Final Laminate Research Articles

Influence of Stacking Sequence and Fiber Orientation of Failure Behavior of Symmetric Angle-Ply Laminates.

The failure behavior of symmetric angle-ply laminates under a uniform axial strain was elucidated with special emphasis on the effects of the stacking sequence and fiber orientation. Three basic failure modes, fiber breakage, matrix failure and delamination, are considered. Failure criteria are established in term of quadratic stress polynomials according to the three basic failure modes. The variations of the stress distributions near the free edges are illustrated through the application of a quasi-three-dimensional FEM with a four-node rectangular element. On the basis of the proposed failure criteria and the postfailure analysis, the failure modes are distinguished, the progress of failure to final laminate failure is traced, and the ultimate strength of laminates is obtained. A good agreement is obtained with experimental results found in the literature.

Effect of the Interfacial Interleaf to the Interlaminar Fracture and Intralaminar Fracture of a New BMI Matrix Composites System

Systematic studies were conducted to investigate the effect of the introduc tion of a soft thermoset adhesive layer at appropriate interface to the interlaminar fracture and intralaminar fracture of the BMI matrix based composite laminates. Tests include DCB and ENF tests for measuring interlaminar fracture toughnesses, quasi static tension test on the crossply laminates and edge delamination test for measuring matrix crack initi ation, edge delamination onset, mixed-mode interlaminar fracture toughness and the ulti mate laminate strength. The improvements of the interlaminar fracture toughnesses of the GFRP and CFRP laminates are significant. An elastic foundation beam model is intro duced to analyze the interleaved DCB specimen. Results show stress concentration at the crack-tip of the interleaved DCB specimen is reduced. Besides the factor of the possible formed plastic zone in interleaf, the modified interlaminar bond strength of the adhesive/ composites interface may lead to higher interlaminar fracture toughness. The edge delamination strength and the mixed-mode interlaminar fracture toughness in interleaved laminate are raised significantly. However, the interleaf has no significant effect on the laminate strength because the interfacial interleaf only improves the interlaminar fracture feature while the final laminate fracture is controlled by the intralaminar properties of the lamina. On the matrix cracking in interleaved laminate, both the matrix crack growth rate and its final saturation crack density decrease in the interleaved multidirectional laminate. The matrix crack was found to initiate early in the interleaved crossply laminate. This*Author to whom correspondence should be addressed Journal of REINFORCED PLASTICS AND COMPOSITES, Vol. 13-June 1994 0731-6844/94/06 0509-32 $6.00/0 @ 1994 Technomic Publishing Co., Inc.result agrees with the analysis of the one-dimensional shear-lag model. But in the edge delamination specimen, matrix crack initiation is raised by the interleaf.

Fracture Behavior of a Fiber-Reinforced Titanium Matrix Composite with Open and Filled Holes at Room and Elevated Temperatures

A study was conducted to experimentally investigate the fracture behavior of a titanium-based metal matrix composite (MMC), SCS-9/β21s, with open and filled holes subjected to static tensile load. This study was conducted with unidirectional, crossply, and quasi-isotropic laminates. Unnotched and notched coupons having specimen width to hole diameter ratio of six were tested at room temperature, 482°C, and 650°C. Pins of materials 7075-T6 and Mar-m-246 were employed for filled hole tests. Tests were also conducted on unnotched off-axis and angle-ply laminates to obtain experimental data for the shear strength and the shear modulus of the laminae. Material integrity, residual stresses, interfacial failures, failure progression, and notch sensitivity of the tested MMC were addressed. The molybdenum ribbon was found to have a significant impact on the damage initiation and integrity of the MMC. The release of residual stresses and interfacial failures gave rise to a bilinear stress strain curve in laminates with off-axis plies. Final laminate response was governed by nonlinear behavior caused by debonding and failure of 0° fibers in conjunction with plasticity in the matrix material. All fracture surfaces exhibited ductile fracture due to tensile overload. Matrix cracking occurred at loads higher than 80% of the failure strength in the 650°C tension specimens. Matrix cracking did not occur at the other temperatures. Laminates displayed notch sensitivity at room temperature and 482°C. At 650°C the laminates displayed much less notch sensitivity; or, the laminates were much less sensitive to the existence of the hole. The insertion of pins into open holes had negligible effect on the stiffness, strength, and failure progression of the laminates at room and elevated temperatures.

The influences of contamination during lamination on the properties of composite materials

The quality of a fibrous composite laminate can be largely attributed to the laminating process. It is therefore important to control parameters which will ultimately affect the desired quality of the laminate. Although several composite manufacturing organisations have installed clean room facilities with the hope of controlling potential contaminants, which may be detrimental to the process, the unavoidable reductions in productivity, coupled with the initial capital and maintenance costs make it an expensive solution to an unquantified problem. This study investigates the influences of contamination on structural fibre reinforced composites. Initial testing has involved contaminating Carbon/Epoxy (Fiberite 7714B) prepregs on a gross level. Contaminants have been selected on a tactile level in order to be as closely representative of situations likely to be encountered in the laminating process. The research has concentrated on airborne particulates, including fibres, condensation and humidity. Modes of contamination have been proposed for each, and suitable test methods selected to verify the modes. Test methods include the sort beam shear test (interlaminar shear strength), double cantilever beam test (interlaminar fracture data) and tensile tests. Such high levels of contamination enables the identification of those contaminants that are most detrimental to final laminate quality. Strategic reduction in the contamination levels of those identified will enable the clean room operating level to be sought

Autoclave Processing of PEEK/Carbon Fiber Composites

The influence of processing conditions on the laminate quality for auto claved carbon fiber reinforced polyetheretherketone (PEEK) has been studied. The pro cessing temperature, pressure, and hold-time were the major variables examined, and their influences on the structure and properties for an 8-ply thick laminate were investigated. The structural evaluation performed on a macroscopic level in terms of compaction, resin/fiber homogeneity and void content, as well as morphological studies, showed a well-defined lower processing temperature limit at approximately 375°C, for satisfactory laminate quality. The lower processing temperature limit was also corroborated by the fracture toughness properties of the laminate. Contrary to processing temperature, pro cessing pressure and hold-times showed a secondary influence on the final laminate quality.

Laminated motor pole assembly using welded studs and its effect on interlaminar resistance

A method for laminated assembly manufacturing by welding the studs at each end of the assembly is investigated. Results of tests carried out to determine the tightness of the assembly are presented, and the fabrication process is described. A method is presented for calculating the final stud stretch, given the total force exerted, stud diameter, and stud material grade and length. From these calculations and graphical data of press tonnage vs. pole movement, the final pole lamination pressure can be predicted. It is concluded that this method is desirable in all respects over the existing rivet methods and continuously welded methods. >

Foam‐backed and Coated Fabrics

The combination of textile fabrics either to other textiles or to plastics materials has opened up new fields. The pace of development during the past fifteen years has been spectacular. Some of the most interesting advances have been made in the field of expanded plasties, especially expanded vinyls and polyurethanes, and we are really only at the beginning. In this paper an attempt has been made to outline the main methods used for combining textile and plastics materials. This has been followed by a short description of the methods used to produce expanded vinyls. The main part of the paper deals with the development of flexible polyurethane foams, their combination to textile materials, and the evaluation of the final laminate. The field of expanded plastics is latent with possibility; some applications have been indicated.