Experimental and Numerical Investigation of Mixed-Mode Interlaminar Fracture of Carbon-Polyester Laminated Woven Composite by Using Arcan Set-up

Composite materials are widely used in marine, aerospace and automobile industries. These materials are often subjected to defects and damages from both in-service and manufacturing process. Delamination is the most important of these defects. This paper reports investigation of mixed-mode fracture toughness in carbon–polyester composite by using numerical and experimental methods. All tests were performed by Arcan set-up. By changing the loading angle, α, from 0° to 90° at 15° intervals, mode-I, mixed-mode and mode-II fracture data were obtained. Correction factors for various conditions were obtained by using ABAQUS software. Effects of the crack length and the loading angle on fracture were also studied. The interaction j-integral method was used to separate the mixed–mode stress intensity factors at the crack tip under different loading conditions. As the result, it can be seen that the shearing mode interlaminar fracture toughness is larger than the opening mode interlaminar fracture toughness. This means that interlaminar cracked specimen is tougher in shear loading condition and weaker in tensile loading condition.     

Rock fracture characterization using the modified Arcan test specimen

This study presents an application of fracture mechanics to determine mixed-mode fracture properties of rock using the numerical and experimental methods. The modified version of Arcan specimen test was, in association with a special loading device, an appropriate apparatus for experimental mixed-mode fracture analysis. Using the finite-element results, correction factors were applied to the specimens and a polynomial fit was proposed to evaluate the stress-intensity factors of a modified version of Arcan specimen with a crack subjected to mixed mode loading. The finite element analyses of specimens were also studied for various materials, different thickness and crack length. The mixed-mod fracture-toughness tests were carried out by using the modified Arcan test specimens over a wide range of loading angles. Using the finite element results, non-dimensional stress-intensity factors applied to the fracture specimen. By employing experimentally measured critical loads and the aid of the finite element method, mixed-mode fracture toughness for rock under consideration determined. The fracture surfaces under different mixed-mode loading conditions were examined by optical and scanning electron microscopy (SEM) to gain insight into the failure surfaces.     

Experimental investigation of mixed-mode fracture behaviour of woven laminated composite

In this paper, the mixed-mode interlaminar fracture behaviour of woven carbon-epoxy composite was investigated based on experimental and numerical analyses. A modified version of Arcan specimen was employed to conduct a mixed mode fracture test using a special loading device. A full range of mixed-mode loading conditions including pure mode-I and pure mode-II loading were created and tested. This test method has a simple procedure, clamping/unclamping the specimens are easy to achieve and only one type of specimen is required to generate all loading conditions. Also, finite element analysis was carried out for different loading conditions in order to determine correction factors needed for fracture toughness calculations. Interlaminar fracture toughness was determined experimentally with the modified version of the Arcan specimen under different mixed-mode loading conditions. Results indicated that the interlaminar cracked specimen is tougher in shear loading condition and weaker in tensile loading condition. Response of woven carbon-epoxy composite was also investigated through several criteria and the best criterion was selected. The interlaminar fracture surfaces of the carbon-epoxy composite under different mixed-mode loading conditions are examined by scanning electron microscopy (SEM).     

Mixed-mode cohesive fracture of adhesive joints: Experimental and numerical studies

A broad experimental and analytical effort using fracture mechanics as the prime tool was conducted to investigate and improve the understanding of the mixed-mode cohesive fracture behavior of bonded joints. As a part of experimental efforts, mixed-mode fracture tests were performed using modified Arcan specimens consisting of several combinations of adhesive, composite and metallic adherends with a special loading fixture, in which by varying the loading angle, from 0° to 90°, mode-I, mixed-mode and mode-II fracture data were obtained. Finite element analyses were also carried out on specimens with different adherends. The main objective of this study was to determine the fracture toughness K_IC and K_IIC for a range of substrates under mixed-mode loading conditions. Another goal was to study the relationship between the stress intensity factors and the fracture toughness. Based on those analyses, mixed mode fracture criterion for the adhesively bonded systems under consideration determined. Fracture surfaces obtained at different mixed-mode loading conditions for various adherends were finally discussed.     

Optimization of the Forward Osmosis Process Using Aquaporin Membranes in Chromium Removal

Due to the lack of affordable and feasible wastewater treatment technologies, various industries in developing countries are discharging chromium (Cr) without meeting the environmental standards. Here, the aim was to employ forward osmosis (FO) using aquaporins (AQP)-based biomimetic membranes and optimize the Cr rejection through response surface methodology (RSM). The initial concentration of draw solution, feed solution, and time was selected as independent variables in order to optimize Cr rejection and water flux. A high Cr rejection efficiency and water flux were achieved under the optimal conditions. These results revealed that the FO process applying an AQP membrane beside the RSM could be considered to treat wastewaters containing heavy metals.     

Effect of ingredient ratios of rigid polyurethane foam on foam core panels properties

One‐step manufacturing process (in‐situ foaming) provide great potential for the production of foam core panels. Polyurethane (PU) foam showed good applicability for use for in‐situ foaming. Here, the effect of ingredient ratios of rigid PU foam on foam performance and panel properties is investigated. It was observed that the isocyanate (ISO) content and polyols (PO) type and content significantly change the foam and panel properties. Foam cell density, as the most important factor influencing the foam characteristics, was higher in foams with higher ISO and polyether content. Bending strength, internal bond and screw withdrawal resistance of the foam core panels were significantly enhanced when the ISO and polyether content was increased in the foam formulation. Varying the ISO content had no influence on panel properties with higher content of polyester (60%) in the PO blend. Varying the foam ingredient ratios did not change the thickness swelling, while the water absorption was dependent on the foam components ratios. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44722.     

Experimental and numerical investigation of fracture of ABS polymeric material for different sample's thickness using a new loading device

The fracture behavior of ABS (acrylonitrile butadiene styrene) polymeric material has been investigated under the full range of in‐plane loading conditions using a new loading device to obtain more reliable results. Loading conditions from pure mode‐I through various mixed‐mode I/II ratios up to pure mode‐II have been generated using the proposed new loading device for the same specimen geometry. From the experimentally measured critical loads, the mode‐I, mode‐II, and the various mixed‐mode I/II critical energy release rates have been determined at different loading angles from 0° to 90°. Using the FE results, nondimensional stress intensity factors were applied to the specimen. The primary objectives of this study were to develop a new loading device to determine the mixed‐mode fracture toughness K_IC and K_IIC of ABS polymeric material. Another goal was to obtain stress intensity and strain energy release rates solutions associated with the crack, and to examine effects of thickness and geometric variables, particularly under mixed‐mode loading conditions. It was found that the thickness of the 10 mm specimen satisfied the plane strain condition with average fracture toughness ≈4.32 MPa·m^1/2 under pure mode‐I loading and ≈1.42 MPa·m^1/2 for pure mode‐II loading. POLYM. ENG. SCI., 54:2086–2096, 2014. © 2013 Society of Plastics Engineers     

On a Method of Paired Representation: Enhancement and Decomposition by Series Direction Images

In the paired representation, a two-dimensional (2-D) image is represented uniquely by a complete set of 1-D signals, so-called splitting-signals, that carry the spectral information of the image at frequency-points of specific subsets that divide the whole domain of frequencies. Image processing can thus be reduced to processing of splitting-signals and such process requires a modification of only a few spectral components of the image, for each signal. For instance, the α-rooting method of image enhancement can be fulfilled through processing one or a few splitting-signals. Such process can even be accomplished without computing the 2-D Fourier transforms of the original and enhanced images. To show that, we present an effective formula for inverse 2-D N×N-point paired transform, where N is a power of 2. The representation of the image and 2-D DFT by paired splitting-signals leads to the new concepts of direction and series images, that define the resolution and periodic structures of the image components, which can be packed in the form of the “resolution map” of the size of the image. Simple method of image enhancement by series images is described.

Characterization of fracture in adhesively bonded double-lap joints

A broad finite element study was carried out to understand the stress fields and stress intensity factors behavior of cracks in adhesively bonded double-lap joints, which are representative of loading in real aerospace structures. The interaction integral method and fundamental relationships in fracture mechanics were used to determine the mixed-mode stress intensity factors and associated strain energy release rates for various cases of interest. The numerical analyses of bonded joints were also studied for various kinds of adhesives and adherends materials, joint configurations, and thickness of adhesive and different crack lengths. The finite element results obtained show that the patch materials of low stiffness, low adhesive moduli and low tapering angles are desirable for a strong double-lap joint. In the double-lap joint, the shearing-mode stress intensity factor is always larger than that of the opening-mode and both shearing and opening mode stress intensity factors increase as the crack length increases, but their amplitudes are not sensitive to adhesive thickness. Results are discussed in terms of their relationship to adhesively bonded joints design and can be used in the development of approaches aimed at using adhesive bonding and extending the lives of adhesively bonded repairs for aerospace structures.