Variation Of Fracture Properties Research Articles

Fracture toughness in additive manufacturing by selective laser sintering: an overview

This paper presents manufacturing, testing, and computing steps for determining the fracture toughness property of polyamide PA 2200 processed by laser sintering using different process parameters. The design of the samples was conducted according to ASTM D5045-99 and ASTM D5528-01, and the fracture tests consist of four-point bending in symmetric and asymmetric configuration and double cantilever beam test. The process parameters selected as variables were in-plane orientation, spatial orientation, energy density of the process, and induced structural defects. The results provide an extended view regarding the variation of fracture properties when the manufacturing conditions in laser sintering are changed.

Application of Elastic-Plastic Fracture Mechanics to Determine the Locational Variation in Fracture Properties of Cortical Bone

Abstract The complex nature of bone material results in a locational variation of fracture and mechanical properties. The heterogeneity associated with bone material and complex hierarchical assembly results in several toughening mechanisms, such as plasticity, micro-cracking, viscoplasticity, etc. These toughening mechanisms and presence of water in bone material makes the linear elastic fracture mechanics (LEFM) inapplicable in such materials. The present work is focused on the elastic-plastic fracture mechanics (EPFM) approach to estimate the locational variation in fracture properties of buffalo cortical bone for longitudinal, as well as transverse orientation of cracking. Samples from upper, middle, and lower locations of bone diaphysis were tested using compact tension and single-edge notch-bending testing methods for longitudinal and transverse orientation of cracking, respectively. The crack-tip opening displacement (CTOD) approach was applied to determine fracture properties, such as CTOD toughness (δc), J integral (Jcδ), and equivalent fracture toughness (Kδc) at different locations of bone diaphysis. The effect of orientation and location on mechanical properties of cortical bone, such as elastic modulus (E) and yield strength (σys), was also analyzed with the help of tensile testing. The equivalent fracture toughness values (Kδc) obtained in the present work were found to be three times higher than the corresponding values reported in the previous reports where the LEFM approach was applied favoring the application of EPFM for bone materials. The mechanical properties, as well as the fracture properties, were found to be maximum at middle location and minimum at lower location of bone diaphysis. The locational variation in fracture and mechanical properties observed in the present work are considered to be because of locational distribution of collagen fibrils, minerals, porosity, and density at different locations of bone diaphysis.

Characterization of fractures and faults: a multi‐component passive microseismic study from the Ekofisk reservoir

ABSTRACTFractures and faults within a reservoir can provide important pathways for the movement of reservoir fluids. Understanding the character and properties of these features on a range of length scales can be vital for the efficient exploitation of natural resources, whether it be enhanced oil and gas recovery, the safe storage of CO2, or better exploitation of geothermal heat. The monitoring of microseismicity within a reservoir illuminates active faults, but these events can be also used to characterize fracture networks through measurements of seismic anisotropy. In this study we use microseismic data acquired over an 18‐day period in April 1997 at the Ekofisk oil field in the North Sea. Using the analysis of seismic multiplets we delineate a number of sub‐vertical tectonic faults, which are consistent with previous core data analysis and seismic reflection work. We use shear wave splitting measurements, which are indicative of fracture‐induced seismic anisotropy, to infer the orientation of aligned aseismic fracture sets within the reservoir. The estimated fracture dip and strike from the shear wave splitting analysis are consistent with the active tectonic fractures characterized by the multiplets, but this analysis also illuminates spatial variations in fracture properties. Such monitoring on a longer term and with multiple wells is a promising tool for better understanding fracture and fault‐controlled flow within reservoirs.

Effect of Microstructure on the Fracture Properties of UO2-5wt%CeO2 Pellets

The variation of fracture properties [toughness(KIC), strength(σf)] was mearsured for UO2-5wt%CeO2 pellets with different microstructures made by the use of different dopants(Li2O, Al2O3 and Cr2O3). The critical temperature difference(ΔTc), an important parameter of material behavior against thermal shock, was also studied by measuring the fracture strength as a function of the quenching temperature. Fracture toughness was not significantly varied, about 0.8Mpa.m1/2, despite the variation of grain size, while the fracture strength was varied from 40 to about 60 MPa with the grain size. The ΔTc in a Li2O doped UO2-5wt%CeO2 pellet decreased compared with that of the undoped UO2-5wt%CeO2 one, whereas that for Al2O3-doped or Cr2O3-doped UO2-5wt%CeO2 pellets increased to a less extent, irrespective of grain size. The variation in ΔTc is discussed in terms of the effect of different dopants.

Acid Penetration in Natural Fracture Networks

Summary In this paper we present a methodology for predicting the propagation of acid along natural fracture networks and the resulting etching of the fracture walls. The natural fracture network is modeled as a system of intersecting fractures that form a main pathway for acid transport and dissolution. The tails of the intersected fractures increase the leakoff from the main pathway and are accounted for in the model. The fracture-network-acidizing model is supported by comparisons with laboratory experiments and smaller-scale simulations that determined the nature of acid channeling at fracture intersections. Model results illustrate the effects variations in fracture properties have on acid propagation. The model predicts deeper acid penetration under matrix conditions than would be possible with matrix flow only.

Lifetime prediction of brittle materials having spatial variations in fracture properties K IC and v versus K 1

The lifetimes of brittle materials under conditions of subcritical crack growth are analysed to indicate the effects of spatial variations of KIC and v versus KI and methods for studying the variations are suggested.