Daniel O Hare Adams

Bioabsorbable soy protein plastic composites: Effect of polyphosphate fillers on water absorption and mechanical properties

The use of synthetic and natural bioabsorbable plastics has been severely limited due to their low stiffness and strength properties as well as their strong tendency to absorb moisture. This research focused on the development of bioabsorbable polyphosphate filler/soy protein plastic composites with enhanced stiffness, strength, and water resistance. Bioabsorbable polyphosphate fillers, biodegradable soy protein isolate, plasticizer, and adhesion promoter were homogenized and compression-molded. Physical, mechanical, and water absorption testing was performed on the molded specimens. Results showed improvements in stiffness, strength, and water resistance with increasing polyphosphate filler content up to 20% by weight. Application of a coupling agent produced further mechanical property enhancements and a dramatic improvement in water resistance, interpreted by an interfacial chemical bonding model. Examination of the fracture surfaces of the materials revealed that the addition of the polyphosphate fillers changed the failure mode from brittle to pseudo-ductile. These results suggest that these materials are suitable for many load-bearing applications in both humid and dry environments where current soy protein plastics are not usable.

Effects of Layer Waviness on the Compression Strength of Thermoplastic Composite Laminates

Layer waviness was investigated in T300/P1700 carbon/polysulfone com posite laminates under static compression loading. A three-step procedure was used to fab ricate isolated layer waves into the central 0° layer of [902/02/902/02/902/ /02w]s laminates. Efforts were made to insure that this three-step procedure itself did not degrade the lami nate quality. Layer wave geometries up to 1.5 layer thicknesses in amplitude and as short as nine layer thicknesses in length were tested. The more severe wave geometries pro duced reductions in static strength as high as 36 % , although the wavy 0° layer accounted for only 20% of the load carrying capacity of the laminate. Specimen failures were sudden and catastrophic. Brooming failure, characterized by through-the-thickness splaying of the layers and numerous delaminations near the waviness, was the common failure mode.

Compression strength reductions in composite laminates due to multiple-layer waviness

Abstract The effects of multiple-layer regions of waviness on static compression strength were investigated. A single-step fabrication method was developed for fabricating multiple-nested wavy 0 ° layers into otherwise wave-free thermoset crossply laminates. Laminates were fabricated with varying percentages of 0 ° layers containing layer waviness, but all with a constant layer wave severity. Testing was performed to determine the effects of multiple-layer wave regions on compression strength. When no greater than 33% of the 0 ° layers contained waviness, the percentage reduction in compression strength was approximately equal to the percentage of wavy 0 ° layers. However, a constant strength reduction of approximately 35% was observed when more than 33% of the 0 ° layers contained waviness. These results suggest that under limited conditions, compression strength reductions due to layer waviness may be estimated by the percentage of 0 ° layers containing layer waviness.

Hydrophobic ear plugs

Ear plugs for swimming, snorkeling, scuba diving and other water related activities form a watertight seal within an individuals outer ear canals. The ear plugs have a lumen extending along the ear canal. A hydrophobic membrane extending across the lumen, which admits air into or out of the ear canal but blocks water, seals the ear against water but transmits air. This passage of air equalizes pressure across the plug, improves hearing with the ear plug in place, and prevents water contaminants, such as harmful infectious agents and pollutants, from entering the ear canal.

Effects of Layer Nesting on Compression-Loaded 2-D Woven Textile Composites

Layer nesting refers to the interaction between neighboring fabric layers of a textile composite laminate. Idealized layer nesting configurations were investigated in five-harness satin weave carbon/epoxy laminates under static compression loading. A methodology was developed to fabricate three idealized nesting cases: stacked, split-span, and diagonal. All three idealized nesting cases produced reductions in compressive strength and ultimate strain when compared to the conventional randomly-nested laminates. The diagonal nesting geometry produced the largest strength reductions. Finite element results showed consistent strength reduction trends for the idealized nesting cases; however, the magnitudes of compressive strengths were overpredicted. These results suggest that regions of idealized nesting in conventional woven composites, particularly diagonal nesting, may be sites of failure initiation. Additionally, differences in compressive strength associated with idealized nesting configurations may explain the considerable scatter observed in compressive strength for these materials.

Effects of layer waviness on the compression fatigue performance of thermoplastic composite laminates

The influence of layer waviness on the compression fatigue response of carbon/polysulphone composite laminates was studied. Specimens with a moderate level of layer waviness as well as wave-free control specimens were cycled to failure at a variety of maximum stress levels to establish S-N curves. A one and a half decade loss of compression fatigue life was observed for moderate layer wave specimens as compared with the control specimens. Brooming failure, characterized by through-the-thickness splaying of the layers and by numerous delaminations, was the common failure mode. The stress level corresponding to the 106 cycle run-out for these layer wave specimens was reduced to approximately 45% of the static compression strength of the wave-free laminate, as compared with a reduction to 75% for the control specimens. Moderate layer were specimens cycled to the 106 cycle run-out showed no evidence of delamination in the vicinity of the layer wave. Specimens with a mild layer wave failed in the grips away from the wave and exhibited fatigue life comparable to the wave-free specimens.

Boundary element analysis for composite materials and a library of green's functions

Abstract With the rapid development of advanced composite materials and the wide application of such materials in engineering, it is desirable to model problems involving these materials by computer and to use powerful numerical methods like the finite element method (FEM) and the boundary element method (BEM) for analysis. In this paper, a BEM is developed to analyze two-dimensional micromechanical behavior of fiber-reinforced composites based on models for both perfectly-bonded and imperfectly-bonded materials in a unit cell. For composites with perfect bond between matrix and fibers, it is shown that our predictions coincide satisfactorily with comparable quantities obtained in physical experiments and by FEM analysis. For imperfectly-bonded composites, it is found that variation of the interphase parameters (thickness, stiffness) causes pronounced changes in the overall effective moduli and also in the state of stress in the composites. Also in this paper, the idea of a library of Greens functions for fiber-reinforced composites is discussed. With such a library, users could quickly generate data useful in design with very little knowledge of methods for computational modeling in general or of the BEM in particular.

Analysis of Layer Waviness in Flat Compression-Loaded Thermoplastic Composite Laminates

A finite element analysis was used to investigate layer waviness effects in flat compression-loaded composite laminates. Stress distributions in the vicinity of the layer waves as well as the locations and modes of failure were investigated. Two layer wave geometries were considered, each modeled within an otherwise wave-free thermoplastic composite laminate. These two wave geometries, classified as moderate and severe, corresponded to layer waves fabricated in actual laminates and tested under uniaxial compression loading. Material nonlinearities obtained from intralaminar shear and 0 and 90 deg tension and compression testing were incorporated into the analysis. The nonlinearity observed in the intralaminar shear stress-strain behavior was assumed to be valid for interlaminar shear stress-strain behavior, and the nonlinearity observed in the 90 deg tension and compression stress-strain behavior was assumed to be valid for interlaminar normal stress-strain behavior. Failure was predicted using a maximum stress failure theory. An interlaminar tension failure was predicted for the severe layer wave geometry, producing a large compression strength reduction in comparison to the wave-free laminate. Fiber compression failure was predicted for the moderate layer wave, producing only a slight compression strength reduction. Although significant material nonlinearity was present in the interlaminar compression and shear response of the material, the inclusion of material nonlinearity produced only slight decreases in predicted compression strengths relative to predictions based on linear material behavior.

Influence of In-Plane Fiber Misalignment on Moiré Interferometry Results

Moiré interferometry is an experimental technique that is being viewed favorably for verifying analytical predictions of mechanical performance in composite materials. However, since interferometry measures displacements at a free surface, one must separate the effects due to fiber architecture from those due to free-edge effects. This paper addresses the influence of in-plane fiber misalignment on free-edge interlaminar shear strain. Experimental results for laminates with intentional fiber misalignment are compared to analytical predictions by using the finite element method. Small degrees of fiber misalignment are shown to produce large free-edge interlaminar shear strains. Thus, moiré interferometry results may not be quantifiable for nonidealized composites which exhibit in-plane fiber misalignment.

Effect of thickness variations on the sound radiation from beams

The effect that spatial thickness variations of a beam has on the beam’s far‐field sound radiation was studied. The steel beams that were used in the initial tests show that at low‐frequency ranges (500–1500 Hz) the thickness variations acted as discontinuities along the beam that increased sound radiation. However, at higher frequency ranges (2000–4000 Hz) the thickness variations, when spaced at certain intervals, acted as global stiffness changes and decreased the sound radiation. This decrease occurred when the spacing of the variations corresponded to a structural wavelength. Composite beams with thickness variations have also been built and tested. The spatial thickness variations appear to have a similar effect on the sound radiation as in the steel beams. The two data processing techniques used to evaluate the influence of the spatial thickness variations were a phase‐speed tracking filter to quantify wave propagation in the structure and a wave‐number domain filter to quantify far‐field radiation...