scholarly journals Microstructural Evolution along the NiCrMoV Steel Welded Joints Induced by Low-Cycle Fatigue Damage

Metals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 811
Author(s):  
Shuo Weng ◽  
Yuhui Huang ◽  
Mingliang Zhu ◽  
Fuzhen Xuan
Keyword(s):  
Dislocation Density ◽  
Grain Boundaries ◽  
Strain Amplitude ◽  
Microstructural Evolution ◽  
Welded Joints ◽  
Low Cycle Fatigue ◽  
Tensile Tests ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Nicrmov Steel

The degradation of mechanical properties of materials is essentially related to microstructural changes under service loadings, while the inhomogeneous degradation behaviors along welded joints are not well understood. In the present work, microstructural evolution under low-cycle fatigue in base metal (BM) and weld metal (WM) of NiCrMoV steel welded joints were investigated by miniature tensile tests and microstructural observations. Results showed that both the yield strength and ultimate tensile strength of the BM and WM decreased after low-cycle fatigue tests, which were attributed to the reduction of dislocation density and formation of low-energy structures. However, the microstructural evolution mechanisms in BM and WM under the same cyclic loadings were different, i.e., the decrease of dislocation density in BM was attributed to the dislocation pile-ups along the grain boundaries, dislocation tangles around the carbides at the lower strain amplitudes (±0.3% or ±0.5%). Additionally, when the strain amplitude was ±8%, the dislocation density was further decreased by the formation of subgrains in BM. For WM, the dislocation density decreased with the increase of strain amplitude, which was mainly caused by the dislocation pile-ups along the grain boundaries and the formation of subgrains.

Internal Crack Initiation in Low-Cycle Fatigue of Stainless Steel

2010 ◽  
Author(s):  
Masayuki Kamaya ◽  
Masahiro Kawakubo
Keyword(s):  
Stainless Steel ◽  
Crack Initiation ◽  
Strain Amplitude ◽  
Low Cycle Fatigue ◽  
Fatigue Tests ◽  
Internal Crack ◽  
Surface Cracks ◽  
Cycle Fatigue ◽  
Type Specimens ◽  
316 Stainless Steel

Internal cracks were observed on the fracture surface of Type 316 stainless steel specimens subjected to a low-cycle fatigue test, in which the strain amplitude was more than 1%. In some cases the specimens fractured due to these internal cracks. In this study, the reason and conditions for the internal crack initiation were examined. Fatigue experiments were conducted using Type 316 stainless steel. In order to enhance the internal crack initiation, the specimens were subjected to pre-damaging and surface cracks were removed before the start of the fatigue tests. It was shown that specimens fractured due to internal cracks when the strain amplitude of pre-damaging was more than 1% and hourglass-type specimens were used. The fatigue life was reduced largely due to the internal cracks and the magnitude of reduction was more significant for the smaller strain amplitude of the fatigue tests. Inclusions were observed at the origin of some internal cracks. It was deduced that the hourglass geometry of the specimen enhanced the internal crack initiation. Namely, the multi-axial field was one of the factors promoting the internal crack initiation.

Development of a Model for Low-Cycle Fatigue Assessment of 347 SS Butt-Welded Joints

2013 ◽  
Author(s):  
Eliane Lang ◽  
Jürgen Rudolph ◽  
Heinz Thomas Beier ◽  
Michael Vormwald
Keyword(s):  
Welded Joints ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Detailed Model ◽  
Butt Weld ◽  
New Approach ◽  
Fatigue Assessment ◽  
3D Scans

This contribution deals with the low cycle fatigue behavior of butt-welded joints of austenitic stainless steel (1.4550, type 347). The focus is on the problem how to model these welded joints adequately with the objective of its assessment. Thereby, the differences between as-welded and machined weld are considered, in addition. The considerations — presented here — are based on previous investigations reported by Lang et al. [10]. Therein, a new approach was proposed in order to determine the local strains and the LCF relevant influence of the butt weld. It is based on material mechanics and includes an accurate modeling of the real weld geometry — based on 3D scans with very high resolution. Originating from this detailed model an idealized model is derived that takes into account significant parameters of a butt weld. In addition, the inhomogeneity of the weld is considered in the model, now, that has previously been ignored. Therefore, the part around the weld was partitioned in material zones according to their hardness. The underlying hardness measurements revealed significant influences of the load history. The results of the numerical simulations based on the new model are compared to them of the scan-based model and the measuring results from related fatigue tests. Considering further fatigue influences as the size and surface roughness the new approach is intended to be adopted in a global design and calculation concept for low-cycle fatigue assessment of butt-welded joints — applicable for normal users.

scholarly journals An Energy-Based Unified Approach to Predict the Low-Cycle Fatigue Life of Type 316L Stainless Steel under Various Temperatures and Strain-Rates

Materials ◽  
2019 ◽  
Vol 12 (7) ◽  
pp. 1090 ◽  
Author(s):  
Nae Tak ◽  
Jung-Seok Kim ◽  
Jae-Yong Lim
Keyword(s):  
Stainless Steel ◽  
Strain Rate ◽  
316L Stainless Steel ◽  
Low Cycle Fatigue ◽  
Tensile Tests ◽  
Fatigue Tests ◽  
Strain Rates ◽  
Cycle Fatigue ◽  
Type 316L ◽  
Type 316L Stainless Steel

An energy-based low-cycle fatigue model was proposed for applications at a range of temperatures. An existing model was extended to the integrated approach, incorporating the simultaneous effects of strain rate and temperature. A favored material at high temperature, type 316L stainless steel, was selected in this study and its material characteristics were investigated. Tensile tests and low-cycle fatigue tests were performed using several strain rates at a temperature ranging from room temperature to 650 °C. Material properties were obtained in terms of temperature using the displacement-controlled tensile tests and further material response were investigated using strain-controlled tensile tests. Consequently, no pronounced reduction in strengths occurred at temperatures between 300 and 550 °C, and a negative strain rate response was observed in the temperature range. Based on the low-cycle fatigue tests by varying strain rates and temperature, it was found that a normalized plastic strain energy density and a strain-rate modified cycle were successfully correlated. The accuracy of the model was discussed by comparing between predicted and experimental lives.

Crack Formation in Membrane Electrode Assembly Under Static and Cyclic Loadings

2013 ◽  
Vol 10 (2) ◽  
Author(s):  
Yusuke Kai ◽  
Yuki Kitayama ◽  
Masaki Omiya ◽  
Tomoaki Uchiyama ◽  
Manabu Kato
Keyword(s):  
Crack Formation ◽  
Low Cycle Fatigue ◽  
Test Chamber ◽  
Tensile Tests ◽  
Fatigue Tests ◽  
Proton Exchange ◽  
Operating Conditions ◽  
Membrane Electrode ◽  
Cycle Fatigue ◽  
Ambient Conditions

The mechanical reliability of membrane electrode assemblies (MEAs) in polymer electrolyte fuel cells (PEFCs) is a major concern for fuel cell vehicles. Hygrothermal cyclic conditions induce mechanical stress in MEAs and cracks form under operating conditions. This paper investigates the failure mechanism of MEAs under several mechanical and environmental conditions with the aim of designing durable PEFCs. We performed static tensile tests and low-cycle fatigue tests on MEAs. During the tensile tests, the temperature and humidity of the test chamber were controlled and surface crack formation of MEAs was observed in situ by a video microscope. Low-cycle fatigue tests were performed at ambient conditions and the number of cycles to crack formation was measured. The results reveal that the temperature and the humidity affect the mechanical properties of MEA. Observations of MEAs during tensile tests reveal that cracks form on the surface of catalyst layers immediately after the MEAs yield. These results indicate that reducing the deformation mismatch between the catalyst layer and the proton exchange membrane is important for suppressing crack formation in MEAs. The results of low-cycle fatigue tests reveal that the fatigue strength of a MEA follows the Coffin–Manson law so that fatigue design of MEAs based on the Coffin–Manson law is possible. This result is valuable for designing durable PEFCs.

Cyclic Stress-Strain Behavior and Low-Cycle Fatigue of Ti 6-4 at 260°C

1992 ◽  
Vol 114 (4) ◽  
pp. 390-398 ◽  
Author(s):  
T. Bui-Quoc ◽  
R. Gomuc ◽  
A. Biron
Keyword(s):  
Strain Amplitude ◽  
Low Cycle Fatigue ◽  
Strain Curve ◽  
Cyclic Stress ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Stress Strain ◽  
Strain Behavior ◽  
Show Evidence ◽  
Strain Cycling

Low-cycle fatigue tests on Ti 6-4 (Ti-6Al-4V) have been carried out at 260°C under strain-controlled conditions with constant strain amplitude and increasing multistep strain levels. The results of constant strain amplitude tests were used to establish the fatigue diagram whereas the multistep tests were examined to assess the cyclic stress-strain behavior in comparison with the conventional stress-strain curve. Most of the tests were carried out under zero-to-tension conditions in the intermediatecycle range (Nf ≃ 3 x 103 to 105 cycles). The effect of prior strain cycling on the tensile properties was also investigated. The experimental data is discussed together with theoretical evaluations. In addition, microstructural examinations of the rupture surfaces have been made to show evidence on the type of crack initiation sites and on the crack propagation modes at different strain levels.

Crack Formation on Membrane Electrode Assembly (MEA) Under Static and Cyclic Loadings

2012 ◽  
Author(s):  
Yusuke Kai ◽  
Yuki Kitayama ◽  
Masaki Omiya ◽  
Tomoaki Uchiyama ◽  
Manabu Kato
Keyword(s):  
Crack Formation ◽  
Low Cycle Fatigue ◽  
Tensile Tests ◽  
Fatigue Tests ◽  
Proton Exchange ◽  
Operating Conditions ◽  
Membrane Electrode ◽  
Cycle Fatigue ◽  
Critical Design ◽  
Temperature And Humidity

Mechanical reliabilities of membrane electrode assemblies (MEA) in polymer electrolyte fuel cells (PEFCs) are a major concern to fuel cell vehicles. Hygro-thermal cyclic conditions induce the mechanical stress in MEA and cracks are formed under operating conditions. The purpose of this paper is to understand the failure mechanism of MEA under several mechanical and environmental conditions for the critical design of durable PEFCs. We carried out both static tensile tests and low cycle fatigue tests for MEA. For tensile tests, temperature and humidity in a test chamber were controlled and the surface crack formation of MEA was observed by a video micro scope in situ. Low cycle fatigue tests were carried out in room condition and the number of cycles to crack formation was measured. The results showed that the mechanical properties of MEA were influenced by temperature and humidity. The observations of MEA during tensile tests revealed that cracks were formed on the surface of catalyst layers just after the yielding of MEA. This result indicates that the deformation mismatch between catalyst layer and proton exchange membrane (PEM) is an important parameter to suppress the crack formation in MEA. The results of low cycle fatigue tests revealed that the fatigue strength of MEA followed the Coffin-Manson law and the fatigue design of MEA based on the Coffin-Manson law is possible. This result is valuable for the critical design of durable PEFCs.

Experimental investigation on low cycle fatigue properties of Ni-based alloy with single hole

2020 ◽  
Vol 111 (6) ◽  
pp. 519-525
Author(s):  
Zhenwei Li ◽  
Hangshan Gao ◽  
Zhaohan Wang ◽  
Yanchao Zhao ◽  
Zhixun Wen ◽  
...  
Keyword(s):  
Microstructural Evolution ◽  
Stress Level ◽  
Film Cooling ◽  
Low Cycle Fatigue ◽  
Fatigue Tests ◽  
Fatigue Properties ◽  
Cycle Fatigue ◽  
Cooling Hole ◽  
Surface Morphologies ◽  
Fracture Morphologies

Abstract The low-cycle fatigue properties of the Ni-based superalloy K416B with single film cooling hole were investigated. The low-cycle fatigue tests were carried out using tension cycling under stress-controlled conditions (stress ratio R = 0.1) at room temperature. The fatigue limit lives of the perforated samples were determined by the lifting method. The fracture morphologies and microstructural evolution were examined. The results showed that the fatigue crack initiated from the film cooling hole. Furthermore, fracture paths and surface morphologies of the samples were influenced significantly by the stress level. The analysis of the microstructural evolution further indicated that the fatigue failure mechanisms of the samples with a film cooling hole depended on the stress level.

scholarly journals Low- and High-Cycle Fatigue Behavior of FRCM Composites

Materials ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5412
Author(s):  
Angelo Savio Calabrese ◽  
Tommaso D’Antino ◽  
Pierluigi Colombi ◽  
Carlo Poggi
Keyword(s):  
Cyclic Loading ◽  
High Cycle Fatigue ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Strain Curve ◽  
Tensile Tests ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Stress Strain ◽  
Static Tensile

This paper describes methods, procedures, and results of cyclic loading tensile tests of a PBO FRCM composite. The main objective of the research is the evaluation of the effect of low- and high-cycle fatigue on the composite tensile properties, namely the tensile strength, ultimate tensile strain, and slope of the stress–strain curve. To this end, low- and high-cycle fatigue tests and post-fatigue tests were performed to study the composite behavior when subjected to cyclic loading and after being subjected to a different number of cycles. The results showed that the mean stress and amplitude of fatigue cycles affect the specimen behavior and mode of failure. In high-cycle fatigue tests, failure occurred due to progressive fiber filaments rupture. In low-cycle fatigue, the stress–strain response and failure mode were similar to those observed in quasi-static tensile tests. The results obtained provide important information on the fatigue behavior of PBO FRCM coupons, showing the need for further studies to better understand the behavior of existing concrete and masonry members strengthened with FRCM composites and subjected to cyclic loading.

Sign in / Sign up

Export Citation Format

Share Document