Sabit Adanur

Bending, compression, and shear behavior of woven glass fiber/epoxy composites

The mechanical properties and failure mechanisms of through-the-thickness stitched plain weave glass fabric‐epoxy composites were studied. Unstitched plain weave and biaxial non-crimp fabrics were used for comparison. Composite panels were fabricated using Resin Transfer Molding. Z-directional stitching increased the delamination resistance and lowered the bending strength of the composites. Composites made from through-the-thickness stitched fabrics demonstrated improved compression after impact behavior as compared to the unstitched fabrics. The results presented in this investigation should be useful in tailoring textile composites to achieve specific property goals. q 2000 Elsevier Science Ltd. All rights reserved.

Mechanical and thermo-mechanical failure mechanism analysis of fiber/filler reinforced phenolic matrix composites

Abstract Three groups of phenolic matrix composites were investigated in this study: (1) powder (glass, ceramic and carbon black) filled phenolic resin, (2) graphite fiber reinforced phenolic resin, and (3) graphite fiber/glass powder reinforced phenolic resin. In the first part of this study, the three-point bending test method was used to measure the mechanical properties of these composites. The graphite fiber/10 wt% glass powder filled phenolic composite exhibited higher flexural strength and flexural modulus than the unfilled graphite fiber reinforced phenolic resin composite. Samples were examined using an optical microscope and scanning electron microscope (SEM). The amount of wedge-shaped voids could be greatly reduced by introducing the glass powder to the phenolic resin. The filler acted to delay crack propagation by deflecting the crack such that it propagated along the interface of the carbon fiber and the matrix. In the second part of this study, the effects of temperature (up to 500°C) on the mechanical properties of graphite fiber reinforced phenolic (G/P) and graphite fiber/glass particle reinforced (G/g-P) composites were investigated. The results show that G/g-P composites exhibited higher flexural strength and flexural modulus than the G/P composites at exposure temperatures up to 360°C. The thermal stresses induced due to heating in the composite were analyzed by the Thick-Cylinder Model (TCM) and Selsings model. At temperatures above 300°C, tensile thermal stresses tended to promote the formation of micro-cracks at the fiber/matrix interface, which degraded the properties of G/P composites. Debonding between the glass particle and the matrix occurred at a temperature above 360°C, which greatly degraded the properties of G/ g-P composites.

3D modeling of textile composite preforms

The purpose of this paper is to present three-dimensional models of fabric reinforcements for composite components by using computer aided geometric design (CAGD) techniques. A novel approach to structural representation of fabric preforms is described in both parametric and graphic forms. The philosophy behind the development of the computer generated model of a composite fabric reinforcement is discussed. The model described here is a general one, capable of producing a 3D representation of any 2D and 3D fabrics. The computer program also provides a very useful visualisation of the structure. Various structures of fabrics used as reinforcements for composite materials, such as woven, braided, knit, and multi-axial 3D weave, are demonstrated in virtual realistic forms.

Fiber Arrangement Characteristics and Their Effects on Nonwoven Tensile Behavior

Our early model for predicting nonwoven fabric stress-strain behavior by the finite element method is generalized to include the effects of fiber curl, which is shown to have a great effect on the tensile behavior of the fabric. A numerical method to characterize the lateral contraction of nonwovens during tensile deformation is presented. The effects of fiber arrangement characteristics on the mechanical properties of nonwovens are studied through laboratory experiments and theoretical analysis. The effects of varying thick nesses within the nonwovens on fabric strength, modulus, and stress-strain distribution are also examined. Tensile testing of several nonwoven fabrics verifies the theoretical results.

A Novel Approach to Three-Dimensional Modeling of Interlaced Fabric Structures

This paper attempts the geometric modeling of woven and braided fabric structures in three dimensions using a computer aided geometric design (CAGD) technique. A new symbolic approach to fabric structure representation, which is useful to the textile CAD/CAM process and fabric design, is presented, and a basic model is proposed that treats a yarn as a three-dimensional solid object. Some traditional 2D fabric models are extended into 3D models and demonstrated in 3D form. The structures of various fabrics are demonstrated in graphic forms, including elementary weaves such as plain weave, twill, and satin; two layer fabrics; braided fabrics; and three-dimensional fabrics as reinforcements for composite materials.

Nanocomposite Fiber Based Web and Membrane Formation and Characterization

Electrospinning is used to produce polyvinyl alcohol (PVA) fibers. Electrospun nano and micro sized fibers are collected on nonwoven fabrics to form a web and membranes. Optimization is carried out by considering some of the parameters, such as voltage, spinning time, polymer solution, distance between the collector and the needle. Beading effect, effect of solution viscosity, and voltage are investigated. Mechanical and thermal properties are measured by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Surface tension properties are examined. Glass transition and melting temperature are increased with the addition of nanoclay to PVA. Nanoclay also increases the barrier properties and thermal stability of PVA fibers. Yarn samples are produced by twisting nano-micro fibers. Tensile strength of the yarn samples is measured.

Structural Analysis of a Two-dimensional Braided Fabric

Two-dimensional-braid geometry is analyzed. The cover factor of a fabric braided on a particular braider depends on three variables: braid angle, helical length, and braid diameter; however, only two of the three are independent because of an equation of constraint. The cover factor of an existing braid is a function of braid angle and diameter and maintains a constant helical length between its tensile and compressive jammed states. A stable jammed state with maximum crimp is found to exist when the braid angle is 45° and the helical length is a minimum. When the braid diameter is held constant by braiding on a constant-diameter mandrel, the cover factor is increased by decreasing the helical length or increasing the braid angle. The cover factor is directly related to the fabric width as a single independent variable. When the yarn cannot be considered as a flat strip but must instead be considered to have a circular cross-section, the maximum cover factor in the jammed state is shown to be 0.82.

PREDICTING THE MECHANICAL PROPERTIES OF NONWOVEN GEOTEXTILES WITH THE FINITE ELEMENT METHOD

A new computer model is developed to predict the tensile behavior of nonwoven fabrics from the stress-strain behavior of their constituent fibers and distributions of fiber orientation angles. The finite element method is used to calculate the numerical solution of stress and strain distribution in different regions of the samples during tensile deformation. Stress-strain curves of fabrics are simulated. Tensile testing is done on several nonwoven fabrics to verify the simulated results, which are in a good agreement with those obtained from tensile experiments.

Effect of Stacking Sequence on the Mechanical Properties of Glass–Carbon Hybrid Composites before and after Impact

Hybrid composites are susceptible to accidental low energy impacts from hazards such as tools dropping during maintenance, transportation debris and hailstones. These impacts can cause significant strength reduction and localized damage which is potentially a source of mechanical weakness especially for graphite composites. The effect of stacking sequence on mechanical properties of stitched composites is studied for low velocity impact damages. Tests were performed for the same volume fraction (Vf) with different hybrid sequence and ply angle. The incorporation of glass fibers in carbon reinforced structures improved impact properties and increased the strain to failure. The addition of carbon fibers to the surface of glass-reinforced composites increases the flexural modulus for undamaged samples. Tensile failure mechanism of damaged plies seems to be affected by the interaction of reinforcement property, hybrid order and ply angle.

Recovery and Reuse of Waste PVC Coated Fabrics. Part 1: Experimental Procedures and Separation of Fabric Components

The polyester in the base fabrics (PET) and the polyvinyl chloride coating (PVC) along with plasticizers and adhesive/glue were separated from a commercial coated fabric by a scheme of chopping, grinding, and extracting with a selected preferred aqueous MEK solution. A novel recovering method called swelling method is introduced to separate and reuse waste PVC coated PET fab rics. In comparison with other recycling techniques, the swelling method is a sim ple procedure with minimal environmental impact. The selection of the swelling agent of methylethyl ketone (MEK) was made after an analysis of the physical and chemical properties of several chemicals. Phase separation was found in the MEK/water system that serves as swelling bath. The two phases exist over a wide concentration range. The behavior of the swelling system and the swelling proper ties of recovered components were investigated by parameters, such as refractive index, swelling degree, and the average particle size of recovered PVC.