Numerical analysis of mixed mode I and Mode II fracture propagation

The friction coefficient, tip curvature, and different-width crack state influence the stress intensity factor (SIF). The maximum circumferential tensile stress (MTS) and minimum strain energy density criterion (S) face challenges in explaining the mode-II fracture propagation of cracks. The maximum radial shear stress (MSS) and modified twin shear stress factor (ITS) criteria are proposed as the brittle mode-II fracture criteria. The experiments and numerical analysis are also performed. The results indicate that the fracture angles of the MSS and ITS were similar and different from the results of MTS and S. The equivalent stress intensity factors (ESIFs) from the mixed mode I-II are proposed to determine the fracture mode. There are different fracture models for different cracks under tensile and compressive stresses. The ratio of the tensile strength to uniaxial compressive strength influenced the fracture angle of ITS. The lateral pressure coefficient (k) had a significant effect on the mode-II fracture angle when the angle between the crack and the vertical direction is less than 40° and the lateral pressure coefficient is more than 0. Because the same fracture mode k (k > 0) can inhibit mode-I fracturing, conversely, it can also promote mode-I fracturing. Experimental results and numerical simulations of fracture propagation under uniaxial compression confirmed that the theoretical results were correct.

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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.

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Pure mode I and pure mode II fracture resistance of modified hot mix asphalt at low and intermediate temperatures

Fatigue & Fracture of Engineering Materials & Structures ◽

10.1111/ffe.13508 ◽

2021 ◽

Author(s):

Mohammad Zarei ◽

Ali Abdi Kordani ◽

Mohsen Zahedi

Keyword(s):

Fracture Resistance ◽

Hot Mix Asphalt ◽

Mode I ◽

Mode Ii ◽

Pure Mode ◽

Mode Ii Fracture

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Mixed-Mode Interlaminar Fracture Toughness of Glass and Carbon Fibre Powder Epoxy Composites—For Design of Wind and Tidal Turbine Blades

Materials ◽

10.3390/ma14092103 ◽

2021 ◽

Vol 14 (9) ◽

pp. 2103

Author(s):

Christophe Floreani ◽

Colin Robert ◽

Parvez Alam ◽

Peter Davies ◽

Conchúr M. Ó. Brádaigh

Keyword(s):

Fracture Toughness ◽

Carbon Fibre ◽

Composite Structures ◽

Mixed Mode ◽

Epoxy Composites ◽

Mode I ◽

Mode Ii ◽

Pure Mode ◽

Interlaminar Fracture Toughness ◽

Interlaminar Fracture

Powder epoxy composites have several advantages for the processing of large composite structures, including low exotherm, viscosity and material cost, as well as the ability to carry out separate melting and curing operations. This work studies the mode I and mixed-mode toughness, as well as the in-plane mechanical properties of unidirectional stitched glass and carbon fibre reinforced powder epoxy composites. The interlaminar fracture toughness is studied in pure mode I by performing Double Cantilever Beam tests and at 25% mode II, 50% mode II and 75% mode II by performing Mixed Mode Bending testing according to the ASTM D5528-13 test standard. The tensile and compressive properties are comparable to that of standard epoxy composites but both the mode I and mixed-mode toughness are shown to be significantly higher than that of other epoxy composites, even when comparing to toughened epoxies. The mixed-mode critical strain energy release rate as a function of the delamination mode ratio is also provided. This paper highlights the potential for powder epoxy composites in the manufacturing of structures where there is a risk of delamination.

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