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1

An experimental investigation of fracture modes and delamination behaviour of carbon fiber reinforced laminated composite materials

Musafir Mustafa Abd Alhussein, Ameer Zuhair Jabbar Abdul, Hamzah Ahmed Fadhil

Diagnostyka

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2023

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Vol. 24, No. 1

art. no. 2023101

EN

Mechanically, composite laminates perform exceptionally well in-plane but poorly out-of-plane. Interlaminar damage, known as "delamination," is a major issue for composite laminates. Results from Mode-I and Mode-II experimental testing on twill-woven carbon fiber reinforced (CFRP) laminates are analyzed in this paper. Composite Mode-I fracture toughness was determined using three different methods in accordance with ASTM D5528: modified beam theory, compliance calibration, and a codified compliance calibration. Two methods, the Compliance Calibration Method and the Compliance-Based Beam Method, were used to determine the Mode-II fracture toughness in accordance with ASTM D7905. Stick-slip behavior is quite evident in the composite's ModeI fracture toughness test findings. The MBT technique's 𝐺Ic values for initiation and propagation are 0.533 and 0.679 KJ/m2 , respectively. When comparing the MBT approach to the industry-standard ASTM procedure for determining fracture toughness Mode-I, the MBT method was shown to be highly compatible. Furthermore, the 𝐺IIc values for the CBBM technique are 1.65 KJ/m2 for non-pre cracked and 1.4 KJ/m2 for pre-cracked materials. The CBBM method shows a good method to evaluate fracture toughness Mode-II, due to not needing to monitor the length of the crack during delamination growth to get the value of the fracture toughness.

2

Development and implementation of a testing method for the characterization of interlaminar delamination propagation in laminates under fatigue mode I loading conditions

Wilk J.

Prace Instytutu Lotnictwa

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2016

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Nr 4 (245)

239--250

EN

With no standardized methods for experimental characterization of fatigue delamination growth in laminates available the paper presents a testing method for mode I loading conditions. The distinctive feature of the proposed method is determination of crack length based on the specimen compliance and an additional compliance calibration procedure. This approach eliminates the need of visual observations. The testing methodology, using the double cantilever beam specimen, is described step by step as well as calculations leading to obtaining the relationship between the delamination growth rate and strain energy release rate values in the form of Paris' law The method was implemented in the Composites Testing Laboratory in the Institute of Aviation and the experimental investigations of crack resistance properties of laminates made of unidirectional prepreg MTM 46 were performed. Consistent results were obtained and the Paris law for I cracking mode was determined.

PL

W świetle braku dostępnych unormowanych metod zaprezentowano procedurę eksperymentalnego badania zmęczeniowego rozwoju delaminacji w warunkach I sposobu pękania. Wyróżniającą cechą zaproponowanego algorytmu jest wyznaczanie długości pęknięcia za pomocą podatności badanej próbki oraz dodatkowo przeprowadzanej kalibracji podatności. Zaprezentowane podejście pozwala wyeliminować konieczność obserwacji długości pęknięcia podczas testu. Opisana została krok po kroku metodologia, wykorzystująca próbkę w postaci podwójnej belki wspornikowej (Double Cantilever Beam), jak również przedstawione zostały obliczenia prowadzące do wyznaczenia zależności szybkości wzrostu delaminacji od wartości współczynnika uwalniania energii w postaci prawa Parisa. Metoda została wdrożona w Laboratorium Badań Kompozytów w Instytucie Lotnictwa. Przeprowadzono badania doświadczalne odporności na pękanie laminatu wykonanego z jednokierunkowego preimpregnatu MTM 46. Uzyskano zgodne wyniki oraz wyznaczono prawo Parisa dla I sposobu pękania.

3

Mode I crack problems by coupled fractal finite element and meshfree method

Rao B. N., Rajesh K. N.

Computer Assisted Mechanics and Engineering Sciences

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2010

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Vol. 17, no. 2-3-4

113-135

EN

This paper presents a coupling technique for integrating the fractal finite element method (FFEM) with element-free Galerkin method (EFGM) for analyzing homogeneous, isotropic, and two-dimensional linear-elastic cracked structures subjected to Mode I loading condition. FFEM is adopted for discretization of domain close to the crack tip and EFGM is adopted in the rest of the domain. In the transition region interface elements are employed. The shape functions within interface elements which comprise both the element-free Galerkin and the finite element shape functions, satisfy the consistency condition thus ensuring convergence of the proposed coupled FFEM-EFGM. The proposed method combines the best features of FFEM and EFGM, in the sense that no structured mesh or special enriched basis functions are necessary and no post-processing (employing any path-independent integrals) is needed to determine fracture parameters such as stress-intensity factors (SIFs) and T-stress. The numerical results show that SIFs and T-stress obtained using the proposed method, are in excellent agreement with the reference solutions for the structural and crack geometries considered in the present study. Also a parametric study is carried out to examine the effects of the integration order, the similarity ratio, the number of transformation terms, and the crack-length to width ratio, on the quality of the numerical solutions.