Microcrack propagation under non-proportional multiaxial alternating loading

2003 ◽  
pp. 441-460 ◽  
Author(s):  
Matthias Weick ◽  
Jarir Aktaa
Keyword(s):  
Microcrack Propagation

scholarly journals Investigation of Microcrack Propagation and Energy Evolution in Brittle Rocks Based on the Voronoi Model

Materials ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2108
Author(s):  
Guanlin Liu ◽  
Youliang Chen ◽  
Xi Du ◽  
Peng Xiao ◽  
Shaoming Liao ◽  
...  
Keyword(s):  
Uniaxial Compression ◽  
Damage Evolution ◽  
Rock Sample ◽  
Rock Fracture ◽  
Damage Threshold ◽  
Crack Development ◽  
Energy Evolution ◽  
Shear Cracks ◽  
Compression Tests ◽  
Microcrack Propagation

The cracking of rock mass under compression is the main factor causing structural failure. Therefore, it is very crucial to establish a rock damage evolution model to investigate the crack development process and reveal the failure and instability mechanism of rock under load. In this study, four different strength types of rock samples from hard to weak were selected, and the Voronoi method was used to perform and analyze uniaxial compression tests and the fracture process. The change characteristics of the number, angle, and length of cracks in the process of rock failure and instability were obtained. Three laws of crack development, damage evolution, and energy evolution were analyzed. The main conclusions are as follows. (1) The rock’s initial damage is mainly caused by tensile cracks, and the rapid growth of shear cracks after exceeding the damage threshold indicates that the rock is about to be a failure. The development of micro-cracks is mainly concentrated on the diagonal of the rock sample and gradually expands to the middle along the two ends of the diagonal. (2) The identification point of failure precursor information in Acoustic Emission (AE) can effectively provide a safety warning for the development of rock fracture. (3) The uniaxial compression damage constitutive equation of the rock sample with the crack length as the parameter is established, which can better reflect the damage evolution characteristics of the rock sample. (4) Tensile crack requires low energy consumption and energy dispersion is not concentrated. The damage is not apparent. Shear cracks are concentrated and consume a large amount of energy, resulting in strong damage and making it easy to form macro-cracks.

scholarly journals Rapid Consolidation of WC-ZrSiO4 Hard Materials by Spark Plasma Sintering: Microstructure, Densification, and Mechanical Properties

2021 ◽  
Author(s):  
Jeong-Han Lee ◽  
Ik-Hyun Oh ◽  
Ju-Hun Kim ◽  
Sung-Kil Hong ◽  
Hyun-Kuk Park
Keyword(s):  
Mechanical Properties ◽  
Spark Plasma Sintering ◽  
Lattice Distortion ◽  
Hard Materials ◽  
Plasma Sintering ◽  
Microcrack Propagation ◽  
Spark Plasma ◽  
Crack Tips ◽  
Ductile Component ◽  
Constant Heating

Abstract Densely consolidated WC-based hard materials with 5–20 vol% ZrSiO4 was fabricated by spark plasma sintering at 1400 ℃ at a constant heating rate of 70 ℃/min−1. To achieve mechanical alloying of WC-ZrSiO4, planetary ball milling was carried out for 12 h, during which the brittle-brittle components (WC-ZrSiO4) became fragmented and their particles became refined. It was observed that certain, specific, non-isothermal sintering kinetics, such as apparent activation energy, sintering exponents, and densification strain, affected the densification behavior. The evolution of phase structure from powder to compact was found to be related the lattice distortion and micro-strain in the basal planes of WC. By examining the mechanical properties of the samples, it was that the added zircon content leads to enhanced fracture toughness (12.9 MPa m1/2) owing to the presence of WC-ZrSiO4 in the cemented carbide. In fact, the microcrack propagation of the fracture passed through zircon from a transgranular to a ductile component (fcc) where the crack tips could be absorbed. Graphic Abstract

scholarly journals Effect of Electric Current Pulse on Microstructure and Corrosion Resistance of Hypereutectic High Chromium Cast Iron

Materials ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2220 ◽  
Author(s):  
Haiyang Lv ◽  
Rongfeng Zhou ◽  
Lu Li ◽  
Haitao Ni ◽  
Jiang Zhu ◽  
...  
Keyword(s):  
Corrosion Resistance ◽  
Cast Iron ◽  
Electric Current ◽  
Current Pulse ◽  
Electric Current Pulse ◽  
High Chromium ◽  
High Chromium Cast Iron ◽  
Microcrack Propagation ◽  
Primary Carbides ◽  
Chromium Cast Iron

The effect of electric current pulse on the microstructure and corrosion resistance of hypereutectic high chromium cast iron was explored. The morphology of carbides in solidification microstructure was observed by an optical microscope and a scanning electron microscope and the composition was determined by an electron probe micro-analyzer. The microhardness of primary carbides and corrosion resistance of samples were also compared. Under the active of electric current pulse, the microstructure of hypereutectic high chromium cast iron was homogenized and its performance improved accordingly. On treatment by electric current, the morphology of primary carbides changed from thick long rods to hexagonal blocks or granular structures. The interlayer spacing of eutectic carbide decreased from ~26.3 μm to ~17.8 μm. Size statistics showed that the average diameter of primary carbide decreased from ~220 μm to ~60 μm. As a result, microhardness increased from 1412 HV to 1511 HV. No obvious microcrack propagation was found at the microindentation sites. The average length of microcracks decreased from ~20.7 μm to ~5.7 μm. Furthermore, corrosion resistance was remarkably enhanced. The average corrosion rate decreased from 2.65 mg/cm2·h to 1.74 mg/cm2·h after pulse current treatment.

A Creep-Fatigue-Oxidation Microcrack Propagation Model for Thermomechanical Fatigue

1992 ◽  
Vol 114 (3) ◽  
pp. 282-288 ◽  
Author(s):  
M. P. Miller ◽  
D. L. McDowell ◽  
R. L. T. Oehmke
Keyword(s):  
Mechanical Strain ◽  
Thermomechanical Fatigue ◽  
Propagation Model ◽  
Additional Time ◽  
Basic Model ◽  
Proposed Model ◽  
Microcrack Propagation ◽  
Creep Fatigue ◽  
Phase Out ◽  
Model Features

A high temperature fatigue (HTF) life prediction model is developed based on the concept of microcrack propagation. The model is used to correlate isothermal HTF and thermomechanical fatigue (TMF) life for the Ni-base superalloy MAR-M247. The mechanical strain versus temperature relationships for the TMF tests include in-phase, out-of-phase, and a counter-clockwise diamond history. The proposed model explicitly accounts for damage from all three HTF damage mechanisms: fatigue, oxidation, and creep. The fatigue and oxidation components are correlated using the ΔJ parameter with an additional time dependence included in the oxidation term. The creep component is correlated using a stress power release rate-type parameter, Cˆ. In this paper, we focus on application of a model to HTF and TMF of Ni-base superalloys. However, the basic model features may well apply to other classes of metallic materials.

Sign in / Sign up

Export Citation Format

Share Document