A Direct Method on the Evaluation of Cyclic Steady State of Structures With Creep Effect

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
Haofeng Chen ◽  
Weihang Chen ◽  
James Ure
Keyword(s):  
Fatigue Damage ◽  
Mechanical Load ◽  
Direct Method ◽  
Load Condition ◽  
Hysteresis Loops ◽  
Strain Range ◽  
Cyclic Behavior ◽  
Direct Evaluation ◽  
Plastic Strain Range ◽  
Creep Fatigue

This paper describes a new extension of the linear matching method (LMM) for the direct evaluation of cyclic behavior with creep effects of structures subjected to a general load condition in the steady cyclic state, with the new implementation of the cyclic hardening model and time hardening creep constitutive model. A benchmark example of a Bree cylinder and a more complicated three-dimensional (3D) plate with a center hole subjected to cyclic thermal load and constant mechanical load are analyzed to verify the applicability of the new LMM to deal with the creep fatigue damage. For both examples, the stabilized cyclic responses for different loading conditions and dwell time periods are obtained and validated. The effects of creep behavior on the cyclic responses are investigated. The new LMM procedure provides a general purpose technique, which is able to generate both the closed and nonclosed hysteresis loops depending upon the applied load condition, providing details of creep strain and plastic strain range for creep and fatigue damage assessments with creep fatigue interaction.

A Direct Method on the Evaluation of Cyclic Behaviour With Creep Effect

2012 ◽  
Author(s):  
Haofeng Chen ◽  
Weihang Chen ◽  
James Ure
Keyword(s):  
Plastic Strain ◽  
Creep Strain ◽  
Fatigue Damage ◽  
Mechanical Load ◽  
Direct Method ◽  
Load Condition ◽  
Strain Range ◽  
Plastic Strain Range ◽  
Cyclic Behaviour ◽  
Creep Fatigue

This paper describes a new Linear Matching Method (LMM) technique for the direct evaluation of cyclic behaviour with creep effects of structures subjected to a general load condition in the steady cyclic state. The creep strain and plastic strain range for use in creep damage and fatigue assessments, respectively, are obtained. A benchmark example of a Bree cylinder subjected to cyclic thermal load and constant mechanical load is analysed to verify the applicability of the new LMM to deal with the creep fatigue damage. The cyclic responses for different loading conditions and dwell time periods within the Bree boundary are obtained. To demonstrate the efficiency and effectiveness of the method for more complex structures, a 3D holed plate subjected to cyclic thermal loads and constant axial tension is analysed. The results of both examples show that with the presence of creep the cyclic responses change significantly. The new LMM procedure provides a general purpose technique for the evaluation of cyclic behaviour, the plastic strain range and creep strain for the creep fatigue damage assessment with creep fatigue interaction.

scholarly journals On Creep Fatigue Interaction of Components at Elevated Temperature

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Daniele Barbera ◽  
Haofeng Chen ◽  
Yinghua Liu
Keyword(s):  
High Temperature ◽  
Mechanical Load ◽  
Direct Method ◽  
Bending Moment ◽  
Strain Range ◽  
Cyclic Plasticity ◽  
Element Analysis ◽  
Total Strain Range ◽  
Creep Fatigue ◽  
A Direct Method

The accurate assessment of creep–fatigue interaction is an important issue for industrial components operating with large cyclic thermal and mechanical loads. An extensive review of different aspects of creep fatigue interaction is proposed in this paper. The introduction of a high temperature creep dwell within the loading cycle has relevant impact on the structural behavior. Different mechanisms can occur, including the cyclically enhanced creep, the creep enhanced plasticity and creep ratchetting due to the creep fatigue interaction. A series of crucial parameters for crack initiation assessment can be identified, such as the start of dwell stress, the creep strain, and the total strain range. A comparison between the ASME NH and R5 is proposed, and the principal differences in calculating the aforementioned parameters are outlined. The linear matching method (LMM) framework is also presented and reviewed, as a direct method capable of calculating these parameters and assessing also the steady state cycle response due to creep and cyclic plasticity interaction. Two numerical examples are presented, the first one is a cruciform weldment subjected to cyclic bending moment and uniform high temperature with different dwell times. The second numerical example considers creep fatigue response on a long fiber reinforced metal matrix composite (MMC), which is subjected to a cycling uniform thermal field and a constant transverse mechanical load. All the results demonstrate that the LMM is capable of providing accurate solutions, and also relaxing the conservatisms of the design codes. Furthermore, as a direct method, it is more efficient than standard inelastic incremental finite element analysis.

A Direct Method on the Evaluation of Ratchet Limit

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Haofeng Chen ◽  
Alan R. S. Ponter
Keyword(s):  
Cyclic Load ◽  
Mechanical Load ◽  
Low Cycle Fatigue ◽  
Direct Method ◽  
Numerical Technique ◽  
Load Condition ◽  
Numerical Procedure ◽  
Constant Load ◽  
Inelastic Analysis ◽  
Additional Constant

This paper describes a new linear matching method (LMM) technique for the direct evaluation of the ratchet limit of a structure subjected to a general cyclic load condition, which can be decomposed into cyclic and constant components. The cyclic load history considered in this paper contains multiload extremes to include most complicated practical applications. The numerical procedure uses the LMM state-of-the-art numerical technique to obtain a stable cyclic state of component, followed by a LMM shakedown analysis, to calculate the maximum constant load, i.e., the ratchet limit, which indicates the load carrying capacity of the structure subjected to a cyclic load condition to withstand an additional constant load. This approach is particularly useful in conjunction with the evaluation of the stable cyclic response, which produces the cyclic stresses, residual stresses, and plastic strain ranges for the low cycle fatigue assessment. A benchmark example of a holed plate under the combined action of cyclic thermal load and constant mechanical load is presented to verify the applicability of the new ratchet limit method through a comparison with published results by a simplified method assuming a cyclic load with two extremes. To demonstrate the efficiency and effectiveness of the method for a complicated cyclic load condition with multiload extremes, a composite thick cylinder with a radial opening subjected to cyclic thermal loads and a constant internal pressure is analyzed using the proposed ratchet limit method. Further verification by the ABAQUS step-by-step inelastic analysis demonstrates that the proposed new method provides a general-purpose technique for the evaluation of the ratchet limit and has both the advantages of programming methods and the capacity to be implemented easily within a commercial finite element code Abaqus.

Creep Fatigue Damage Assessment of V-Butt Weld Pipe With an Extended Direct Steady Cycle Analysis

2018 ◽  
Author(s):  
Manu Puliyaneth ◽  
Haofeng Chen ◽  
Weiling Luan
Keyword(s):  
Fatigue Damage ◽  
Power Plants ◽  
Mechanical Load ◽  
Axial Stress ◽  
Load Level ◽  
Cyclic Plasticity ◽  
Butt Weld ◽  
Creep Fatigue ◽  
Welded Pipe ◽  
The Impact

One of the methods to increase the efficiency of power plants is by increasing their operating temperature, this can lead to various damage mechanisms due to creep-cyclic plasticity interactions such as creep ratcheting, cyclically enhanced creep and creep enhanced plasticity. In the presence of welds, their assessments are complicated due to the presence of different material zones, namely parent metal, weld metal and heat affected zone which exhibit different properties. This paper aims at investigating the creep-fatigue damage of a V-butt welded pipe under a constant mechanical load and a cyclic temperature load, considering full interaction between creep and cyclic plasticity using the extended Direct Steady Cycle Analysis (eDSCA) within the Linear Matching Method Framework (LMMF). The impact of applied load level and creep dwell on the failure mechanism and location is investigated. Influence of hoop to axial stress ratio and groove angle is studied comprehensively by choosing ranges covering majority of common pipe configurations. Further validation of results is carried out by using detailed step-by-step inelastic analyses in ABAQUS, thereby demonstrating the accuracy and efficiency of LMM eDSCA in predicating the remaining life of multi-material components such as a welded pipe, combining with appropriate creep and fatigue damage models.

The Creep-Fatigue Evaluation Method for Intermediate Hold Conditions: Proposal and Validation

2011 ◽  
Author(s):  
Satoshi Okajima ◽  
Nobuchika Kawasaki ◽  
Shoichi Kato ◽  
Naoto Kasahara
Keyword(s):  
Initial Stress ◽  
Fatigue Damage ◽  
Evaluation Method ◽  
Strain Range ◽  
Creep Damage ◽  
Fatigue Tests ◽  
Reactor Vessel ◽  
Liquid Sodium ◽  
Improved Method ◽  
Creep Fatigue

In this paper, for the application to the Japan Sodium-cooled Fast Reactor, JSFR, the creep-fatigue damage evaluation method is improved to consider the intermediate holding condition. The improved method is validated through both of the uni-axial and the structure model creep-fatigue tests. In these validations, the target material is 316FR steel, which is planned to use for the reactor vessel. The reactor vessel portion near the liquid sodium surface is one of the most probable points where the creep-fatigue damage is considerable. Because of the relaxation of the temperature gradient, the steady operation stress on the portion near the liquid sodium surface is less than the maximum stress in the transient. In the conventional method, in order to evaluate the creep damage conservatively, the maximum tensile value in the thermal stress transient cycle is used as the initial stress. The improved method evaluates the creep damage using the lower initial stress than the conventional method, while it has the rational margin. For the validation of the improved method, uni-axial creep-fatigue tests and structure model tests are carried out. A series of uni-axial creep-fatigue tests was carried out in the following conditions: 600 degree C testing temperature, 1% total strain range, 1 hour holding time, vacuum or air environments, and the various holding position. While the test environment affects the fatigue damage, it didn’t have significant effect on the creep damage. In the cases with high holding position, the creep damages were evaluated based on the given initial stress with high precision. In the other cases, by the assumption of the steady-stress existence, the rational margin is given for the evaluation. Furthermore, in the design stage, the evaluated creep-fatigue damage has enough margins derived from the conservative evaluation of the initial stress. The structural tests modeled the movement of the liquid sodium surface in the start-up and the shut-down stages, and the relaxation of the temperature gradient in the operation stage. In these tests, the temperature distribution was given by coolant water and an external high-frequency heating coil for the cylindrical specimen, and moved in the axial direction. In addition, the primary stress, which was caused by the weight of the reactor vessel, was given by the screw jack. As a result, using the strain range evaluated by the elastic analysis, the improved method evaluated the crack initiation life due to the creep-fatigue damage with the sufficient safety margin. In the case when the strain range was evaluated by the elastic-plastic analysis, the method predicted the crack initiation life with the good precision. While the evaluation of the crack penetration life was possible, further examination was desired for the precision improvement.

Low Cycle Fatigue Behavior of a Near-α Ti Alloy Containing Rare Earth Nd

2005 ◽  
Vol 475-479 ◽  
pp. 599-602
Author(s):  
Zhi Shou Zhu ◽  
Chun Xiao Cao ◽  
Ming Gao Yan
Keyword(s):  
Titanium Alloy ◽  
Rare Earth ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Strain Range ◽  
Cyclic Softening ◽  
Propagation Model ◽  
Cyclic Behavior ◽  
Transgranular Fracture ◽  
Creep Fatigue

Low cyclic behavior of a new type near-α titanium alloy containing rare earth Nd (Ti60) with and without dwell time introduced at maximum tensile strain has been investigated at ambient temperature and 600°C. The results show that, Ti60 alloy exhibits a cyclic softening behavior at almost all strain levels being investigated. The cyclic processes show good agreement with predictions based on the fatigue crack propagation model. At 600°C, the LCF life of Nd-bearing near-α titanium alloy is superior to that at room temperature within the investigated strain range, which indicates that Ti60 alloy is a good candidate for high temperature component under complicated load and temperature conditions. The results also show that the creep-fatigue interaction is related to the strain range applied. The creep-fatigue fracture is characterized by transgranular fracture mode due to the formation of matrix voids induced by Nd-bearing particles.

Fatigue Properties and Microstructure of SnAgCu Bi-Based Solder Joint

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Minghong Jian ◽  
Sinan Su ◽  
Sa'd Hamasha ◽  
Mohammad M. Hamasha ◽  
Atif Alkhazali
Keyword(s):  
Fatigue Life ◽  
Plastic Strain ◽  
Solder Joint ◽  
Solder Joints ◽  
Hysteresis Loops ◽  
Strain Range ◽  
Fatigue Performance ◽  
Fatigue Properties ◽  
Solder Alloys ◽  
Plastic Strain Range

Abstract The reliability of solder joints plays a critical role in electronic assemblies. SnAgCu solder alloys with doped elements such as Bi and Sb is one of the candidates for high reliability applications. However, the mechanical and fatigue properties of the actual solder joint structure have not been studied for these new alloys. In this paper, a cyclic fatigue test was conducted on individual real solder joints of different alloys, including SnAgCu, SnCu–Bi, SnAgCu–Bi, and SnAgCu–BiSb. The fatigue property of those solder joints was analyzed based on the characteristic fatigue life and stress–strain, hysteresis, loops. The results show that solder joints with both Ag and Bi content have a better fatigue resistance than the solder joints with Ag or Bi content only. The results of SnAgCu and SnCu–Bi solder alloys show similar fatigue performance. Also, the fatigue performance of SnAgCu–Bi is close to SnAgCu–BiSb in the accelerated test. But the SnAgCu–Bi alloy is estimated to have a longer characteristic life under low-stress amplitude cycling. The microstructure analysis shows a bismuth-rich phase formed around the Ag3Sn precipitates. Adding bismuth in the solder alloy can significantly improve the fatigue properties through solid solution hardenings. On another hand, the plastic strain range and work dissipation were measured from the hysteresis loops for all tests. The Morrow Energy and the Coffin–Manson models were developed from the fitted data to predict the fatigue life as a function of work dissipation and plastic strain range.

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