Fracture Properties of an Anisotropic Biological Cellular Material - Apple Flesh

1990 ◽  
Vol 207 ◽  
Author(s):  
Ali A. Khan ◽  
Julian F. V. Vincent
Keyword(s):  
Fracture Toughness ◽  
Marked Effect ◽  
Crack Opening ◽  
Cellular Material ◽  
Taste Panel ◽  
Slow Freezing ◽  
Intercellular Spaces ◽  
Fracture Properties ◽  
Parenchyma Cells ◽  
Fracture Tests

AbstractThe texture of apple flesh is important in assessing its eating qualities. The texture in turn is related to the structure of the parenchyma. The parenchyma cells of the fruit are arranged in radial quasi-columnar form with radial spaces in between. This anisotropy has a marked effect on the fracture properties such that it is much easier to drive a crack between the columns (radially) than to drive it across them (tangentially). The fracture tests used were simple crack-opening tests under tension or using a wedge. This difference was also detected by a taste panel. The radial spaces ease the passage of cracks travelling along them, and act as crack stoppers for cracks travelling at right angles to them. They also allow the cells to deform more in one orientation more giving the structure ductility and making the apple tougher in that orientation. It is possible to increase this effect by controlled damage such as slow freezing which causes the intercellular spaces to expand increasing the crack-stopping mechanisms and increasing the ductility, therefore increasing the fracture toughness. Toughness first increases, then decreases with increasing damage. This effect can be mimicked with brittle paper: fracture toughness of tracing paper initially increases if holes are punched randomly in it.

Fracture Toughness Determinations of A-302B and Ni-Mo-V Steels With Various Size Specimens

1966 ◽  
Vol 88 (4) ◽  
pp. 783-791 ◽  
Author(s):  
D. F. Mowbray ◽  
A. J. Brothers ◽  
S. Yukawa
Keyword(s):  
Fracture Toughness ◽  
Crack Opening ◽  
Bend Angle ◽  
Opening Displacement ◽  
Fatigue Precrack ◽  
Strain Fracture ◽  
Shear Lip ◽  
Angle Crack ◽  
Fracture Tests ◽  
Increasing Temperature

Fracture tests were conducted on three steels obtained from heavy-section pieces over a range of test temperatures using single-edge notched (SEN) specimens under tensile loading and notched-bar (NB) specimens in bending. The SEN tests were performed on specimens 0.125 and 0.4 in. thick plus a few specimens 0.020 in. thick. In the NB series Charpy-sized specimens (0.4 in. square) were tested at various temperatures with additional tests on smaller and larger specimens up to 6 in. square at selected temperatures. All specimens were provided with a fatigue precrack at the tip of the notch. The tests were conducted to determine the capability of various size specimens for providing valid plane-strain fracture toughness (GIc or KIc) values at various temperatures for these steels. At very low temperatures all specimens gave similar KIc values. With increasing temperature, KIc values obtained from the larger specimens remained relatively constant and then increased rapidly. At higher temperatures within this range, valid KIc values could not be measured with small specimens. Two possible methods of estimating KIc at these temperatures from small specimen data are discussed. One of these involves a correlation between fracture toughness and shear-lip thickness. The second makes use of a relation between bend angle, crack-opening-displacement, and fracture toughness. The test results are analyzed to show that both methods can be very useful.

scholarly journals Creep and fracture of warm columnar freshwater ice

2021 ◽  
Vol 15 (5) ◽  
pp. 2401-2413
Author(s):  
Iman E. Gharamti ◽  
John P. Dempsey ◽  
Arttu Polojärvi ◽  
Jukka Tuhkuri
Keyword(s):  
Constitutive Model ◽  
Crack Opening ◽  
Optimization Procedure ◽  
Rectangular Plates ◽  
Test Results ◽  
Fracture Properties ◽  
Columnar Grains ◽  
Growth Initiation ◽  
Fracture Tests ◽  
Creep Loading

Abstract. This work addresses the time-dependent response of 3 m×6 m floating edge-cracked rectangular plates of columnar freshwater S2 ice by conducting load control (LC) mode I fracture tests in the Aalto Ice Tank of Aalto University. The thickness of the ice plates was about 0.4 m and the temperature at the top surface about −0.3 ∘C. The loading was applied in the direction normal to the columnar grains and consisted of creep/cyclic-recovery sequences followed by a monotonic ramp to fracture. The LC test results were compared with previous monotonically loaded displacement control (DC) experiments of the same ice, and the effect of creep and cyclic sequences on the fracture properties were discussed. To characterize the nonlinear displacement–load relation, Schapery's constitutive model of nonlinear thermodynamics was applied to analyze the experimental data. A numerical optimization procedure using Nelder–Mead's (N-M) method was implemented to evaluate the model functions by matching the displacement record generated by the model and measured by the experiment. The accuracy of the constitutive model is checked and validated against the experimental response at the crack mouth. Under the testing conditions, the creep phases were dominated by a steady phase, and the ice response was overall elastic–viscoplastic; no significant viscoelasticity or major recovery was detected. In addition, there was no clear effect of the creep loading on the fracture properties at crack growth initiation: the failure load and crack opening displacements.

scholarly journals Toughness Calculation of Postfire Normal Concrete

2014 ◽  
Vol 2014 ◽  
pp. 1-8
Author(s):  
Qingyang Chen ◽  
Anjing Tang ◽  
Zhoudao Lu
Keyword(s):  
Fracture Toughness ◽  
Critical Load ◽  
Crack Opening Displacement ◽  
Analytical Method ◽  
Crack Opening ◽  
Fracture Model ◽  
Opening Displacement ◽  
Normal Concrete ◽  
Critical Fracture ◽  
Fracture Tests

Fracture tests of postfire normal concrete with ten temperatures up to 600°C are implemented. Residual fracture toughness using analytical method is determined. Two situations are divided at critical load when calculating the cohesive fracture toughness. The initial and critical fracture toughness could be calculated from the complete load-crack opening displacement curves. Finally, the validation of double-Kfracture model to the postfire concrete specimens is proved.

Fracture Tests Of Polysilicon Film

1997 ◽  
Vol 505 ◽  
Author(s):  
W. N. Sharpe ◽  
B. Yuan ◽  
R. L. Edwards
Keyword(s):  
Thin Films ◽  
Fracture Toughness ◽  
Crack Opening Displacement ◽  
Crack Opening ◽  
Tensile Loading ◽  
Opening Displacement ◽  
Polysilicon Film ◽  
Fracture Tests

ABSTRACTA new test approach is presented to measure the fracture toughness of thin films. The polysilicon specimen is a center-cracked panel that is 3.5 μm thick and 3 mm wide with a 100 μm long slot in the center. It is subjected to tensile loading, and the crack-opening displacement is measured by interferometry. The average toughness is 1.4 ± 0.65 MPa-m1/2.

scholarly journals Elastic-viscoplastic characterization of S2 columnar freshwater ice

2020 ◽  
Author(s):  
Iman E. Gharamti ◽  
John P. Dempsey ◽  
Arttu Polojärvi ◽  
Jukka Tuhkuri
Keyword(s):  
Constitutive Model ◽  
Crack Opening ◽  
Optimization Procedure ◽  
Rectangular Plates ◽  
Test Results ◽  
Fracture Properties ◽  
Apparent Fracture Toughness ◽  
Fracture Tests ◽  
Creep Loading

Abstract. This work addresses the time-dependent response of 3 m × 6 m floating edge-cracked rectangular plates of columnar freshwater S2 ice by conducting load control (LC) mode I fracture tests at −2 °C in the Ice Tank of Aalto University. The loading profile consisted of creep/cyclic-recovery sequences followed by a monotonic ramp to fracture. The LC test results were compared with previous monotonically loaded displacement control (DC) experiments of the same ice, and the effect of creep and cyclic sequences on the fracture properties were discussed. To characterize the nonlinear displacement-load relation, Schapery's constitutive model of nonlinear thermodynamics was applied to analyze the experimental data. A numerical optimization procedure using Nelder-Mead's (N-M) method was implemented to evaluate the model functions by matching the displacement record generated by the model and measured by the experiment. The accuracy of the constitutive model is checked and validated against the experimental response at the crack mouth. Under the testing conditions, the creep phases were dominated by a steady phase, and the ice response was elastic-viscoplastic; no viscoelasticity or major recovery were detected. In addition, there was no clear effect of the creep loading on the fracture properties: the apparent fracture toughness, failure load, and crack opening displacements.

Evaluation of Wedge Splitting Fracture Tests Using the Double-K Model: Analysis of the Effect of Hemp Fibre Dosage and Length in Concrete Specimens

2016 ◽  
Vol 249 ◽  
pp. 142-146
Author(s):  
Hana Šimonová ◽  
Ivana Havlíková ◽  
Jakub Sobek ◽  
Alaa Abdulrahman ◽  
Zbyněk Keršner ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Crack Propagation ◽  
Crack Opening Displacement ◽  
Crack Opening ◽  
Opening Displacement ◽  
Critical Crack ◽  
Hemp Fibre ◽  
Fracture Tests ◽  
Critical Crack Opening ◽  
Wedge Splitting

This paper deals with the results obtained from the employment of a selected fracture model to evaluate wedge splitting fracture tests carried out on hemp fibre concrete specimens. The research work was focused mainly on the effect of the dosage and length of hemp fibres on the initiation part of crack propagation in concrete specimens, and on critical crack opening displacement. Concrete mixtures with different volumetric dosages (0.5, 1.0 and 2.0 %) and fibre lengths (10, 20 and 40 mm) were prepared, and six identical specimens were cast from each mixture. Specimens were also cast from a reference mixture, which was without fibres. The specimens were provided with an initial notch and tested using the wedge splitting test method. Load versus crack mouth opening displacement diagrams were recorded during testing and (after data filtering and appropriate modifications) subsequently evaluated using the Double-K fracture model. This model allows the evaluation of two material parameters – the initiation fracture toughness, which defines the onset of stable crack propagation, and the unstable fracture toughness, which defines the onset of unstable cracking or failure. Finally, the critical crack opening displacement was determined with the assumption of the bilinear function of softening in tension.

The Fracture Toughness of Hardened Tool Steels

1987 ◽  
Vol 109 (4) ◽  
pp. 314-318 ◽  
Author(s):  
D. F. Watt ◽  
Pamela Nadin ◽  
S. B. Biner
Keyword(s):  
Fracture Toughness ◽  
Crack Growth ◽  
Slow Crack Growth ◽  
Crack Opening ◽  
Compact Tension ◽  
Testing Procedure ◽  
Tool Steels ◽  
Opening Displacement ◽  
Tempering Temperature ◽  
Toughness Testing

This report details the development of a three-stage fracture toughness testing procedure used to study the effect of tempering temperature on toughness in 01 tool steel. Modified compact tension specimens were used in which the fatigue precracking stage in the ASTM E-399 Procedure was replaced by stable precracking, followed by a slow crack growth. The specimen geometry has been designed to provide a region where slow crack growth can be achieved in brittle materials. Three parameters, load, crack opening displacement, and time have been monitored during the testing procedure and a combination of heat tinting and a compliance equation have been used to identify the position of the crack front. Significant KIC results have been obtained using a modified ASTM fracture toughness equation. An inverse relationship between KIC and hardness has been measured.

Finite Element Modeling of Microcrack Growth in Cortical Bone

2011 ◽  
Vol 78 (4) ◽  
Author(s):  
Susan Mischinski ◽  
Ani Ural
Keyword(s):  
Fracture Toughness ◽  
Finite Element ◽  
Elastic Modulus ◽  
Crack Growth ◽  
Line Strength ◽  
Crack Deflection ◽  
Cement Line ◽  
Fracture Properties ◽  
Cement Lines ◽  
Microcrack Growth

Bone is similar to fiber-reinforced composite materials made up of distinct phases such as osteons (fiber), interstitial bone (matrix), and cement lines (matrix-fiber interface). Microstructural features including osteons and cement lines are considered to play an important role in determining the crack growth behavior in cortical bone. The aim of this study is to elucidate possible mechanisms that affect crack penetration into osteons or deflection into cement lines using fracture mechanics-based finite element modeling. Cohesive finite element simulations were performed on two-dimensional models of a single osteon surrounded by a cement line interface and interstitial bone to determine whether the crack propagated into osteons or deflected into cement lines. The simulations investigated the effect of (i) crack orientation with respect to the loading, (ii) fracture toughness and strength of the cement line, (iii) crack length, and (iv) elastic modulus and fracture properties of the osteon with respect to the interstitial bone. The results of the finite element simulations showed that low cement line strength facilitated crack deflection irrespective of the fracture toughness of the cement line. However, low cement line fracture toughness did not guarantee crack deflection if the cement line had high strength. Long cracks required lower cement line strength and fracture toughness to be deflected into cement lines compared with short cracks. The orientation of the crack affected the crack growth trajectory. Changing the fracture properties of the osteon influenced the crack propagation path whereas varying the elastic modulus of the osteon had almost no effect on crack trajectory. The findings of this study present a computational mechanics approach for evaluating microscale fracture mechanisms in bone and provide additional insight into the role of bone microstructure in controlling the microcrack growth trajectory.

Fracture assessment of polycarbonate parts produced by fused deposition modeling in the out-of-plane printing direction – effect of raster angle

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Iman Sedighi ◽  
Majid R. Ayatollahi ◽  
Bahador Bahrami ◽  
Marco A. Pérez-Martínez ◽  
Andrés A. Garcia-Granada
Keyword(s):  
Fracture Toughness ◽  
Finite Element ◽  
Fracture Behavior ◽  
Fused Deposition Modeling ◽  
Mode I ◽  
Content Type ◽  
Fused Deposition ◽  
Out Of Plane ◽  
Deposition Modeling ◽  
Fracture Tests

Purpose The purpose of this paper is to study the Mode I fracture behavior of polycarbonate (PC) parts produced using fused deposition modeling (FDM). The focus of this study is on samples printed along the out-of-plane direction with different raster angles. Design/methodology/approach Tensile and Mode I fracture tests were conducted. Semi-circular bend specimens were used for the fracture tests, which were printed in four different raster patterns of (0/90), (15/−75) (30/−60) and (45/−45). Moreover, the finite element method (FEM) was used to determine the applicability of linear elastic fracture mechanics (LEFM) for the printed PC parts. The fracture toughness results, as well as the fracture path and the fracture surfaces, were studied to describe the fracture behavior of the samples. Findings Finite element results confirm that the use of LEFM is allowed for the tested PC samples. The fracture toughness results show that changing the direction of the printed rasters can have an effect of up to 50% on the fracture toughness of the printed parts, with the (+45/−45) and (0/90) orientations having the highest and lowest resistance to crack propagation, respectively. Moreover, except for the (0/90) orientation, the other samples have higher crack resistance compared to the bulk material. The fracture toughness of the tested PC depends more on the toughness of the printed sample, rather than its tensile strength. Originality/value The toughness and the energy absorption capability of the printed samples (with different raster patterns) were identified as the main properties affecting the fracture toughness of the AM PC parts. Because the fracture resistance of almost all the samples was higher than that of the base material, it is evident that by choosing the right raster patterns for 3D-printed parts, very high resistance to crack growth may be obtained. Also, using FEM and comparing the size of the plastic zones, it was concluded that, although the tensile curves show nonlinearity, LEFM is still applicable for the printed parts.

The Spherical Indentation Approach for Fracture Toughness Evaluation: A Study Based on the Energy Release Rate

2018 ◽  
Author(s):  
Tairui Zhang ◽  
Weiqiang Wang ◽  
Aiju Li
Keyword(s):  
Fracture Toughness ◽  
Energy Release Rate ◽  
Energy Release ◽  
Release Rate ◽  
Damage Mechanism ◽  
Tensile Tests ◽  
Uniaxial Tensile ◽  
Spherical Indentation ◽  
Material Damage ◽  
Fracture Tests

In this study, we investigated the drawbacks of previous studies regarding the evaluation of fracture toughness from spherical indentation tests (SITs). This was achieved by an examination of the material damage mechanism during indentation tests, uniaxial tensile tests, and Mode I/II fracture tests. A new approach based on the energy release rate was proposed in this study to evaluate the fracture toughness of ductile metals. Scanning electron microscope (SEM) observations revealed that the mechanism for material damage during an indentation test was different with the material damage in uniaxial tensile tests and Mode I fracture tests, but similar to that in Mode II fracture tests. Thus, the energy release rate during SITs should be correlated with JIIC. Compared with previous studies, this new proposed method was more consistent with the actual damage mechanism and did not rely on the specific critical damage values. Experiments on SA508, SA533, 15CrMoR, and S30408 revealed that the maximum error from this energy release rate-based approach was no more than 13% when compared with their conventional counterparts (compact tension tests), and thus can meet the precision requirement of engineering applications.

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