scholarly journals Experimental Investigation and Modeling of Damage Accumulation of EN-AW 2024 Aluminum Alloy under Creep Condition at Elevated Temperature

Materials ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 404
Author(s):  
Adam Tomczyk ◽  
Andrzej Seweryn
Keyword(s):  
Damage Accumulation ◽  
Axial Stress ◽  
Axial Strain ◽  
Creep Condition ◽  
Creep Damage ◽  
Creep Rupture ◽  
Uniaxial Tensile ◽  
Creep Tests ◽  
Damage State ◽  
2024 Aluminum Alloy

The paper is focused on creep-rupture tests of samples made of the 2024 alloy in the T3511 temper under uniaxial tensile stress conditions. The basic characteristics of the material at the temperatures of 100, 200 and 300 °C were determined, such as the Young’s modulus E, yield point σy, ultimate tensile strength σc and parameters K and n of the Ramberg–Osgood equation. Creep tests were performed for several different levels of nominal axial stress (load) at each temperature. It was observed that in the process of creep to failure at 200 and 300 °C, as the stress decreases, the creep time increases and, at the same time, the strain at rupture increases. However, such a regularity is maintained until a certain transition stress value σt is reached. Reducing the stress below this value results in a decreased value of the strain at rupture. A simple model of creep damage accumulation was proposed for the stress range above the transient value. In this model, the increase in the isotropic damage state variable was made dependent on the value of axial stress and the increase in plastic axial strain. Using the results of experimental creep-rupture tests and the failure condition, the parameters of the proposed model were determined. The surface of fractures obtained in the creep tests with the use of SEM technology was also analyzed.

Development of continuum damage in the creep rupture of notched bars

1984 ◽  
Vol 311 (1516) ◽  
pp. 103-129 ◽  
Keyword(s):  
New York ◽  
Damage Mechanics ◽  
Axial Stress ◽  
Numerical Procedure ◽  
Creep Damage ◽  
Continuum Damage Mechanics ◽  
Constant Load ◽  
Creep Rupture ◽  
Continuum Damage ◽  
Discrete Crack

The creep rupture of circumferentially notched, circular tension bars which are subjected to constant load for long periods at constant temperature is studied both experimentally and by using a time-iterative numerical procedure which describes the formation and growth of creep damage as a field quantity. The procedure models the development of failed or cracked regions of material due to the growth and linkage of grain boundary defects. Close agreement is shown between experimental and theoretical values of the representative rupture stress, of the zones of creep damage and of the development of cracks for circular (Bridgman, Studies in large plastic flow and fracture , New York: McGraw-Hill (1952)) and British Standard notched specimens (B.S. no. 3500 (1969)). The minimum section of the circular notch is shown to be subjected to relatively uniform states of multi-axial stress and damage while the B.S. notch is shown to be subjected to non-uniform stress and damage fields in which single cracks grow through relatively undamaged material. The latter situation is shown to be analogous to the growth of a discrete crack in a lightly damaged continuum. The continuum damage mechanics theory presented here is shown to be capable of accurately predicting these extreme types of behaviour.

scholarly journals Estimating the Influences of Prior Residual Stress on the Creep Rupture Mechanism for P92 Steel

Metals ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 639 ◽  
Author(s):  
Dezheng Liu ◽  
Yan Li ◽  
Xiangdong Xie ◽  
Guijie Liang ◽  
Jing Zhao
Keyword(s):  
Residual Stress ◽  
Flow Stress ◽  
Power Plants ◽  
Creep Damage ◽  
Creep Rupture ◽  
Transgranular Fracture ◽  
Creep Tests ◽  
Energy Principle ◽  
P92 Steel ◽  
Rupture Mechanism

Creep damage is one of the main failure mechanisms of high Cr heat-resistant steel in power plants. Due to the complex changes of stress, strain, and damage at the tip of a creep crack with time, it is difficult to accurately evaluate the effects of residual stress on the creep rupture mechanism. In this study, two levels of residual stress were introduced in P92 high Cr alloy specimens using the local out-of-plane compression approach. The specimens were then subjected to thermal exposure at the temperature of 650 °C for accelerated creep tests. The chemical composition of P92 specimens was obtained using an FLS980-stm Edinburgh fluorescence spectrometer. Then, the constitutive coupling relation between the temperature and material intrinsic flow stress was established based on the Gibbs free energy principle. The effects of prior residual stress on the creep rupture mechanism were investigated by the finite element method (FEM) and experimental method. A comparison of the experimental and simulated results demonstrates that the effect of prior residual stress on the propagation of micro-cracks and the creep rupture time is significant. In sum, the transgranular fracture and the intergranular fracture can be observed in micrographs when the value of prior residual stress exceeds and is less than the material intrinsic flow stress, respectively.

Evaluation of Microstructures and Creep Damages in the HAZ of P91 Steel Weldment

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
Masaaki Tabuchi ◽  
Hiromichi Hongo ◽  
Yongkui Li ◽  
Takashi Watanabe ◽  
Yukio Takahashi
Keyword(s):  
Welded Joints ◽  
Damage Mechanics ◽  
Early Stage ◽  
Axial Stress ◽  
Creep Damage ◽  
Specimen Thickness ◽  
Creep Tests ◽  
Fine Grained ◽  
Type Iv

The creep strength of welded joints in high Cr steels decreases due to the formation of Type IV creep damage in heat-affected zones (HAZs) during long-term use at high temperatures. This paper aims to elucidate the processes and mechanisms of Type IV creep damage using Mod.9Cr–1Mo (ASME Grade 91) steel weldments. Long-term creep tests for base metal, simulated fine-grained HAZ, and welded joints were conducted at 550°C, 600°C, and 650°C. Furthermore, creep tests of thick welded joint specimens were interrupted at 0.1, 0.2, 0.5, 0.7, 0.8, and 0.9 of rupture life and damage distributions were measured quantitatively. It was found that creep voids were initiated at an early stage of life inside the specimen thickness and coalesced to form cracks at a later stage of life. Creep damage was observed mostly at 25% below the surface of the plate. Experimental creep damage distributions were compared with computed versions using finite element method and damage mechanics analysis. Both multi-axial stress state and strain concentration in fine-grained HAZ appear to influence the formation and distribution of creep voids.

Enhanced Creep Life Evaluations for Grade 91 Circumferential Weldments

2017 ◽  
Author(s):  
Marvin J. Cohn
Keyword(s):  
Applied Stress ◽  
Hoop Stress ◽  
Axial Stress ◽  
Creep Damage ◽  
Creep Rupture ◽  
Piping System ◽  
Remaining Life ◽  
Creep Life ◽  
Rupture Properties ◽  
Applied Stresses

The basic power piping creep life calculations consider the important variables of time, temperature and stress for the creep rupture properties of the unique material. Some engineering evaluations of remaining life estimate the applied stress as the design stress obtained from a conventional piping stress analysis. Other remaining life evaluations may assume that a conservative estimate of the applied stress is no greater than the hoop stress due to pressure. The creep rupture properties of the unique material are usually obtained from the base material creep rupture properties. The typical methodologies to estimate remaining life do not consider the actual applied stress due to malfunctioning supports, multiaxial stress effects, axial and through-wall creep redistribution, time-dependent material-specific weldment creep rupture properties, residual welding stresses, and actual operating temperatures and pressures. It has been determined that the initiation and propagation of Grade 91 creep damage is a function of stress to about the power of 9 at higher applied stresses. There have been many examples of malfunctioning piping supports creating unintended high stresses. When the axial stress is nearly as high as the hoop stress, the applicable corresponding uniaxial stress for creep rupture life is increased about 30%. Multiaxial stress effects in circumferential weldments (e.g., when the axial stress is nearly as high as the hoop stress) can reduce the weldment creep life to less than 1/6th of the predicted life assuming a uniaxial stress or hoop stress due to pressure only. Since 2012, the ASME B31.1 Code has required that significant piping displacement variations from the expected design displacements shall be considered to assess the piping system’s integrity [1]. This paper discusses a strategy for an enhanced creep life evaluation of power piping circumferential weldments. Piping stresses can vary by a factor greater than 2.0. Consequently, the range of circumferential weldment creep rupture lives for a single piping system may vary by a factor as high as 40. Although there is uncertainty in the operating times at temperatures and pressures, all of the weldments within the piping system have the same time, temperatures, and pressures, so the corresponding uncertainties for these three attributes are normalized within the same piping system. Since the applied stresses are the most important weld-to-weld variable within a piping system, it is necessary to have an accurate evaluation of the applied stresses to properly rank the creep rupture lives of the circumferential weldments. This methodology has been successfully used to select the lead-the-fleet creep damage in circumferential weldments over the past 15 years.

scholarly journals High-Temperature Tensile and Creep Behavior in a CrMoV Steel and Weld Metal

Materials ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 109
Author(s):  
Yan Song ◽  
Mengyu Chai ◽  
Zelin Han ◽  
Pan Liu
Keyword(s):  
High Temperature ◽  
Weld Metal ◽  
Creep Damage ◽  
Uniaxial Tensile ◽  
Second Phase ◽  
Creep Tests ◽  
Damage Mechanisms ◽  
Integrity Assessment ◽  
Steel Weldment ◽  
High Temperature Tensile

The 2.25Cr1Mo0.25V steel is a vanadium-modified 2.25Cr1Mo steel and is being widely used in the manufacture of heavy-wall hydrogenation reactors in petrochemical plants. However, the harsh service environment requires a thorough understanding of high-temperature tensile and creep behaviors of 2.25Cr1Mo0.25V steel and its weld for ensuring the safety and reliability of hydrogenation reactors. In this work, the high-temperature tensile and creep behaviors of base metal (BM) and weld metal (WM) in a 2.25Cr1Mo0.25V steel weldment used for a hydrogenation reactor were studied experimentally, paying special attention to its service temperature range of 350–500 °C. The uniaxial tensile tests under different temperatures show that the WM has higher strength and lower ductility than those of BM, due to the finer grain size in the WM. At the same time, the short-term creep tests at 550 °C reveal that the WM has a higher creep resistance than that of BM. Moreover, the creep damage mechanisms were clarified by observing the fracture surface and microstructures of crept specimens with the aid of scanning electron microscopy (SEM). The results showed that the creep damage mechanisms of both BM and WM are the initiation and growth of creep cavities at the second phase particles. Results from this work indicate that the mismatch in the high-temperature tensile strength, ductility, and creep deformation rate in 2.25Cr1Mo0.25V steel weldment needs to be considered for the design and integrity assessment of hydrogenation reactors.

A Study of Creep Damage Rules

1972 ◽  
Vol 94 (3) ◽  
pp. 533-541 ◽  
Author(s):  
M. M. Abo El Ata ◽  
I. Finnie
Keyword(s):  
Damage Accumulation ◽  
Creep Damage ◽  
Creep Rupture ◽  
Experimental Results ◽  
Initiation And Propagation ◽  
New Criterion ◽  
Present Understanding

A brief review is given of the literature on damage accumulation during creep and inadequacies in our present understanding are pointed out. By drawing on recent studies of the processes involved in creep-rupture, it is suggested that a new criterion for creep-damage accumulation may be proposed, which is more general than existing approaches. This involves the consideration of both the initiation and propagation phases of fracture, and it is seen that in some cases, strengthening rather than weakening may result from prior loadings. Experimental results are cited in support of these observations.

Identification of Stress Multiaxiallity Effect on Creep Damage by a Combination of Experiments and Numerical Analyses

2009 ◽  
Author(s):  
Yukio Takahashi
Keyword(s):  
Finite Element ◽  
Synergetic Effect ◽  
Stress Triaxiality ◽  
Creep Damage ◽  
Compact Tension ◽  
Simple Expression ◽  
Creep Rupture ◽  
Creep Tests ◽  
Element Analysis ◽  
Rupture Behavior

Structural materials experience various stress states and their integrity under a wide variety of stress multiaxility needs to be evaluated in design and life management for various components. Especially creep rupture behavior is known to be quite sensitive to the stress multiaxiality. To systematically evaluate the multiaxial effect on creep rupture behavior of modified 9Cr-1Mo steel, a number of creep tests were conducted on round-bar specimens with circumferential notches. Strong effects of temperature and deformation rate on the reduction of area were observed and their synergetic effect was modeled by a simple expression. Then crack growth in compact tension specimens was simulated by finite element analysis to derive ductility under higher stress triaxiality. Finally, true rupture strain was expressed as a function of temperature, inelastic strain rate and triaxiality factor and its validity was demonstrated through finite element analyses on notched bar and compact tension specimens employing it as a local fracture criterion.

Study on Creep Behaviors of T92 Steel under Multiaxial Stress State

2013 ◽  
Vol 860-863 ◽  
pp. 774-779
Author(s):  
Xue Ping Mao ◽  
Yang Yu ◽  
Chao Li ◽  
Sai Dong Huang ◽  
Hong Xu ◽  
...  
Keyword(s):  
Stress State ◽  
Rupture Life ◽  
Creep Damage ◽  
Creep Rupture ◽  
Failure Behavior ◽  
Multiaxial Stress ◽  
Creep Tests ◽  
Creep Ductility ◽  
Notched Specimen ◽  
Multiaxial Stress State

Creep tests for smooth specimens and notched specimens of T92 steel were carried out to study the effect of multiaxial stress state on creep rupture behaviors at 650°C. Creep rupture life was estimated by representative stress at multiaxial state of stress, the failure behavior of multiaxial creep was analyzed, and Kachanov creep damage formula was used to analyze the experimental data. The results show that the notch strengthens rupture life, multiaxial rupture behavior is controlled by mixed parameters, the creep ductility of the smooth and notched specimen decreases with rupture time, and damage factors of the smooth specimen and notched specimen are similar according to Kachanov formula.

Creep Damage Evaluation for Fine Grained HAZ of Mod. 9Cr Steels Under Multi-Axial Stress Conditions

2013 ◽  
Author(s):  
Kimiaki Yoshida ◽  
Masataka Yatomi ◽  
Masaaki Tabuchi ◽  
Ken-ichi Kobayashi
Keyword(s):  
Axial Stress ◽  
Stress Triaxiality ◽  
Creep Damage ◽  
Creep Rupture ◽  
Stress Conditions ◽  
Damage Evaluation ◽  
Metallographic Examination ◽  
Fine Grained ◽  
Notched Specimens ◽  
Triaxiality Factor

This study is concerned with the creep damage evaluation for the fine grained heat affected zone (HAZ) of modified 9Cr steels under multi-axial stress conditions. Circumferentially notched bar creep rupture and interrupted tests have been conducted on the simulated HAZ specimens of modified 9Cr Steels. A metallographic examination has been carried out to quantify creep damage accumulation in the specimens. It has been found from void observation that growth of creep void correlates with maximum principle stress and stress triaxiality factor. Finite element predictions based on ductility exhaustion approach have also been performed to predict the creep rupture time and creep damage in notched specimens. It has been concluded that a ductility exhaustion approach with empirical model provides reasonable life predictability almost in a scatter band of a factor of 2.

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