Fatigue Design Model Based on Damage Mechanisms Revealed by Acoustic Emission Measurements

1995 ◽  
Vol 117 (2) ◽  
pp. 200-208 ◽  
Author(s):  
D. Fang ◽  
A. Berkovits
Keyword(s):  
Acoustic Emission ◽  
Stress Ratio ◽  
Crack Nucleation ◽  
Load Cycle ◽  
Fatigue Tests ◽  
Damage Prediction ◽  
Fatigue Design ◽  
Final Failure ◽  
On Line ◽  
Selection Of

Integration of the microcomputer into acoustic emission instrumentation has brought AE monitoring of fatigue tests into the realm of practicality. On-line processing makes available a selection of software tools, enhancing classical techniques for eliminating the background noise which usually blanked out the desired data. Fatigue tests monitored for acoustic emission were carried out at room temperature on Incoloy 901 material specimens, over a stress-ratio range of −1 ≤ R ≤ .2. Valid AE data were obtained even when the load cycle passed through zero. The AE data permitted specific identification of the various phenomena occurring on the way to final failure. These included initial plasticity, crack nucleation and propagation phases. The AE findings were supported by microscopic examination. Based on the experimental data, a preliminary damage-prediction model was formulated.

Effects of chromic acid anodizing on fatigue behavior of 7050 T7451 aluminum alloy

2021 ◽  
Vol 63 (9) ◽  
pp. 805-810
Author(s):  
Çağrı İlhan ◽  
Rıza Gürbüz
Keyword(s):  
Aluminum Alloy ◽  
Stress Ratio ◽  
Chromic Acid ◽  
Fatigue Behavior ◽  
Fatigue Tests ◽  
Constant Amplitude ◽  
Aluminum Oxide Layer ◽  
Fatigue Life Reduction ◽  
Selection Of ◽  
Scanning Electron

Abstract The effect of chromic acid anodizing (CAA) surface treatment on 7050 T7451 aluminum alloy was presented in this study in terms of fatigue behavior. CAA is a treatment against corrosion by producing aluminum oxide layer (Al2O3) at the surface. However, fatigue performance of 7050 T7451 is affected by the coating. In this study, eight different CAA processes were examined with regard to etching stage of pre-treatments by using an alkaline etchant and/or acid etchants with various immersion times. Optical microscopic examinations were applied in order to determine pitting characteristics for the selection of CAA process parameters before fatigue tests. A CAA process was selected among eight processes in terms of pitting characteristics in order to apply fatigue specimens. Four fatigue test groups were determined to investigate bare condition of 7050 T7451 and sub-stages of the CAA particularly. Constant amplitude axial fatigue tests were conducted on specimens at 91 Hz at stress ratio (R) -1 until run-out criteria, which was 106 cycles. Fatigue life reduction was determined due to pretreatments of CAA. Fracture surfaces of the specimens were examined by scanning electron microscope (SEM) to investigate morphology and crack initiation sites.

scholarly journals Characterization of fatigue failed aged Cu-Ni-Si alloys

2018 ◽  
Vol 188 ◽  
pp. 02011
Author(s):  
Ş. Hakan Atapek ◽  
Spiros G. Pantelakis ◽  
Apostolos N. Chamos ◽  
Gülşah Aktaş Çelik
Keyword(s):  
Applied Stress ◽  
Stress Ratio ◽  
Crack Nucleation ◽  
High Strength ◽  
Fatigue Tests ◽  
Constant Amplitude ◽  
Lower Stress ◽  
Stress Levels ◽  
Lower Stress Level

The precipitation hardenable and non-toxic Cu-Ni-Si alloys are good alternatives to Cu-Be and Cu-Co-Ni-Be alloys due to their high strength and high conductivity that can be attained by not only alloying but also thermo-mechanical routes. In this study, the fractographic analysis was carried out to understand the fatigue failure of aged 2.55Ni-0.55Si-0.25Zr-0.25Cr (wt-%) alloy which is a member of Corson family. In fatigue tests, a constant amplitude loading was applied at a stress ratio (R = σmin/σmax) of -1 and different stress levels (400, 350, 200 and 175 MPa) were used. The fracture response of the alloy was discussed depending on the applied stress levels and microstructural features. It was concluded that (i) Ni,Zr-rich precipitates and Cr-rich precipitates at the grain boundaries caused crack nucleation at all stress levels and (ii) the interaction between Ni-rich silicides and dislocations at lower stress level resulted in localized shearing and fine striations.

scholarly journals Fatigue durability of asphalt-cement mixtures

2015 ◽  
Vol 63 (1) ◽  
pp. 107-111 ◽  
Author(s):  
J. Kuźniewski ◽  
Ł. Skotnicki ◽  
A. Szydło
Keyword(s):  
Fatigue Damage ◽  
Load Cycle ◽  
Fatigue Tests ◽  
Design Criterion ◽  
Asphalt Cement ◽  
Road Pavement ◽  
Fatigue Design ◽  
Fatigue Durability ◽  
Fatigue Design Criterion ◽  
Cement Mixtures

Abstract This paper focuses on examinations of asphalt-cement mixtures (ACM). This is a recycled material which can be used in road pavement layers. In the article stiffness modulus tests and fatigue tests of asphalt-cement mixtures were shown. The authors decided to lead research on fatigue durability of asphalt-cement mixtures to set fatigue characteristics of these materials. So far in research or other works any adequate fatigue criterion for ACM mixtures has not been developed. As a result of the examinations a level of fatigue damage was suggested. For new fatigue damage a strain level in one million load cycle was estimated. Based on that a fatigue design criterion for asphalt-cement mixtures was estimated.

Fatigue Tests and Design of Offshore Tubular Joints

1983 ◽  
Vol 105 (2) ◽  
pp. 189-194
Author(s):  
D. Dutta ◽  
F. Mang
Keyword(s):  
Stress Ratio ◽  
Design Method ◽  
Fatigue Behavior ◽  
Load Cycle ◽  
Fatigue Tests ◽  
Post Weld Heat Treatment ◽  
Small Scale ◽  
Plate Test ◽  
Tubular Joints ◽  
Stress Load

The AWS-X “hotspot stress-load cycle” curve used at present for designing tubular joints is based mainly on the fillet-welded plate test data and some more data from small-scale tests on tubular joints, which were available in the early 1970s. A review of further tests carried out in the recent years, including those by the authors, leads to the conclusion that the influence of the diameter and thickness of the tubes plays a significant role in the joint fatigue behavior. Hence, they must be taken into consideration while designing tubular joints accurately and more economically. A modified design method is proposed here with design curves for four diameter values. Further, the results of fatigue tests on K-type joints investigating the effect of stress ratio R and of post-weld heat treatment on the joint fatigue strength are described in this paper.

scholarly journals Fatigue strength of austempered ductile iron-to-steel dissimilar arc-welded joints

2021 ◽  
Author(s):  
G. Meneghetti ◽  
A. Campagnolo ◽  
D. Berto ◽  
E. Pullin ◽  
S. Masaggia
Keyword(s):  
Fatigue Strength ◽  
Ductile Iron ◽  
Welded Joints ◽  
Crack Nucleation ◽  
Fatigue Tests ◽  
International Standards ◽  
Austempered Ductile Iron ◽  
Metallographic Analysis ◽  
Fatigue Crack Nucleation ◽  
Selection Of

AbstractNowadays, the use of different classes of materials in the same structure is increased to keep pace with innovation and high structural performances. In this context, structural components made of different materials need to be joined together and a possible solution is given by arc welding. Dissimilar welded joints must often be able to withstand fatigue loads; however, Design Standards provide fatigue strength categories only for homogeneous welded joints. The aim of the present paper is to compare the fatigue behaviour of EN-GJS-1050 austempered ductile iron-to-S355J2 steel dissimilar joints to the categories of the corresponding homogeneous steel welded joints, as suggested in International Standards and Recommendations. For this purpose, experimental fatigue tests were performed on a selection of dissimilar welded details. First, the microstructure was identified by metallographic analysis; micro-hardness measurements were collected and residual stress profiles were obtained by using the X-ray diffraction technique on a selection of joints. Misalignments were quantified for all specimens. Then, experimental fatigue tests have been performed on a number of joint geometries subject to axial or bending fatigue loadings and tested in the as-welded conditions. The fracture surfaces of the joints have been analysed to locate fatigue crack nucleation sites.

Study of Initial Stages of Fatigue Process in Selective Laser Melting Material Using Acoustic Emission Method

2016 ◽  
Vol 258 ◽  
pp. 477-480
Author(s):  
Vendula Kratochvilova ◽  
Lucie Zemanova ◽  
František Vlasic ◽  
Pavel Mazal
Keyword(s):  
Acoustic Emission ◽  
Selective Laser Melting ◽  
Crack Nucleation ◽  
Fatigue Loading ◽  
Fatigue Tests ◽  
Acoustic Emission Method ◽  
Laser Melting ◽  
Emission Method ◽  
Fatigue Process ◽  
Wide Range

This paper deals with the evaluation of the fatigue tests and subsequent analyses of damage processes in selective laser melting (SLM) materials under bending loading. Compared to conventional production technologies (casting, forming and machining), SLM offers a wide range of benefits, e.g. production with no need for expensive molds, very low material waste and the possibility to create complex geometric shapes. The acoustic emission method was used to fully understand the processes which appear in the stages preceding the crack initiation. The fatigue tests at room temperature were conducted on standard wrought 2618A aluminium alloy as a representative testing material and the same material created by SLM. The main aim of the study was to compare the acoustic emission signal during fatigue loading at different manufacturing parameters of SLM material and to analyze in detail the signal changes in initial stages of fatigue process. The results show the high sensitivity of the acoustic emission technique to the fracture behaviour of SLM material and transition from the stage of surface relief evolution to the stage of crack nucleation and propagation. After completion of dynamic mechanical tests, a detailed fractographic analysis was conducted to assess material response to mechanical loading. Attention was focused on determining the predominant failure mechanisms and the influence of defects or inhomogeneities such as pores, cavities, etc. resulting from the production of materials using SLM method.

Flexural Fatigue of PVC Foams

2001 ◽  
Author(s):  
Krishnan Kanny ◽  
Hassan Mahfuz ◽  
Leif A. Carlsson ◽  
Tonnia Thomas ◽  
Shaik Jeelani
Keyword(s):  
Stress Ratio ◽  
Fatigue Behavior ◽  
Damping Ratio ◽  
Fatigue Tests ◽  
Foam Density ◽  
Flexural Fatigue ◽  
Viscoelastic Parameters ◽  
Final Failure ◽  
Failure Event ◽  
Sem Analyses

Abstract Flexural fatigue tests were performed on cross-linked PVC foams of densities in the range from 75 to 300 kg/m3 at a frequency of 3Hz and at a stress ratio, R = 0.1. S-N diagrams were generated, and the failure mechanisms were examined. The fatigue behavior was found to be similar to structural materials with a fatigue strength that decreased with increased stress and increased with increased foam density. The final failure event was catastrophic due to crack propagation initiating at the tension side of the beam. SEM analyses of unfailed and failed 300kg/m3 density foam specimens revealed cell wall cracking and densification of the foam. The densification contributed to stiffening of foam specimens. Viscoelastic parameters of the foams were determined at room temperature using a Dynamic Mechanical Analyzer (DMA) over a frequency range of 1–10Hz. For the virgin specimens it was found that the viscoelastic moduli and damping ratio were quite independent of frequency over this range of frequencies. Except for the lowest density foam (75kg/m3), the damping ratio was quite independent of foam density.

Selection of one-dimensional sedimentation: models for on-line use

1995 ◽  
Vol 31 (2) ◽  
pp. 193-204 ◽  
Author(s):  
Koen Grijspeerdt ◽  
Peter Vanrolleghem ◽  
Willy Verstraete
Keyword(s):  
Steady State ◽  
Selection Criteria ◽  
Data Sets ◽  
Concentration Profiles ◽  
A Posteriori ◽  
One Dimensional ◽  
On Line ◽  
Dynamic Concentration ◽  
Selection Of ◽  
Modelling Task

A comparative study of several recently proposed one-dimensional sedimentation models has been made. This has been achieved by fitting these models to steady-state and dynamic concentration profiles obtained in a down-scaled secondary decanter. The models were evaluated with several a posteriori model selection criteria. Since the purpose of the modelling task is to do on-line simulations, the calculation time was used as one of the selection criteria. Finally, the practical identifiability of the models for the available data sets was also investigated. It could be concluded that the model of Takács et al. (1991) gave the most reliable results.

scholarly journals ProReal®: The ‘good enough’ online alternative to face-to-face Dramatherapy

Dramatherapy ◽  
2021 ◽  
pp. 026306722110208
Author(s):  
Claire Anne Quigley
Keyword(s):  
Ambiguity Tolerance ◽  
Face To Face ◽  
On Line ◽  
And Control ◽  
Selection Of

The Covid-19 restrictions have limited the access of face-to face therapies for many people and continues to effect how Dramatherapists operate. The following article offers reflections around adapting to an on-line medium, focusing more specifically around the software of ProReal. Limitations and considerations are acknowledged, including technological difficulties, computer efficacy, ambiguity tolerance and the need for careful contracting and reassurance of autonomy and control when using on-line platforms. The article ends with a short selection of vignettes from ProReal sessions.

scholarly journals Acoustic Emission Testing and Ib-Value Analysis of Ultraviolet Light-Irradiated Fiber Composites

2021 ◽  
Vol 11 (14) ◽  
pp. 6550
Author(s):  
Doyun Jung ◽  
Wonjin Na
Keyword(s):  
Acoustic Emission ◽  
Irradiation Time ◽  
Tensile Load ◽  
Failure Behavior ◽  
Value Analysis ◽  
Emission Testing ◽  
Final Failure ◽  
Acoustic Emission Testing ◽  
Woven Glass Fiber ◽  
Ae Signals

The failure behavior of composites under ultraviolet (UV) irradiation was investigated by acoustic emission (AE) testing and Ib-value analysis. AE signals were acquired from woven glass fiber/epoxy specimens tested under tensile load. Cracks initiated earlier in UV-irradiated specimens, with a higher crack growth rate in comparison to the pristine specimen. In the UV-degraded specimen, a serrated fracture surface appeared due to surface hardening and damaged interfaces. All specimens displayed a linearly decreasing trend in Ib-values with an increasing irradiation time, reaching the same value at final failure even when the starting values were different.

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