James N. Craddock

Interactive multimedia labware for strength of materials laboratory

A CD‐ROM–based laboratory manual for the torsion experiment in the Strength of Materials Laboratory was developed through collaboration between Civil Engineering and the Interactive Multimedia Department. The labware is intended to enhance student learning through the development of and exposure to richer learning tools, resources, and advanced technologies.

Evaluation of InSpectra UV Analyzer for measuring conventional water and wastewater parameters

Abstract A relatively new analytical instrument for the measurement of 5-day biochemical oxygen demand (BOD 5 ), chemical oxygen demand, total suspended solids (TSS), total organic carbon (TOC), nitrates and surfactants has been developed commercially. It is based on the use of ultraviolet spectrophotometry and a deterministic approach to analyze the samples spectrum by comparing it with a series of historical reference spectra. Using standard methods for the measurement of BOD 5 , TSS and TOC as true values, the use of this instrument was evaluated. The samples tested were obtained from both wastewater and water treatment facilities. Results indicate that the BOD 5 measurement performed best. There was no correlation found for TSS or TOC.

The bending stiffness of laminated composite material I-beams

Abstract The bending behavior of graphite-epoxy I-beams was examined. The beams used in this study were made of T 300 934 graphite-epoxy with three different layups. Short-beam shear tests, using three-point bending, were used. The shear-deflection and bending-deflection contributions were separated using Timoshenko Beam Theory. The equivalent bending stiffness was obtained from the deflection due to bending. The bending stiffness was calculated in two ways: using a method based on lamination theory, and using a transformed-section method developed especially for composites. A comparison of analytical and experimental results indicates that both methods are accurate tools for predicting the bending stiffness of composite material beams.

Bending and transverse shear stresses in fiber-composite beams by the transformed-section method

Abstract A method to determine bending and transverse shear stress distributions in beams composed of fiber-composite layers is presented. The method is based on the transformed-section concept and takes into account the effects of Poissons ratios and in-plane shear coupling. To demonstrate the feasibility of the transformed-section model, numerical solutions are presented for three rectangular and I-shaped cross-sections. It is shown that for bending moments the transformed-section model presented herein is entirely consistent with the lamination theory. The model can also be used to determine the transverse shear stresses, and it is shown that the accuracy of the results may be significantly affected when the effects of Poissons ratios and in-plane shear are neglected in the analysis.

Behavior of composite laminates after first-ply-failure

Abstract The optimum use of composite laminates involves predicting both first-ply-failure (FPF) and the subsequent behavior of the laminate. Several theories have been proposed to model the behavior of a ply after it fails. Three of these theories are examined here. They include modeling the lamina behavior as elastic-perfectly plastic; as a strain hardening material, as a material which unloads through a negative tangent modulus. These three methods are used to predict the ultimate strength of various laminates. Results are compared to experimental results. Although none of these approaches is totally accurate, the elastic-perfectly plastic model seems to give the best results.

Modeling Elastic-Plastic Behavior of Metal-Matrix Composites with Reaction Zones Under Longitudinal Tension

Micromechanical models for the prediction of the longitudinal strength of metal-matrix composites are often based on one constituent reaching its elastic limit. This procedure can grossly underestimate the useful or effective strength of the composite. At elevated temperatures, the yield strength of the matrix material can become very low relative to the strength of the fiber (in extreme cases as low as 5-10 % of the fiber value). Even though the matrix has yielded, further load can be carried by the fibers. The problem can be further complicated by the formation of a third phase or a reaction zone between the matrix and the fiber. The fact that this reaction zone has distinct material properties must be accounted for in any analysis. To get a valid picture of the composites true load carrying ability the complete elastic-plastic stress-strain behavior must be studied. This paper presents results of such analyses for a system with a monotonically increasing load up to failure of the first constituent. The three constituents are modeled as strain-hardening materials. Results are first obtained for a simple bilinear model of the stress-strain be havior in each material. A more detailed study was also conducted in which the three materials were modeled with curvilinear post-yield behavior. Results are presented for some representative constituent material properties. These results indicate the methods of analyses outlined in this paper are valid and easy to use. The results also clearly show that the entire elastic-plastic stress-strain behavior of the metal-matrix composite is more im portant than simply determining the initial yielding of one component. Strength predic tions based on the first component yielding are seen to be often far too conservative.