Internal Stress
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Guowei Zhou ◽  
David T Fullwood ◽  
Jay Carroll ◽  
Eric Homer ◽  
Hojun Lim ◽  

Abstract Yield point phenomena (YPP) are widely attributed to discrete dislocation locking by solute atmospheres. An alternate YPP mechanism was recently suggested by simulations of Ta single crystals without any influence of solutes or discrete dislocations. The general meso-scale (GM) simulations consists of crystal plasticity (CP) plus accounting for internal stresses of geometrically necessary dislocation content. GM predicted the YPP while CP did not, suggesting a novel internal stress mechanism. The predicted YPP varied with crystal orientation and boundary conditions, contrary to expectations for a solute mechanism. The internal stress mechanism was probed by experimentally deforming oligocrystal Ta samples and comparing the results with independent GM simulations. Strain distributions of the experiments were observed with high-resolution digital image correlation. A YPP stress-strain response occurred in the 0-2% strain range in agreement with GM predictions. Shear bands appeared concurrent with the YPP stress-strain perturbation in agreement with GM predictions. At higher strains, the shear bands grew at progressively slower rates in agreement with GM predictions. It was concluded that the internal stress mechanism can account for the existence of YPP in a wide variety of materials including ones where interstitial-dislocation interactions and dislocation transient avalanches are improbable. The internal stress mechanism is a crystal plasticity analog of various micro-scale mechanisms of discrete dislocations such as pile-up or bow-out. It may operate concurrently with strain aging, or either mechanism may operate alone. A suggestion was made for a future experiment to answer this question.

2021 ◽  
Vol 7 (7) ◽  
pp. 106
Jiewei Zeng ◽  
Yunsong Xu ◽  
Shi Liang ◽  
Zhiqiang Long

In order to meet the technical requirements of non-destructive measurement for the internal stress of ferromagnetic materials represented by cold-rolled steel sheets during the rolling control process, the paper presents a novel method for the nondestructive measurement of ferromagnetic materials based on inverse magnetostrictive principle. By improving the traditional U-shaped sensor, a transmissive quadrapole layout is proposed. The corresponding excitation module and fast signal processing system for dynamic measurement were developed and the test system for detecting innerstress of ferromagnetic material was constructed in the laboratory. The relationship between the magnetic flux with the principal stress was found by experimental investigation and the sensitive correlation of the two was verified under the laboratory measurement conditions without strong electromagnetic interference. The influence of measurement results by sensor parameters such as sensor angle, amplitude of excitation current, variation of air gap were discussed in detail and a method was proposed to decrease the power supply instability caused by the change of the airgap. The experimental results show that the transmission quadrupole layout makes the test system exhibit a good linear response to the internal stress in the specimen. The feasibility of the magnetic detection method of internal stresses in ferromagnetic material was verified through the experiment.

2021 ◽  
Vol 15 (4) ◽  
pp. 483-491
Soshi Iwatsuki ◽  
Hirofumi Hidai ◽  
Souta Matsusaka ◽  
Akira Chiba ◽  
Noboru Morita ◽  

In laser cleaving, the thermal stress caused by laser heating and water-jet cooling propagates previously induced cracks in the workpiece material. The laser-cleaving conditions affect the quality of the fracture surface, and therefore, elucidating the relationship between the cleaved surface, cleaving conditions, and crack propagation is essential. Against this backdrop, in this study, we investigated the morphology of the cleaved surface and visualized the crack propagation and stress in situ using a high-speed polarization camera. The distance between the glass edge and cleaved surface was varied. When the laser-cleavage line was close to the glass edge, twist hackles were formed on the cleaved surface. The area in which the twist hackles formed on the cleaved surface coincided with the lagging section of the crack front. Furthermore, the twist hackle reached the specimen surface, and the edge of the surface exhibited a sawtooth shape. Observations with the high-speed polarization camera revealed that the internal stress was asymmetric with respect to the crack when the twist hackles were formed.

2021 ◽  
Vol 119 (1) ◽  
pp. 013502
Kouji Suemori ◽  
Nobuki Ibaraki ◽  
Toshihide Kamata

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Ai Chen

Reasonable width of gob-side coal pillar can reduce the waste of coal resources and is conducive to roadway stability. According to the distribution of internal and external stress fields at the working face, a method for determining the width of gob-side coal pillar was proposed. The coal pillar and roadway should be set within the internal stress field, and support is provided through the anchored part and the intact part of the coal pillar. The method was used in the design of the coal pillar at No. 130205 working face of Zaoquan Coal Mine. The calculation results indicated that the width of a coal pillar suitable for gob-side entry is 6.0 m. It is reasonable to arrange the roadway and coal pillar in the low-stress zone with a width of 11 m. During tunnelling of roadway and stoping of the working face, the deformation of the roadway increased with a reduction in the distance from the working face. Even during stoping of the working face, there was an approximately 1.5 m intact zone in the coal pillar. This indicates that the proposed method of designing small coal pillar of gob-side entry driving is reliable.

2021 ◽  
V. Sakthi Murugan ◽  
S. Madhu

Abstract The Silicon (Si) contained diamond like carbon (DLC) nanocomposite were prepared by using thermal chemical vapour deposition (CVD) technique by varying the acetylene (C2H2) flowrates. The scanning electron microscope (SEM) results showed a smoother surface of nanocomposite at low C2H2 flowrates. The atomic force microscope (AFM) reveals the increase of particle size and surface roughness of the composite with respect to the C2H2 flowrates. The mechanical properties were evaluated using the nanoindentation and it is observed that the hardness (H) and young’s modulus (E) of the nanocomposite increases with increase of the C2H2 flow rate. The internal stress (𝝈) was computed by using Stoney’s equation and it is noticed that due to the incorporation of Si the residual stress significantly decreased. The tribological properties of the nanocomposite were analysed by computing the H/E, H3/E2, plasticity index (PI) and elasticity index (EI). The results showed that the Si incorporated nanocomposite (Si-DLC) has an excellent tribological properties.

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