scholarly journals Obtaining a Relationship Between Process Parameters and Fracture Characteristics for Hybrid CO2 Laser∕Waterjet Machining of Ceramics

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Dinesh Kalyanasundaram ◽  
Pranav Shrotriya ◽  
Pal Molian
Keyword(s):  
Crack Length ◽  
Energy Release ◽  
Co2 Laser ◽  
Process Parameters ◽  
Fracture Behavior ◽  
Local Heating ◽  
Stress Fields ◽  
Empirical Parameter ◽  
Equilibrium Crack ◽  
Machining Of Ceramics

A combined experimental and analytical approach is undertaken to identify the relationship between process parameters and fracture behavior in the cutting of a 1mm thick alumina samples by a hybrid CO2 laser∕waterjet (LWJ) manufacturing process. In LWJ machining, a 200W power laser was used for local heating followed by waterjet quenching of the sample surface leading to thermal shock fracture in the heated zone. Experimental results indicate three characteristic fracture responses: scribing, controlled separation, and uncontrolled fracture. A Green’s function based approach is used to develop an analytical solution for temperatures and stress fields generated in the workpiece during laser heating and subsequent waterjet quenching along the machining path. Temperature distribution was experimentally measured using thermocouples and compared with analytical predictions in order to validate the model assumptions. Computed thermal stress fields are utilized to determine the stress intensity factor and energy release rate for different configurations of cracks that caused scribing or separation of the workpiece. Calculated crack driving forces are compared with fracture toughness and critical energy release rates to predict the equilibrium crack length for scribed samples and the process parameters associated with transition from scribing to separation. Both of these predictions are in good agreement with experimental observations. An empirical parameter is developed to identify the transition from controlled separation to uncontrolled cracking because the equilibrium crack length based analysis is unable to predict this transition. Finally, the analytical model and empirical parameter are utilized to create a map that relates the process parameters to the fracture behavior of alumina samples.

Calculating Energy Release Rate as a Function of Crack Length Using a Multiple-Step Crack Closure Technique in Tire Finite Element Models

2018 ◽  
Vol 46 (3) ◽  
pp. 130-152
Author(s):  
Dennis S. Kelliher
Keyword(s):  
Finite Element ◽  
Energy Release Rate ◽  
Crack Length ◽  
Energy Release ◽  
Crack Closure ◽  
Release Rate ◽  
Fatigue Behavior ◽  
Three Dimensions ◽  
Quantitative Prediction ◽  
Closure Technique

ABSTRACT When performing predictive durability analyses on tires using finite element methods, it is generally recognized that energy release rate (ERR) is the best measure by which to characterize the fatigue behavior of rubber. By addressing actual cracks in a simulation geometry, ERR provides a more appropriate durability criterion than the strain energy density (SED) of geometries without cracks. If determined as a function of crack length and loading history, and augmented with material crack growth properties, ERR allows for a quantitative prediction of fatigue life. Complications arise, however, from extra steps required to implement the calculation of ERR within the analysis process. This article presents an overview and some details of a method to perform such analyses. The method involves a preprocessing step that automates the creation of a ribbon crack within an axisymmetric-geometry finite element model at a predetermined location. After inflating and expanding to three dimensions to fully load the tire against a surface, full ribbon sections of the crack are then incrementally closed through multiple solution steps, finally achieving complete closure. A postprocessing step is developed to determine ERR as a function of crack length from this enforced crack closure technique. This includes an innovative approach to calculating ERR as the crack length approaches zero.

Determination of Stress Intensity Factors for Gradient Stress Fields

1977 ◽  
Vol 99 (3) ◽  
pp. 477-484 ◽  
Author(s):  
J. M. Bloom ◽  
W. A. Van Der Sluys
Keyword(s):  
Stress Intensity ◽  
Crack Length ◽  
Stress Intensity Factors ◽  
Maximum Stress ◽  
Nuclear Industry ◽  
Stress Fields ◽  
Polynomial Method ◽  
Intensity Factors ◽  
Asme Code ◽  
Linear Envelope

This paper evaluates eight different analytical procedures used in determining elastic stress intensity factors for gradient or nonlinear stress fields. From a fracture viewpoint, the main interest in this problem comes from the nuclear industry where the safety of the nuclear system is of concern. A fracture mechanics analysis is then required to demonstrate the vessel integrity under these postulated accident conditions. The geometry chosen for his study is that of a 10-in. thick flawed plate with nonuniform stress distribution through the thickness. Two loading conditions are evaluated, both nonlinear and both defined by polynomials. The assumed cracks are infinitely long surface defects. Eight methods are used to find the stress intensity factor: 1–maximum stress, 2–linear envelope, 3–linearization over the crack length from ASME Code, Section XI, 4–equivalent linear moment from ASME Code, Section III, Appendix G for thermal loadings, 5–integration method from WRC 175, Appendix 4 for thermal loadings, 6–8-node singularity (quarter-point) isoparametric element in conjunction with the displacement method, 7–polynomial method, and 8–semi-infinite edge crack linear distribution over crack. Comparisons are made between all eight procedures with the finding that the methods can be ranked in order of decreasing conservatism and ease of application as follows: 1–maximum stress, 2–linear envelope, 3–linearization over the crack length, 4–polynomial method, and 5–singularity element method. Good agreement is found between the last three of these methods. The remaining three methods produce nonconservative results.

A Study on the Lower Flanges Fracture of Endplate Bolted Connection

2006 ◽  
Vol 326-328 ◽  
pp. 983-986
Author(s):  
Hong Wei Ma ◽  
Chong Du Cho ◽  
Qiang Pan ◽  
Hyeon Gyu Beom
Keyword(s):  
Crack Length ◽  
High Stress ◽  
Transverse Load ◽  
Stress Fields ◽  
Finite Element Models ◽  
J Integral ◽  
Bolted Connection ◽  
Static Tests ◽  
Opening Mode ◽  
Set Up

The quasi-static tests on the endplate bolted connections of the new structure system consisting of SCC beam and CCSHRC column are briefly introduced in this paper. Meanwhile, the 3-D solid finite element models of the connections with pre-existing cracks in the lower flange’s high stress fields are set up by ANSYS. The material nonlinearities of concrete, steel and bars, together with the contact between the endplate and column surface are all considered in the model. With the transverse load applied on top of columns, the fracture parameters are calculated by APDL. The results indicate that the opening mode crack will happen mainly. When the pre-existing crack length is 2.50mm and the inter-storey drift is less than 6mm, the stress intensity factor values agree well with the converting values derived from J-integral and the crack tip fields are in elastic state. The J values are highly influenced by the pre-existing crack length, while seldom influenced by the concrete compression strength. Moreover, the J-integral have the trend to sharply increase when the pre-existing crack length is larger than 0.61mm, and the pre-existing crack will grow during loading when its length is larger than 1.35mm.

EXPERIMENTAL STUDY ON THE CO2 LASER CUTTING OF NOVEL POLYAMIDE 6/FLUOROELASTOMER THERMOPLASTIC ELASTOMERIC BLENDS

2015 ◽  
Vol 88 (1) ◽  
pp. 125-137 ◽  
Author(s):  
Shib Shankar Banerjee ◽  
Anil K. Bhowmick
Keyword(s):  
Low Power ◽  
Co2 Laser ◽  
Process Parameters ◽  
Laser Power ◽  
Laser Cutting ◽  
Manufacturing Industry ◽  
Cutting Speed ◽  
Polyamide 6 ◽  
Thermoplastic Elastomers ◽  
Dynamic Vulcanization

ABSTRACT The application of the low-power CO2 laser-cutting process to fluoroelastomer (FKM), polyamide 6 (PA6), PA6/FKM thermoplastic elastomers (TPEs), and their thermoplastic vulcanizate (TPV) is reported. The main laser process parameters studied were laser power, cutting speed, and material thickness. The value of the top and bottom widths of the slit that were formed during laser cutting (kerf width), melted transverse area, and melted volume per unit time were measured and analyzed. Interestingly, TPE showed a smaller melted area and melted volume per unit time when compared with those values with PA6. Dynamic vulcanization further decreased these values. For example, the melted areas of PA6 and TPE were 510 × 10−3 mm2 and 305 × 10−3 mm2, respectively, which reduced to 238 × 10−3 mm2 for TPV at 40 W laser power. FKM showed the lowest value (melted area of 180 × 10−3 mm2). In addition, the output quality of the cut surface was examined by measuring the root mean square (RMS) roughness of the cut edges and heat-affected zone (HAZ). The obtained results indicated that the dimension of the HAZ and RMS roughness largely decreased in TPE when compared with PA6. For example, the HAZ of PA6 was 700 μm, which decreased to 230 μm for TPE at 40 W laser power. On the other hand, HAZ was nonexistent for FKM. Infrared spectroscopic analysis showed that there was no structural change of TPE or pristine polymers after applying the low-power CO2 laser on the surface of materials. CO2 laser cutting will be a new technique in this industry, and this analysis will assist the manufacturing industry to choose a suitable laser system with exhaustive information of process parameters for cutting or machining of rubber, TPEs, and TPVs.

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.

Test Study of Fracture Mechanical Properties of Reactive Powder Concrete with Additives

2014 ◽  
Vol 904 ◽  
pp. 3-6 ◽  
Author(s):  
Zhi Gang Yin
Keyword(s):  
Mechanical Properties ◽  
Energy Release Rate ◽  
Fracture Energy ◽  
Energy Release ◽  
Release Rate ◽  
Fracture Behavior ◽  
Fracture Model ◽  
Reactive Powder Concrete ◽  
Critical Crack Length ◽  
Reactive Powder

The different influencing regular of fly-ash fractiontype of fibre (steel fibre and polypropylene fibre) and fibre fraction on the mechanical property and fracture behavior of Reactive Powder Concrete (PRC) are studied. Fracture mechanical properties of RPC is researched in double-K fracture model and fracture energy release rate G . Test results show that the crack propagation of RPC with steel fibers is limited. Its fracture toughness and pre-critical crack length is largely enhanced. Double-K fracture model and fracture energy release rate G are consistent with describing the fracture behavior of RPC.

Effect of CO2 laser cutting process parameters on edge quality and operating cost of AISI316L

2012 ◽  
Vol 44 (4) ◽  
pp. 1068-1082 ◽  
Author(s):  
H.A. Eltawahni ◽  
M. Hagino ◽  
K.Y. Benyounis ◽  
T. Inoue ◽  
A.G. Olabi
Keyword(s):  
Co2 Laser ◽  
Process Parameters ◽  
Laser Cutting ◽  
Operating Cost ◽  
Cutting Process ◽  
Edge Quality
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