Effective Microstructure Unit in Control of Plasticity during Strain‐Controlled Fracture

2019 ◽  
Vol 90 (11) ◽  
pp. 1900140
Author(s):  
Shao-lei Long ◽  
Yi-long Liang ◽  
Min Lin ◽  
Ming Yang ◽  
Cun-hong Yin ◽  
...  
Keyword(s):  
Controlled Fracture

Mechanism of irregular crack-propagation in thermal controlled fracture of ceramics induced by microwave

2020 ◽  
Vol 21 (6) ◽  
pp. 610
Author(s):  
Xiaoliang Cheng ◽  
Chunyang Zhao ◽  
Hailong Wang ◽  
Yang Wang ◽  
Zhenlong Wang
Keyword(s):  
Crack Propagation ◽  
Industrial Application ◽  
Ceramic Materials ◽  
Advanced Technology ◽  
Analytical Models ◽  
Propagation Mechanism ◽  
Unstable Crack ◽  
Fracture Simulation ◽  
Initial Stage ◽  
Controlled Fracture

Microwave cutting glass and ceramics based on thermal controlled fracture method has gained much attention recently for its advantages in lower energy-consumption and higher efficiency than conventional processing method. However, the irregular crack-propagation is problematic in this procedure, which hinders the industrial application of this advanced technology. In this study, the irregular crack-propagation is summarized as the unstable propagation in the initial stage, the deviated propagation in the middle stage, and the non-penetrating propagation in the end segment based on experimental work. Method for predicting the unstable propagation in the initial stage has been developed by combining analytical models with thermal-fracture simulation. Experimental results show good agreement with the prediction results, and the relative deviation between them can be <5% in cutting of some ceramics. The mechanism of deviated propagation and the non-penetrating propagation have been revealed by simulation and theoretical analysis. Since this study provides effective methods to predict unstable crack-propagation in the initial stage and understand the irregular propagation mechanism in the whole crack-propagation stage in microwave cutting ceramics, it is of great significance to the industrial application of thermal controlled fracture method for cutting ceramic materials using microwave.

Hybrid CO2 Laser/Waterjet Machining of Polycrystalline Diamond Substrate: Material Separation Through Transformation Induced Controlled Fracture

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
Dinesh Kalyanasundaram ◽  
Andrea Schmidt ◽  
Pal Molian ◽  
Pranav Shrotriya
Keyword(s):  
Co2 Laser ◽  
Polycrystalline Diamond ◽  
Substrate Material ◽  
Stress Fields ◽  
Separation Mechanism ◽  
Raman Spectrometry ◽  
Waterjet Machining ◽  
Machining System ◽  
Material Separation ◽  
Controlled Fracture

This paper presents a combined experimental and computational investigation of a novel material separation mechanism in polycrystalline diamond (PCD) substrates. A hybrid CO2 laser/waterjet (CO2-LWJ) machining system that combines a CO2 laser for localized heating and an abrasive-free waterjet to rapidly quench the heated area is utilized for cutting experiments on PCD substrates. Scanning electron microscopy (SEM) and micro-Raman spectrometry characterization performed on the cut surfaces show that cut surfaces were divided into two zones—a thin transformed zone near the top where the PCD grains have transformed to graphite and diamond-like carbon; and a fracture zone with the same composition as-received substrate. The experimental results indicate that the PCD substrates were cut through a “score and snap” mechanism—laser heating leads to localized damage and phase transformation of surface layers; and subsequently, stress fields developed due to constrained expansion of transformed material and waterjet quenching act on the laser made “score” to propagate crack through the thickness. Analytical solutions for thermal diffusion and force equilibrium are used to determine the temperature and stress fields in the PCD substrate during CO2-LWJ cutting. Fracture mechanics analysis of crack propagation is performed to demonstrate the feasibility of the “score and snap” mechanism for cutting of PCD substrates.

Subcritical Delamination of Dielectric and Metal Films from Low-k Organosilicate Glass (OSG) Thin Films in Buffered pH Solutions

2003 ◽  
Vol 795 ◽  
Author(s):  
Y. Lin ◽  
J. J. Vlassak ◽  
T. Y. Tsui ◽  
A. J. McKerrow
Keyword(s):  
Thin Films ◽  
Ph Value ◽  
Dielectric Materials ◽  
Barrier Films ◽  
Interface Delamination ◽  
Organosilicate Glass ◽  
Controlled Fracture ◽  
Ph Buffer ◽  
Subcritical Fracture ◽  
Low K

ABSTRACTUnderstanding subcritical fracture of low-k dielectric materials and barrier thin films in buffered solutions of different pH value is of both technical and scientific importance. Subcritical delamination of dielectric and metal barrier films from low-k organosilicate glass (OSG) films in pH buffer solutions was studied in this work. Crack path and subcritical fracture behavior of OSG depends on the choice of barrier layers. For the OSG/TaN system, fracture takes place in the OSG layer near the interface, while in OSG/SiNx system, delamination occurs at the interface. Delamination behavior of both systems is well described by a hyperbolic sine model that had been developed previously based on a chemical reaction controlled fracture process at the crack tip. The threshold toughness of both systems decreases linearly with increasing pH value. The slopes of the reaction-controlled regime of the crack velocity curves for both systems are independent of pH as predicted by the model. Near transport-controlled regime behavior was observed in OSG/TaN system.

Regional Variability in Lithic Miniaturization and the Organization of Technology in Late Glacial Southern Africa (~18-11 kcal BP)

2020 ◽  
Vol 18 (1) ◽  
pp. 38-66 ◽  
Author(s):  
Marika Low ◽  
Justin Pargeter
Keyword(s):  
Southern Africa ◽  
Raw Materials ◽  
Late Glacial ◽  
Regional Variability ◽  
Local Conditions ◽  
Lithic Assemblages ◽  
Lithic Reduction ◽  
Organization Of Technology ◽  
Controlled Fracture ◽  
Technological Study

Abstract Miniaturized stone tools made by controlled fracture are reported from nearly every continent where archaeologists have systematically looked for them. While similarities in technology are acknowledged between regions, few detailed inter-regional comparative studies have been conducted. Our paper addresses this gap, presenting results of a comparative lithic technological study between Klipfonteinrand and Sehonghong – two large rock shelters in southern Africa. Both sites contain Late Glacial (~18-11 kcal BP) lithic assemblages, though they are located in regions with different geologies, climates and environments. Results demonstrate that lithic miniaturization manifests differently in these different regions. Both assemblages provide evidence for small blade production, though key differences exist in terms of the specific technological composition of this evidence, the raw materials selected, the role played by bipolar reduction and the manner in which lithic reduction was organized. Patterned variability of this nature demonstrates that humans deployed miniaturized technologies strategically in relation to local conditions.

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