Continuous Creep Damage Monitoring Using a Novel Potential Drop Technique

2011 ◽  
Author(s):  
Catrin M. Davies ◽  
Peter Nagy ◽  
Aditya Narayanan ◽  
Peter Cawley
Keyword(s):  
Creep Strain ◽  
Low Frequency ◽  
Creep Damage ◽  
Potential Drop ◽  
In Situ Monitoring ◽  
Creep Tests ◽  
Damage Monitoring ◽  
Accelerated Creep ◽  
Resistivity Variation

A new directional low-frequency Alternating Current Potential Drop (ACPD) technique has been developed for continuous in-situ monitoring of creep strain and damage in alloys. The sensor relies on a modified ACPD technique that measures simultaneously both values of resistance in the axial and lateral directions using a square electrode configuration. The technique monitors the variation in the ratio of the measured axial and lateral resistances, therefore can efficiently separate the mostly isotropic common part of the resistivity variation caused by reversible temperature variations from the mostly anisotropic differential part caused by direct geometrical and indirect material effects of creep. Initially, this ratio can be considered proportional to the axial creep strain, while at later stages, the resistance ratio accelerates due to the formation of directional discontinuities such as preferentially oriented grain boundary cavities and micro-cracking in the material. This ACPD technique has been applied to a series of accelerated creep tests on 2.25CrMoV Steel at 650 °C. The results are presented and the application of the method for online component monitoring is discussed.

scholarly journals Experimental and Theoretical Studies on the Creep Behavior of Bayer Red Mud

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Baoyun Zhao ◽  
Wei Huang ◽  
Zhile Shu ◽  
Mengmeng Han ◽  
Yanbo Feng
Keyword(s):  
Creep Strain ◽  
Creep Behavior ◽  
Red Mud ◽  
Damage Model ◽  
Creep Damage ◽  
Creep Model ◽  
Creep Tests ◽  
Accelerated Creep ◽  
Bayer Red Mud ◽  
Creep Damage Model

Long-term stability and safety of the Bayer red mud (BRM) disposal field is very important for the local residents’ life, which necessitates the knowledge of its creep behavior. In order to investigate the creep behavior of BRM, a series of triaxial drained creep tests were conducted by using an improved triaxial creep apparatus. The results indicate that the creep behavior of BRM is significant with confining and deviatoric stresses being critical factors. The creep strain is in a nonlinear relationship with stress and time, and a larger deviator stress will lead to a larger creep strain. The main failure mechanism of BRM is plastic shear, accompanied by a significant compression and ductile dilatancy. Based on the test results, two well-established creep models, the Burgers creep model and Singh–Mitchell creep model, were used to comparatively analyze the creep behavior of the Bayer red mud under a certain stress level. Then, an improved Burgers creep damage constitutive model with the addition of a damage variable was proposed, whose parameters were also analyzed in detail. The comparison of the calculated values of the creep model and the experimental values shows that the proposed creep damage model can better describe the instant elastic deformation, attenuation creep, steady-state creep, and accelerated creep stages of the Bayer red mud.

In-Process Damage Monitoring and Stress Analysis of Thermal Spray Coating

2007 ◽  
Vol 353-358 ◽  
pp. 2403-2406
Author(s):  
Koichi Taniguchi ◽  
Manabu Enoki ◽  
Koichi Tomita
Keyword(s):  
Thermal Spray ◽  
Laser Interferometer ◽  
Spray Coating ◽  
Thermal Spray Coating ◽  
In Situ Monitoring ◽  
Spray Coatings ◽  
Damage Monitoring ◽  
Process Damage ◽  
Ae Signals

AE method is a well-known technique for in-situ monitoring of damage behavior by attached piezoelectric transducer. However, this conventional detection of AE signals has certain limitations. In recent years, numerous efforts have addressed the substitution of laser-based techniques for ultrasonic nondestructive evaluation in place of conventional piezoelectric transducers. Especially, a laser interferometer can be used to measure a displacement or velocity at materials surface using Doppler-shift. However, there are few reports referring to the detection of AE signals in the practical materials and testing because of the difficulty of experiments. We developed the AE measurement system with laser interferometer to apply this technique to microcrack evaluation and reported the quantitative AE analysis in various materials. This paper demonstrates AE results from thermal spray coatings at elevated temperature.

The Need for In-Situ Pipe Support Testing

2004 ◽  
Author(s):  
Gerry May
Keyword(s):  
Creep Damage ◽  
Cost Effective ◽  
Piping System ◽  
Design Load ◽  
Cost Effective Method ◽  
Accelerated Creep ◽  
Constant Support ◽  
Full Operation

Pipe support functionality is critical to the long term life of piping system. Spring supports degrade with time due to flexing in the spring and wear in constant support bearings. It is not unusual to measure constant support hangers with resistance 25% to 50% different than the design load. This leads to excessive sustained pipe stress, pipe sag (or uplift), and in high temperature systems, accelerated creep damage. Supports may also not move properly from shut down to full operation, which can create excessive fatigue stress, failed hanger components, and other piping system damage. In-situ hanger testing has been found to be a reliable and cost effective method to determine the functionality of pipe supports. Results are used as input to set revised recommended loads, and to determine if any hangers need to be replaced. This paper provides examples of the types of problems that are often found in the field, the method to test, and typical resolutions to maximize the pipe life and minimize the risk of failure.

scholarly journals In Situ 3D-µ-Tomography on Particle-Reinforced Light Metal Matrix Composite Materials under Creep Conditions

Metals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 1034
Author(s):  
Bettina Camin ◽  
Lennart Hansen
Keyword(s):  
Metal Matrix Composites ◽  
Creep Strain ◽  
Metal Matrix ◽  
Creep Damage ◽  
Light Metal ◽  
Ex Situ ◽  
Sufficient Information ◽  
Matrix Composites ◽  
Damage Mechanisms

In transportation light metal matrix composites (L-MMCs) are used increasingly due to their improved creep resistance even at higher application temperatures. Therefore, the creep behavior and failure mechanisms of creep loaded particle reinforced L-MMCs have been investigated intensively. Until now, creep damage analyses are usually performed ex situ by means of interrupted creep experiments. However, ex situ methods do not provide sufficient information about the evolution of creep damage. Hence, in situ synchrotron X-ray 3D-µ-tomography investigations were carried out enabling time and space resolved studies of the damage mechanisms in particle-reinforced titanium- and aluminum-based metal matrix composites (MMCs) during creep. The 3D-data were visualized and existing models were applied, specifying the phenomenology of the damage in the early and late creep stages. During the early stages of creep, the damage is determined by surface diffusion in the matrix or reinforcement fracture, both evolving proportionally to the macroscopic creep curve. In the late creep stages the damage mechanisms are quite different: In the Al-MMC, the identified mechanisms persist proportional to creep strain. In contrast, in the titanium-MMC, a changeover to the mechanism of dislocation creep evolving super-proportionally to creep strain occurs.

Numerical Back Inversion Method of Compressive Creep Parameters of Rock Masses under Rigid Bearing Plate and its Application

2008 ◽  
Vol 33-37 ◽  
pp. 429-434 ◽  
Author(s):  
Wen Dong Yang ◽  
Qiang Yong Zhang ◽  
Jian Guo Zhang
Keyword(s):  
Back Analysis ◽  
In Situ Monitoring ◽  
Inversion Method ◽  
Rock Masses ◽  
Creep Tests ◽  
Compressive Creep ◽  
Bearing Plate ◽  
In Situ Conditions ◽  
Dam Site

Due to lots of hypothesis, the theoretical analytical solution of the creep parameters inversion can not reflect the in-situ conditions actually. In order to simulate the process of the compressive creep tests of the in-situ bearing plate, the affection of the stratum distribution and the influence of the geological status in site actually, FLAC3D is used and numerical back analysis method of the creep parameters at dam site is set up. Based on the in-situ compressive creep tests’ data of the diabase rock masses at Dagangshan dam site, creep parameters are got with this method. Results indicate that the numerical calculated displacements of the compressive creep are similar to the in-situ monitoring displacements. It reveals that with this numerical method creep parameters can be backing analyzed logically. This supplies technical assurances to stability estimate and analysis of rock masses in slope projects.

scholarly journals Analysis of Fatigue Life of PMMA at Different Frequencies Based on a New Damage Mechanics Model

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Aifeng Huang ◽  
Weixing Yao ◽  
Fang Chen
Keyword(s):  
Fatigue Life ◽  
Damage Mechanics ◽  
Low Cycle Fatigue ◽  
Low Frequency ◽  
Creep Damage ◽  
Cyclic Creep ◽  
Continuum Damage Mechanics ◽  
Creep Tests ◽  
Damage Evolution Equation ◽  
Load Rate

Low-cycle fatigue tests at different frequencies and creep tests under different stress levels of Plexiglas Resist 45 were conducted. Correspondingly, the creep fracture time,S-Ncurves, cyclic creep, and hysteresis loop were obtained. These results showed that the fatigue life increases with frequency at low frequency domain. After analysis, it was found that fatigue life is dependent on the load rate and is affected by the creep damage. In addition, a new continuum damage mechanics (CDM) model was established to analyze creep-fatigue life, where the damage increment nonlinear summation rule was proposed and the frequency modification was made on the fatigue damage evolution equation. Differential evolution (DE) algorithm was employed to determine the parameters within the model. The proposed model described fatigue life under different frequencies, and the calculated results agreed well with the experimental results.

scholarly journals Calibration of CDM-Based Creep Constitutive Model Using Accelerated Creep Test (ACT) Data

2020 ◽  
Author(s):  
Md Abir Hossain ◽  
Robert Mach ◽  
Jacob Pellicotte ◽  
Calvin M. Stewart
Keyword(s):  
Constitutive Model ◽  
Creep Strain ◽  
Creep Deformation ◽  
Numerical Optimization ◽  
Creep Damage ◽  
Deformation Curve ◽  
Long Duration ◽  
Processing Procedure ◽  
Accelerated Creep ◽  
Damage Constitutive Model

Abstract In conventional creep testing (CCT) a specimen is subject to constant load and temperature for a long-duration until creep rupture occurs. Conventional testing can be costly when considering the number of experiments needed to characterize the creep response of a material over a range of stress and temperature. To predict long-term creep-rupture properties, the time-temperature-stress superposition principle (TTSSP) approach has been employed where stress and/or temperature is applied at an elevated level; the result of which are extrapolated down to low stress and/or temperature conditions. These methods have been successful in predicting minimum-creep-strain-rate (MCSR) and stress-rupture (SR) but suffer from an inability to predict the creep deformation curve or account for changes in deformation mechanisms or aging that occurs at long-duration. An accelerated technique, termed the Stepped isostress method (SSM) allows the accelerated testing of materials to determine their creep deformation response. Unlike TTSSP tests, the SSM test employs a single specimen where the stress is periodically step increased until rupture. The SSM creep deformation curve is processed (time and strain shifted) to produce an accelerated creep deformation curve that represent the creep deformation curve at the initial stress level in SSM. A processing procedure for metals has yet to be developed. The research objective of this study is to develop a processing procedure for SSM test data using a creep-damage constitutive model. Triplicate SSM tests were conducted on Ni-based superalloy Inconel 718 at 650°C with stress being periodically increased until rupture. Triplicate CCT tests were conducted at the initial stress level of the SSM tests. The Sine-hyperbolic (Sinh) creep-damage model was employed in this study. The Sinh creep-damage constitutive model is based on coupled creep strain rate and damage evolution equations; where both rates are dependent on the current state of damage. Calibration is two-step: analytical and numerical optimization. Each stepped creep deformation curve is tackled quasi-analytically to determine MCSR and SR related material constants and accumulated damage. The damage accumulated at the end of each step was then passed onto subsequent steps to calibrate the MCSR, rupture prediction, and damage evolution. Numerical optimization was applied to optimize model constants involved in the creep strain constitutive equations in order to generate best-fitted Sinh creep deformation curves. The Sinh model predictions were compared to the SSM and CCT data. The Sinh model satisfactorily predicts the SSM data and thus the calibrated material constants provides a good estimate of rupture found in the CCT data. Calibration using SSM data reduces the number of tests needed to calibrate a model; significantly reducing costs. A single SSM test replaces numerous creep tests at different stresses.

In situ monitoring of cocrystals in formulation development using low-frequency Raman spectroscopy

2018 ◽  
Vol 542 (1-2) ◽  
pp. 56-65 ◽  
Author(s):  
Takashi Otaki ◽  
Yuta Tanabe ◽  
Takashi Kojima ◽  
Masaru Miura ◽  
Yukihiro Ikeda ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Low Frequency ◽  
In Situ Monitoring ◽  
Formulation Development
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