CSEF) steels developed for use in boilers and piping systems of ultra-supercritical steam fossil power plants. Although creep strength is a primary concern, consideration of the interaction of creep and fatigue damage is also important in evaluating the integrity of components as they will experience a range of cyclic loading. Although some studies have already been made on creep-fatigue behavior of this steel, test data under the conditions of creep damage dominance more relevant to plant evaluation, need to be supplemented. Girth welds often constitute critical locations dominating the integrity of piping systems and their creep-fatigue behavior is also of significant importance. Such a situation prompted the authors to initiate a study aiming at development of an extensive database on creep-fatigue behavior of base metal and welded joints of Grade 92 steel and establishment of an appropriate life estimation procedure. For the period of one and half year, a number of creep-fatigue data have been obtained on the base metal and cross-weld specimens at a wide range of loading conditions. Superiority of the energy-based approach to the conventional time fraction or ductility exhaustion approach for predicting creep-fatigue life was confirmed by their application to these creep-fatigue tests.

Creep-Fatigue Behavior in Ferritic-Martensitic Steels

2011 ◽  
Author(s):  
Meimei Li ◽  
Saurin Majumdar ◽  
Ken Natesan
Keyword(s):  
High Temperature ◽  
Stress Relaxation ◽  
Fatigue Behavior ◽  
Hold Time ◽  
Creep Damage ◽  
Cyclic Softening ◽  
Relaxation Response ◽  
Martensitic Steels ◽  
Softening Effect ◽  
Creep Fatigue

Ferritic-martensitic steels are the lead structural materials for next-generation nuclear energy systems. Due to increased operating temperatures required in advanced high-temperature reactor concepts, the high temperature performance of structural alloys and reliable high temperature structural design methodology have become increasingly urgent issues. Ferritic-martensitic steels experience significant cyclic softening at high temperatures, and this cyclic softening behavior affects consecutive stress relaxation response during hold time under creep-fatigue loading. It is found that the stress relaxation response during hold of the mod.9Cr-1Mo steel can be accurately described by a stress relaxation model. The creep damage associated with the stress relaxation during hold time can then be accurately calculated using the stress relaxation data and creep rupture data. It is shown that the unit creep damage per cycle in mod.9Cr-1Mo steel decreases considerably with increasing number of cycles due to cyclic softening, and the creep damage is sensitive to the initial stress of stress relaxation. Proper evaluation of the creep-fatigue damage in mod.9Cr-1Mo steel must consider the cyclic softening effect and its associated variations in creep damage from stress relaxation during the hold time.

Application Concepts and Experimental Validation of Constitutive Material Models for Creep-Fatigue Assessment of Components

2019 ◽  
Author(s):  
Christian Kontermann ◽  
Stefan Linn ◽  
Matthias Oechsner
Keyword(s):  
Model Development ◽  
Fatigue Loading ◽  
Material Model ◽  
Equation System ◽  
Current Status ◽  
Viscoplastic Material ◽  
Material Models ◽  
Constitutive Material Model ◽  
Creep Fatigue ◽  
Constitutive Material

Abstract The possibility to use real operational data as an input for lifetime assessment methods is a key requirement in terms of both service applications as well as within the design of components by underlying specific service relevant scenarios. To address this, so called “Constitutive Viscoplastic Material Models” have been developed which represent a more generalized alternative for assessing turbo machinery components which undergo an irregular creep-fatigue loading. Based on several experimental and theory related national research programs, performed within the German working group W10 in the last years, the current status of the model development and the performance potentials are summarized in this paper. Within the first part, the general and developed model structure of one candidate material model is introduced by discussing different aspects of the equation system together with the specific practical related aspects. Secondly, the validation of this constitutive material model is shown by comparing the model results with a set of conducted complex experiments, like ansiothermal service like experiments performed on smooth, notched and biaxially loaded cruciform test samples. As the third focus, the applicability and the potential of using such a model for assessing real components will be discussed e.g. by introducing extrapolation or cycle jump concepts which allows to majorly reduce the calculation time without decreasing the result accuracy significantly. Finally, future potentials will be introduced with the goal to use such sophisticated models to train meta-models and finally allow for a machine-learning based on-site and service related on-line component assessment.

scholarly journals On Bond-slip of EB-FRP/Concrete Interface in Shear Under Fatigue Loading: Review and Synthesis of Experimental Studies and Models

2022 ◽  
Vol 11 (1) ◽  
pp. 1-19
Author(s):  
Abbas Fathi ◽  
Georges El-Saikaly ◽  
Omar Chaallal
Keyword(s):  
Structural Damage ◽  
Fatigue Behavior ◽  
Experimental Studies ◽  
Fatigue Loading ◽  
Cyclic Fatigue ◽  
Design Guidelines ◽  
Rc Structures ◽  
Bond Slip ◽  
Wide Range ◽  
Concrete Interface

Reinforced concrete (RC) structures subjected to cyclic fatigue loading are prone to progressive damage. Among the types of structural damage, those leading to shear deficiencies can result in sudden rupture of structures without warning. Hence, RC structures deficient in shear urgently need retrofitting. The use of externally bonded (EB) fiber-reinforced polymer (FRP) composites presents many advantages and is a very promising technology for shear strengthening of RC structures. This paper encompasses a wide range of research findings related to the interaction between concrete and FRP under fatigue loading. The behavior of the bond between FRP and concrete plays a major role in the failure mode of FRP shear-strengthened structures especially under fatigue. Therefore, it is of interest to characterize the FRP/concrete interaction using appropriate models with respect to the influencing parameters. The paper will first discuss existing design guidelines and considerations related to the fatigue behavior of RC structures. A thorough review of available literature on EB-FRP/concrete bond in shear under cyclic fatigue loading will then be presented, with a focus on proposed bond-slip models and finite element studies of the FRP/concrete interface under fatigue loading.

Sign in / Sign up

Export Citation Format

Share Document