Configurational stability of a crack propagating in a material with mode-dependent fracture energy - Part I: Mixed-mode I+III

ASTM test standards for CMC’s Crack Growth Resistance (CGR) may exhibit a zig-zag (wavy) crack path pattern, and fiber bridging. The experimental parameters that may contribute to the difficulty can be summarized as: specimen width and thickness, interface coating thickness, mixed mode failure evolution, and interlaminar defects. Modes I crack growth resistances, GI were analytically determined at ambient temperature using wedge test, a modified double cantilever beam (DCB). Several Finite Element (FE) based Multi-scale modeling potential techniques were investigated: a) Multi-scale progressive failure analysis (MS-PFA); b) Virtual Crack Closure Technique (VCCT). Advantages and disadvantages of each were identified. The final modeling algorithm recommended was an integrated damage and fracture evolution methodology using combined MS-PFA and VCCT. The material tested in this study was a slurry-cast melt-infiltrated SiC/SiC composite with Tyranno ZMI fibers (Ube Industries, Kyoto, Japan) and a BN interphase. The fiber architecture consisted of eight plies of balanced 2-D woven five-harness satin. The total fiber volume fraction was about 30% with half of the fibers in the 0° direction and half in the 90° direction. All specimens had a nominal thickness of 4 mm. An alumina wedge with 18° head angle (2α) was used. In this method, a splitting force is created by inserting a vertically-moving wedge in a notch causing the arms to separate and forcing an interlaminar crack at the sharpest end of the notch The MS-PFA numerical model predicted the damage and fracture evolution and utilized the GENOA UMAT (User Material Subroutine) for Damage and FEM (Finite Element Model) stress intensity and LEFM (Linear elastic Fracture Model), Cohesive Model for Fracture. The analysis results (Fracture energy vs. crack length, Fracture energy vs. load, Fracture energy vs. crack opening displacement) matched the Mode I coupon tests and revealed the following key findings. Mode I-Wedge specimen exhibits: 1) failure mode is due to interlaminar tension (ILT) only in the interface section and a zig-zag pattern observed; 2) VCCT crack growth resistance is well matched to the test data; and 3) failure mode is a mixed mode behavior of Interlaminar tension (ILT) to interlaminar shear (ILS). The final Wedge test specimen configuration optimization includes the sensitivity of design parameters to CGR: a) wedge contact coefficient of friction; b) lever arms thickness, and c) inclined head angle, distance between the initial crack and wedge tip.

Download Full-text

Mixed mode (I/II) fracture energy of cement emulsified asphalt mortar under intermediate temperature

Engineering Fracture Mechanics ◽

10.1016/j.engfracmech.2020.107374 ◽

2021 ◽

Vol 241 ◽

pp. 107374

Author(s):

Shima Najjar ◽

Abolfazl Mohammadzadeh Moghaddam ◽

Ali Sahaf

Keyword(s):

Fracture Energy ◽

Mixed Mode ◽

Intermediate Temperature ◽

Mode I ◽

Emulsified Asphalt ◽

Asphalt Mortar

Download Full-text

Mixed-Mode Fracture Characteristics of Cold Recycling Mixes with Emulsified Asphalt

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.204-208.1678 ◽

2012 ◽

Vol 204-208 ◽

pp. 1678-1683 ◽

Cited By ~ 1

Author(s):

Lei Gao ◽

Fu Jian Ni ◽

Mei Kun Yang

Keyword(s):

Fracture Energy ◽

Mixed Mode ◽

Peak Load ◽

Mode I ◽

Mixed Mode Fracture ◽

Fracture Characteristics ◽

Loading Rates ◽

Crack Angle ◽

Cold Recycling ◽

Emulsified Asphalt

In order to study the Mixed-Mode cracking behavior of cold recycling mixes with emulsified asphalt, the Arcan test configuration was chosen to perform the fracture characteristics of cold recycling mixes in five levels of Mixed-Mode (100, 75, 50, 25 and 0% Mode I) at three loading rates (1.0mm/min, 0.5mm/min, 0.1mm/min). The load and load-line displacement, peak load, crack angle and fracture energy were all used for further analysis. The process of cracking can be divided into three stages: the stage of crack arises, expand stage, and the brittle break stage; 0% Mode I has a significant difference from the others; the loading rates and levels of Mixed-Mode both have great influence on peak load; the higher level of Mode I usually gets lower crack angle; the fracture energy of 100% Mode I ranges from 168 J/m2 to 308 J/m2 and the specimen in 0.5mm/min has greater fracture energy.

Download Full-text

Mixed mode fracture testing of adhesively bonded wood specimens using a dual actuator load frame

Holzforschung ◽

10.1515/hf.2010.041 ◽

2010 ◽

Vol 64 (3) ◽

Cited By ~ 15

Author(s):

Hitendra K. Singh ◽

Abhijit Chakraborty ◽

Charles E. Frazier ◽

David A. Dillard

Keyword(s):

Fracture Energy ◽

Mixed Mode ◽

Mode I ◽

Mode Ii ◽

Mixed Mode Fracture ◽

Pure Mode ◽

Mixed Mode Loading ◽

Mode Mixity ◽

Adhesively Bonded ◽

Phase Angles

Abstract An experimental evaluation of mixed mode fracture tests conducted on adhesively bonded wood specimens using a dual actuator load frame is presented. This unit allows the fracture mode mixity to be easily varied during testing of a given specimen, providing improved consistency, accuracy, and ease of testing over a range of loading modes. Double cantilever beam (DCB) type specimens made of southern yellow pine (Pinus spp.) wood substrates bonded with a commercially available one part polyurethane adhesive were tested over a wide range of mode mixities from pure mode I to pure mode II. The critical strain energy release rate (SERR) values were calculated from the measured load, displacement, and crack length data, in combination with material properties and specimen geometric parameters, and compared on a versus fracture envelope plot. Mean quasi-static fracture energy values were calculated to be 390 J m-2 and 420 J m-2 for mode I and mode II fracture, respectively. For various mixed mode phase angles, the critical SERR values were partitioned into mode I and mode II components. In mixed mode loading conditions the cracks were typically driven along the interface, which resulted in lower total fracture energy values when compared with those measured under pure mode I loading conditions. A drop in measured fracture energy of approximately 45% was observed with mode mixity phase angles as small as 16°, implying that engineering designs based on results from the popular mode I DCB test could be nonconservative in some situations. Fracture surfaces obtained at different mode mixities are also discussed. An improved understanding of fracture behavior of adhesively bonded wood joints under mixed mode loading through generation of fracture envelopes could lead to improved designs of bonded wood structures.

Download Full-text

Ceramic Matrix Composite Interlaminar Fracture Toughness (Mode I-II) Characterization

Volume 6: Ceramics; Controls, Diagnostics and Instrumentation; Education; Manufacturing Materials and Metallurgy; Honors and Awards ◽

10.1115/gt2015-44047 ◽

2015 ◽

Author(s):

Frank Abdi ◽

Harsh Baid ◽

Jalees Ahmad ◽

Steve Gonczy ◽

Gregory N. Morscher ◽

...

Keyword(s):

Fracture Toughness ◽

Fracture Energy ◽

Mixed Mode ◽

Test Methods ◽

Mode I ◽

Mode Ii ◽

Mode Ii Fracture ◽

Test Standards ◽

Mode Behavior ◽

Mode Ii Fracture Toughness

The objective of this effort is to develop and demonstrate innovative interlaminar Mode I and Mode II fracture toughness analysis and test methods for ceramic matrix composites (CMC). Currently, there are number of American Society for Testing and Materials (ASTM) test standards for CMC’s at both ambient and elevated temperatures, including interlaminar tension and shear strength test methods. However, there are no standardized test methods for determination of interlaminar fracture toughness in CMC’s. Although research work exists on interlaminar Mode I and Mode II fracture toughness of various types of CMC’s, the test methods applied particularly in Mode II fracture toughness testing showed definite drawbacks and limitations. ASTM test standards for CMC’s may exhibit a zig-zag (wavy) crack path pattern, and fiber bridging. The experimental parameters that may contribute to the difficulty can be summarized as: specimen width and thickness, interface coating thickness, mixed mode failure evolution, and interlaminar defects. Modes I and II crack growth resistances, GI and GII, were analytically determined at ambient temperature using double cantilever beam (DCB) and End Notched Flexure (ENF) geometries. Three (3) CMC material systems were analyzed (Sylramic/IBN/MI, SiC/SiC CVI, and SiC/CAS). Several Finite Element (FE) based potential techniques were investigated: a) Multi-scale progressive failure analysis (MS-PFA); b) Virtual Crack Closure Technique (VCCT); and c) Contour Integral (CI). Advantages and disadvantages of each were identified. The final modeling algorithm recommended was an integrated damage and fracture evolution methodology using MS-PFA and VCCT. The analysis results (Fracture energy vs. crack length, Fracture energy vs. load, Fracture energy vs. crack opening displacement) matched the Mode I and Mode II coupon tests and revealed the following key findings. Mode I-DCB specimen: 1) Sylramic/IBN/MI failure mode is due to interlaminar tension (ILT) only in the interface section and a zig-zag pattern observed 2) VCCT crack growth resistance of Sylramic/IBN/MI is well matched to the test data and 3) SiC/SiC CVI failure mode is a mixed mode behavior (ILT to interlaminar shear (ILS). Mode II ENF specimen MS-PFA analysis suggests mixed mode behavior and the zig-zag pattern similar to Mode I coupon tests.

Download Full-text