A coupled poroplastic damage model accounting for cracking effects on both hydraulic and mechanical properties of unsaturated media

2015 ◽  
Vol 40 (5) ◽  
pp. 625-650 ◽  
Author(s):  
Tuan Anh Bui ◽  
Henry Wong ◽  
Frederic Deleruyelle ◽  
Annan Zhou ◽  
Xiaoqin Lei
Keyword(s):  
Mechanical Properties ◽  
Damage Model ◽  
Unsaturated Media

Simulation of Nano- and Micro-Indentation Behavior of Bone via a Plastic-Damage Model

2008 ◽  
Author(s):  
Jingzhou Zhang ◽  
Timothy Ovaert
Keyword(s):  
Mechanical Properties ◽  
Damage Model ◽  
Maximum Load ◽  
High Load ◽  
Material Degradation ◽  
Bone Specimen ◽  
Naturally Occurring ◽  
Plastic Damage ◽  
Indent Depth ◽  
Micro Indentation

Damage results in a loss of material continuity, which distinguishes it from other types of material degradation. The loss of continuity can have an adverse effect on mechanical properties, and may be manifested in the form of cracks and/or voids. Bone tissue, as a composite material, contains voids and other non-homogeneities that are naturally occurring and distinct from damage. However, when subjected to mechanical loading, such as indentation, further damage accumulation may occur. Figure 1 shows a cross-section of a bovine cortical bone specimen after high-load conical indentation to a depth of 300 μm, resulting in a large permanently deformed region. Nanoindentation, using a Berkovich tip at 10 mN maximum load, was then performed at numerous locations within three defined damage “zones”. Zone 1 is adjacent to the bottom of the indent, defined at 25% of the maximum indent depth. Zones 2 and 3 extend further away, both scaled as a function of the indentation depth, d. Figure 2 shows the variation in Young’s modulus in the three damage zones, averaged over approximately 25 indents per zone. The data suggest that local changes in mechanical properties may occur as a result of compaction of voids or cracks. The purpose of this work, therefore, is to investigate the application of a plastic-damage model for simulation of bone nano- and micro-scale indentation behavior.

The Precise Determination of the Johnson–Cook Material and Damage Model Parameters and Mechanical Properties of an Aluminum 7068-T651 Alloy

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
B. Bal ◽  
K. K. Karaveli ◽  
B. Cetin ◽  
B. Gumus
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Physical Simulation ◽  
Damage Model ◽  
Rolling Direction ◽  
Stress Triaxiality ◽  
Material Model ◽  
Tensile Tests ◽  
Model Parameters ◽  
Element Analysis

Al 7068-T651 alloy is one of the recently developed materials used mostly in the defense industry due to its high strength, toughness, and low weight compared to steels. The aim of this study is to identify the Johnson–Cook (J–C) material model parameters, the accurate Johnson–Cook (J–C) damage parameters, D1, D2, and D3 of the Al 7068-T651 alloy for finite element analysis-based simulation techniques, together with other damage parameters, D4 and D5. In order to determine D1, D2, and D3, tensile tests were conducted on notched and smooth specimens at medium strain rate, 100 s−1, and tests were repeated seven times to ensure the consistency of the results both in the rolling direction and perpendicular to the rolling direction. To determine D4 and D5 further, tensile tests were conducted on specimens at high strain rate (102 s−1) and temperature (300 °C) by means of the Gleeble thermal–mechanical physical simulation system. The final areas of fractured specimens were calculated through optical microscopy. The effects of stress triaxiality factor, rolling direction, strain rate, and temperature on the mechanical properties of the Al 7068-T651 alloy were also investigated. Damage parameters were calculated via the Levenberg–Marquardt optimization method. From all the aforementioned experimental work, J–C material model parameters were determined. In this article, J–C damage model constants, based on maximum and minimum equivalent strain values, were also reported which can be utilized for the simulation of different applications.

scholarly journals Study on Damage Model and Damage Evolution Characteristics of Backfill with Prefabricated Fracture under Seepage-Stress Coupling

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Jifeng Hou ◽  
Zhongping Guo ◽  
Weizhen Liu ◽  
Hengze Yang ◽  
WenWu Xie
Keyword(s):  
Mechanical Properties ◽  
Damage Evolution ◽  
Coupling Effect ◽  
Water Pressure ◽  
Damage Model ◽  
Confining Pressure ◽  
Seepage Water ◽  
Confining Pressures ◽  
Initial Fracture ◽  
Total Damage

Aiming at the backfill with prefabricated fracture under seepage-stress coupling, the concepts of fracture macrodamage, loaded mesodamage, seepage mesodamage, and total damage of backfill were proposed. Based on the macroscopic statistical damage model, the coupling effect of seepage, stress, and initial fracture was considered comprehensively and the damage model of backfill with prefabricated fracture under seepage-stress coupling was established. The mechanical properties of backfill with prefabricated fracture under different seepage water pressures and confining pressures were tested and the rationality of the model was verified. The research shows that the mechanical properties of backfill with prefabricated fracture under the seepage-stress coupling are determined by the seepage water pressure, the load, the initial fracture, and the coupling effect. Fracture and seepage have significant effects on the damage of the backfill. When the seepage water pressure is low, the fracture damage dominates; however, when the seepage water pressure is high, the seepage damage dominates; the total damage under the coupling action is more serious than the single factor. The development laws of the total damage evolution curves under different seepage water pressures and confining pressures are basically the same, and they show the S-shaped distribution law with the increase of the axial strain. With the increase of confining pressure, the damage effect of fracture and seepage on the backfill is weakened, indicating that the confining pressure has a certain inhibitory effect on the damage evolution of the backfill. The research results can provide a theoretical basis for the study of the stability of backfill with geological defects such as joints and fractures in deep high-stress and high-seepage water pressure coal mines.

Damage Model and Damage Mechanical Characteristics of Loaded Rock under Freeze-Thaw Conditions

2010 ◽  
Vol 168-170 ◽  
pp. 658-662 ◽  
Author(s):  
Hui Mei Zhang ◽  
Geng She Yang
Keyword(s):  
Mechanical Properties ◽  
Structural Damage ◽  
Damage Mechanics ◽  
Coupling Effect ◽  
Damage Model ◽  
Engineering Structures ◽  
Freeze Thaw ◽  
Thaw Cycle ◽  
Loaded Rock ◽  
Total Damage

Considering the heterogeneous characteristics of rock at mesoscopic level, the damage propagation constitutive relation and evolution equation of freeze-thaw and loaded rock were established by using the theory of macro phenomenological damage mechanics and the generalized theory of strain equality. The evolutionary mechanisms of micro-structural damage and materials mechanical properties for the loaded rock were discussed under freeze-thaw condition, verified by experimental results of the freeze-thaw cycle and compression test of rock. It is shown that the freeze-thaw and loaded damage model can represent the complicated relations among the freeze-thaw, load and the damage inside the rock, reveal the coupling failure mechanism of macroscopic rock under the freeze-thaw and load from the micro-damage evolution. The combined effect of freeze-thaw and load exacerbates the total damage of rock with obvious nonlinear properties, but the coupling effect weakens the total damage. The lithology and initial damage state of the freeze-thaw and loaded rock in engineering structures in cold regions determine the weights of influence factors to mechanical properties, including environmental factor, loading factor and the coupling effects, so the rock performances different damage mechanical characteristic.

Prediction of Ductile Crack Growth from Ductility of Steel

2007 ◽  
Vol 539-543 ◽  
pp. 2186-2191 ◽  
Author(s):  
Mitsuru Ohata ◽  
Takuya Fukahori ◽  
Fumiyoshi Minami
Keyword(s):  
Mechanical Properties ◽  
Crack Initiation ◽  
Crack Growth ◽  
Damage Model ◽  
Stress Triaxiality ◽  
Local Strain ◽  
Strength Properties ◽  
Ductile Crack ◽  
Ductile Crack Growth ◽  
Point Bend

This study pays attention to reveal the material properties that control resistance curve for ductile crack growth (CTOD-R curve) on the basis of the mechanism for ductile crack growth, so that the R-curve could be numerically predicted only from those properties. The crack growth tests using 3-point bend specimens with fatigue pre-crack were conducted for two steels that have different ductile crack growth resistance with almost the same CTOD level for crack initiation, whereas both steels have the same “Mechanical properties” in terms of strength and work hardenability. The observation of crack growth behaviors provided that different mechanisms between ductile crack initiations from fatigue pre-crack and subsequent growth process could be applied. It was found that two “Mechanical properties” associated with ductile damage of steel could mainly influence CTOD-R curve; one is a resistance of ductile crack initiation estimated with critical local strain for ductile cracking from the surface of notched specimen, and the other one is a dependence of stress triaxiality on ductility obtained with circumferentially notched round-bar specimens. The damage model for numerically simulating the R-curve was proposed taking the two “ductile properties” into account, where ductile crack initiation from crack-tip was in accordance with critical local strain based criterion, and subsequent crack growth GTN (Gurson-Tvergaard-Needleman) based triaxiality dependent damage criterion. The proposed model accurately predicted the measured R-curve for the two steels used with the same “strength properties” through ductile crack initiation to growth.

Effect of preload and shim types on the mechanical properties of composite-aluminium bolted joints

2021 ◽  
pp. 095440622110071
Author(s):  
Xuande Yue ◽  
Luling An ◽  
Zengtao Chen ◽  
Yuebo Cai ◽  
Chufan Wang
Keyword(s):  
Mechanical Properties ◽  
Composite Laminates ◽  
Damage Model ◽  
Peak Load ◽  
Lap Joints ◽  
Surface Strain ◽  
Displacement Curve ◽  
Progressive Damage ◽  
Single Lap Joints ◽  
Tensile Stiffness

The influence of both preload and the presence of shim types on the mechanical properties of composite-aluminium single-bolt, single-lap joints were studied in this paper. The load-displacement curve and surface strain field of joints in different shim types and preloads were obtained through tensile experiments. A progressive damage model was established using the UMAT subroutine in ABAQUS. A hybrid failure criterion and a linear continuous degradation model were used to describe the progressive damage of composite laminates. The results show that for joints with no shim and for those with various types of shims, the tensile stiffness, peak load and initial damage load could be reduced when the preload is insufficient or too large. Compared with joints with no shims or with peelable fibreglass shims, joints with liquid shims required a larger preload to achieve the best mechanical properties. As the proportion of peelable fibreglass shim increased, the tensile stiffness and peak load continued to increase in joints with a mixed shim of liquid and peelable fiberglass shim. Shims can serve as tension bearings, but have little effect on the initiation and development of bearing failure.

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