Douglas R. Carroll

Structural properties of recycled plastic/sawdust lumber decking planks

Abstract Plastic lumber is being used to replace wooden lumber in some construction applications, especially in outdoor applications where the plastic lumber is presumed to weather better than the wood. However, the structural properties of the plastic lumber are not well understood, and the use of plastic lumber in structural applications is not authorized in the common building codes. In this research effort, standard 2×6 plastic lumber planks were tested for many different structural properties. The plastic lumber tested was a blend of recycled plastic and sawdust. The tests were conducted at −23.3°C to simulate winter conditions, and at 40.6°C to simulate summer conditions. In all cases the high temperature strength and stiffness was lower than at low temperature, so the high temperature values would determine the allowable strength and stiffness for design. The high temperature modulus of the plastic lumber was 5.79, 1.03, and 1.12 GPa in compression, flexure and tension respectively. High temperature strength values were 16.8, 12.0, and 1.45 MPa in compression, flexure and tension respectively. The high temperature shear strength of the plastic lumber was 5.31 MPa. Strength tests were also performed for nail and screw connections typically used with lumber, and the pull-out and lateral load were comparable to wooden lumber. The plastic lumber performed well under sustained load tests at high temperature. Slip resistance tests were performed, and it was found that the plastic lumber is more slippery than wooden lumber, but probably does not represent a safety hazard. The conclusion was that the plastic lumber is a good structural material, but it is not appropriate to simply substitute plastic lumber for wooden lumber pieces of the same dimension in structural applications. Plastic lumber structures must be designed using the structural properties of the plastic lumber.

An initial stage model for the sintering of constrained polycrystalline thin films

Abstract A physical model has been developed for the initial stage of sintering of thin constrained polycrystalline films. The model compares the shrinkage of constrained thin films to the shrinkage of unconstrained or free sintering material. It predicts that the volumetric shrinkage of a constrained thin film will be slightly more than the linear shrinkage for the free sintering case, but far less than the volumetric shrinkage for the free sintering case. Model predictions show that the sintering of a constrained film is highly dependent on the ratio of the boundary energy to the surface energy, and on grain growth. The model was used to fit the experimental data of Garino & Bowen, for the sintering of constrained alumina and zinc oxide films ( Garino, T. & Bowen, H. K. , J. Am. Ceram. Soc., 70 (9) (1987) C210–211) .

Fabrication of hybrid ceramic matrix composites

The desire to improve the transverse properties and microcracking stress of unidirectional continuous fiber reinforced ceramic matrix composites has led to development of the hybrid ceramic matrix composite (HCMC). This paper discusses the techniques we used in the fabrication of HCMC specimens used for mechanical characterization.

Elastic properties of imperfectly bonded short fiber composites

The effect of debonding on various moduli of short fiber composites was studied by developing an analytical model. It was assumed that debonding of the fiber-matrix interface initiated at the end of the fibers and progressed to the center. Debonding along only a few percent of the fiber length substantially reduced the moduli of the composite, especially for relatively high-volume fractions of reinforcement. Results were compared to an existing model, in which debonding was assumed to occur in a sector around the fiber and all along the length of the fiber. It was found that debonding along the length of the fiber reduced the modulus of the composite significantly more than debonding around a sector, for the same percentage of the fiber debonded. It was not just the percentage of the fiber debonded which effected the moduli, but also the manner in which the debonding occurred.

Structural Properties of Recycled HDPE Plastic Lumber Decking Planks

Plastic lumber is being used to replace wooden lumber in some construction applications, especially in outdoor applications where the plastic lumber is presumed to weather better than the wood. However, the structural properties of the plastic lumber are not well understood, and the use of plastic lumber in structural applications is not authorized in the common building codes. Contractors who use plastic lumber in structural applications such as outdoor decks are in most cases violating the building codes. In this research effort, standard 1 2 6 tongue-in-grove plastic lumber planks were tested for many different structural properties. The tests were conducted at m 23.3°C to simulate winter conditions, and at 40.6°C to simulate summer conditions. In all cases the high temperature strength and stiffness was lower than at low temperature, so the high temperature values would determine the allowable strength and stiffness for design. The conclusion was that the plastic lumber is a good structural material, but that it is not appropriate to simply substitute plastic lumber for wooden lumber pieces of the same size in structural applications. The plastic lumber is not as strong and stiff as the wooden lumber, and so larger sizes must be used to obtain the same strength and stiffness. Because of the much lower modulus, compression members made from plastic lumber may need to be of much larger size to resist buckling.

Effect of interface debonding on various moduli of short fiber composites

The effect of debonding on various moduli of short fiber composites has been studied by developing an analytical model. It is assumed that debonding of the fiber/matrix interface initiates at the end of fibers, and progresses to the center, as predicted by classical shear-lag theory. Debonding along only a few percent of the fiber length substantially reduces the moduli of the composite material, especially for materials with high volume fractions of reinforcement. Degradation of the bonding can also lead to the growth of preexisting interface imperfections which can add to the deterioration of the material properties. Results are presented for the cases where the fibers are substantially stiffer than the matrix and where the matrix is stiffer than the fibers. It is also observed that a decrease in aspect ratio of the fibers leads to decrease in the moduli of the system in general.

Rolling of recycled plastic fibers

Abstract A model was developed for the processing of recycled plastic flakes into fibers to study the effect of the various processing parameters. Verification of the fiber rolling model was done by comparing it with the standard flat rolling model, i.e., rolling into flat sheets, by looking at the sample roll-face pressure distributions for the two processes. The roll-face pressure distribution for fiber rolling and flat rolling showed the same basic curve profile, but the fiber rolling had a higher magnitude for the pressure. It seemed reasonable that the rolling and cutting of the plastic into fibers would require a higher roll pressure than the rolling flat sheets. Rolling operations have a neutral point on the rolls, which is the point of maximum or peak pressure. The neutral point for fiber rolling is slightly nearer to the entry compared with flat rolling for the same percentage reduction in cross-sectional area. After verifying the fiber rolling model with the flat rolling model, a parametric study was performed on the fiber rolling model, which showed how the processing parameters affected the roll-face pressure distribution and the torque required to turn the rolls: the coefficient of friction between the rolls and the plastic flakes, the size and shape of the fibers created, the initial thickness of the plastic flakes, and the roll radius. The model was useful in understanding the basic science of the fiber rolling process, and would be useful in optimizing the design of a rolling mill if this is developed into a commercial process.