scholarly journals Linking permeability to crack density evolution in thermally stressed rocks under cyclic loading

2013 ◽  
Vol 40 (11) ◽  
pp. 2590-2595 ◽  
Author(s):  
I. Faoro ◽  
S. Vinciguerra ◽  
C. Marone ◽  
D. Elsworth ◽  
A. Schubnel
Keyword(s):  
Cyclic Loading ◽  
Crack Density ◽  
Density Evolution ◽  
Thermally Stressed

A Dislocation Density Based Constitutive Model for Cyclic Deformation

1996 ◽  
Vol 118 (4) ◽  
pp. 441-447 ◽  
Author(s):  
Y. Estrin ◽  
H. Braasch ◽  
Y. Brechet
Keyword(s):  
Cyclic Loading ◽  
Dislocation Density ◽  
Constitutive Model ◽  
Constitutive Equations ◽  
Cyclic Deformation ◽  
Internal Variables ◽  
Density Evolution ◽  
Alloy 800H ◽  
Material Response ◽  
Dislocation Densities

A new constitutive model describing material response to cyclic loading is presented. The model includes dislocation densities as internal variables characterizing the microstructural state of the material. In the formulation of the constitutive equations, the dislocation density evolution resulting from interactions between dislocations in channel-like dislocation patterns is considered. The capabilities of the model are demonstrated for INCONEL 738 LC and Alloy 800H.

Study on Damage Progression Process for Plain-Woven Carbon Fabric Composites Under Cyclic Loading

2002 ◽  
Author(s):  
Y. Nishikawa ◽  
K. Okobo ◽  
T. Fujii
Keyword(s):  
Cyclic Loading ◽  
Unit Area ◽  
Crack Density ◽  
Fiber Bundles ◽  
Damage Analysis ◽  
Carbon Fabric ◽  
Transverse Fiber ◽  
Damage Progression ◽  
Fabric Composites ◽  
Three Stages

In this study, the damage progression process for plain-woven carbon fabric composites (PW-CFCs) under cyclic loading was investigated. Under cyclic loading, the damage progression was estimated intermittently by using the thermo-elastic damage analysis (TDA) method. Crack density for each layer of the specimen was also estimated at several stages of fatigue. It was found from these results that the damage progression process was divided into three stages. In the first stage, especially, the damage accumulation occurred independently in the PW-CFC specimen and progressed easily along the transverse fiber bundles. All experimental results showed that the damage progression in the first fatigue stage was explained by considering damage-units (a unit area of damage progression and accumulation). Based on the percolation theory, the damage progression for PW-CFC under cyclic loading can be characterized by re-generating the distribution pattern of damage-units.

scholarly journals Experimental Investigation of Sandstone under Cyclic Loading: Damage Assessment Using Ultrasonic Wave Velocities and Changes in Elastic Modulus

2018 ◽  
Vol 2018 ◽  
pp. 1-13 ◽  
Author(s):  
Sen Yang ◽  
Nong Zhang ◽  
Xiaowei Feng ◽  
Jiaguang Kan ◽  
Dongjiang Pan ◽  
...  
Keyword(s):  
Cyclic Loading ◽  
Damage Assessment ◽  
Crack Density ◽  
Density Parameter ◽  
Velocity Measurements ◽  
Ultrasonic Velocities ◽  
Damage Development ◽  
Irreversible Damage ◽  
Low Level ◽  
Wave Velocities

This laboratory study investigated the damage evolution of sandstone specimens under two types of cyclic loading by monitoring and analyzing changes in the elastic moduli and the ultrasonic velocities during loading. During low-level cyclic loading, the stiffness degradation method was unable to describe the damage accumulations but the ultrasonic velocity measurements clearly reflected the damage development. A crack density parameter is introduced in order to interpret the changes in the tangential modulus and the ultrasonic velocities. The results show the following. (1) Low-level cyclic loading enhanced the anisotropy of the cracks. This results from the compression of intergranular clay minerals and fatigue failure. (2) Irreversible damage accumulations during cyclic loading with an increasing upper stress limit are the consequence of brittle failure in the sandstone’s microstructure.

Characterization and Modelling of Multiple Intralaminar Cracking Initiation under Tensile Quasi-Static and Fatigue Loading

2018 ◽  
Vol 774 ◽  
pp. 467-472
Author(s):  
H. Ben-Kahla ◽  
Janis Varna
Keyword(s):  
Cyclic Loading ◽  
Fatigue Behavior ◽  
Crack Density ◽  
Fatigue Loading ◽  
Shear Stresses ◽  
Stress Concentrations ◽  
Density Region ◽  
Static Tests ◽  
Distribution Parameters ◽  
Intralaminar Cracking

The first failure mode in tensile quasi-static and in tension-tension fatigue (cyclic) loading of composite laminates is intralaminar cracking in layers with off-axis fiber orientation. These tunnel-building cracks are result of combined action of in-plane transverse and shear stresses. We assume that due to non-uniform fiber distribution (clustering) which leads to local stress concentrations, different positions in the layer have different resistance to crack initiation (initiation strength). If so, the weakest position in quasi-static loading is also the weakest in fatigue and some of the distribution parameters for fatigue behavior can be obtained in quasi-static tests, thus significantly reducing the number of required fatigue tests. Methodology is suggested and validated for cases when the cracking is initiation governed-initiated crack almost instantly propagates along fibers. Distribution parameters are identified using data in low crack density region where stress perturbations from cracks do not interact. Monte-Carlo simulations are performed for cracking in layers under quasi-static and cyclic loading using novel approach for computationally efficient stress state calculation between existing cracks.

scholarly journals The structural integrity of nanoclay filled epoxy polymer under cyclic loading

2017 ◽  
Author(s):  
◽  
Sathievelli Chetty
Keyword(s):  
Cyclic Loading ◽  
Crack Initiation ◽  
Fatigue Failure ◽  
Crack Density ◽  
Fatigue Crack Initiation ◽  
Fatigue Loading ◽  
Fatigue Cycle ◽  
Crack Initiation And Propagation ◽  
Initiation And Propagation ◽  
Number Of Cycles

Fatigue crack initiation and propagation behaviour of CFRP have been of great importance because such composites are often used in engineering components that are subjected to continuous cyclic loading. The objective of this thesis work was to investigate the damage characteristics of the fatigue properties of CFRP composites by the modification of the polymer matrix with nanoclay addition. Carbon fibre reinforced epoxy was produced via vacuum assisted resin infusion moulding method (VARIM) with nanoclay concentrations of 0wt%, 1wt%, 3wt% and 5wt%. Tension-tension fatigue tests were conducted at loading levels of 90%, 75% and 60%. The frequency that was used was 3Hz with R value of 0.1. The results showed that at nanoclay percentages of 0wt%, 1wt% and 3wt% there was a consistent trend, where the number of cycles increased in fatigue loading percentages of 90%, 75% and 60%. At 5wt% nanoclay percentage the number of fatigue cycles dropped significantly at the 90% fatigue loading. The brittle nature of the 5wt% laminate became dominate and the sample fractured early at low fatigue cycle numbers. At the 75% fatigue loading, the number of cycles increased and at 60% fatigue loading the 5wt% nanoclay sample exceeded the number of cycles of all the nanoclay percentages by 194%. This was due to the intercalated arrangement of the nanoclays favouring the slow rate of surface temperature increase, during fatigue testing, at low fatigue cycle loading. The Crack Density analysis was performed and showed that at the same time in the fatigue cycle life, the 1wt% had 55 cracks, 3wt% had 52 cracks and the 5wt% had 50 cracks, for the 60% fatigue loading. This proved that it took longer for the cracks to initiate and propagate through the sample as the nanoclay percentage increased. Impact and hardness testing showed that the 5wt% exhibited brittle behaviour, which contributed to the results above. Scanning electron microscopy examination highlighted that the agglomeration of nanoclays delayed the crack initiation and propagation through the specimen and that the extent of fatigue damage decreased as the nanoclay percentage increased. A fatigue failure matrix was developed and showed that delamination, fibre breakage and matrix failure were the predominate causes for the fatigue failure.

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