The effect of uni-directional stress on the electrode potential of copper in aerated potassium nitrate solutions was studied. The influence of the variables time, temperature, concentration, magnitude of stress, mechanical condition of the metal, and pH was considered. The potential difference between two size #22 B & S copper wires was continuously recorded on a type G Speedomax automatic recorder. A balance pan was attached to one of the wires to which weights were added and the change in the potential difference between the two wires from the pre-stress potential difference was taken as the strain potential. At least four runs, using fresh pairs of wires for each run, were carried out to illustrate each specific point and to show the results have statistical significance and are reproducible. The following results were obtained: (A) Electronegative strain potentials have been obtained for copper metal in aerated potassium nitrate solution; these changes achieve a maximum at the instant of stressing and then decay with a negative acceleration with time. After an initial period of time, the strain potential decayed logarithmically with time. The magnitude of the electronegative strain potential for a given stress increased exponentially with the reciprocal of the absolute temperature and remained essentially unchanged for concentration changes ranging from 0.005N to 0.500N. (B) Experimental evidence was obtained to support the postulate that strain potentials of copper metal in aerated potassium nitrate solution and their time dependence parallel film rupture; the effect of the change in internal energy due to plastic deformation cannot be ignored. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

published_or_final_version / Dentistry / Doctoral / Doctor of Philosophy

published_or_final_version / Dentistry / Master / Master of Dental Surgery

The torsion test was evaluated as a method for determining the shear strength of full-size structural lumber. The evaluation involved an experimental length study, an experimental depth study, and a finite element study. The length study consisted of fifty nominal 2x4 specimens, ten specimens for each length, and ten American Society for Testing and Materials (ASTM) shear blocks. One 14 foot long board yielded one specimen for each length: (a) 21.0", (b) 28.5", (c) 32.0", (d) 35.5", (e) 39.0", and (f) an ASTM D143-94 shear block. The statistical analysis revealed no evidence that the length affected the shear strength. The depth study consisted of fifty specimens, ten specimens for each depth: (a) 2x4, (b) 2x6, (c) 2x8, (d) 2x10, and (e) 2x12. In addition, fifty ASTM shear blocks, one block for each specimen, were tested. The statistical study did not reveal convincing evidence of a depth effect on shear strength, even after accounting for specific gravity and shear span as covariates. Failure modes for the torsion samples involved a longitudinal shear crack at the mid-point of the longest side, which propagated toward the ends of the specimen and through the cross section perpendicular to the growth rings. The finite element model revealed that uniform shear stress occurs within the shear span, which begins and ends a distance of approximately two times the depth plus the grip distance away from each end of the member. In addition, torsion theory verified that the experimental shear failure plane that occurs within the shear span is parallel to the grain and the shear slippage is also parallel to the grain, similar to the known shear failure in specimens subjected to bending loads. Based on the results of this study, the torsion test is the best practical method to determine the pure shear strength of full-size structural lumber, because the test yields 100% shear failures and the specimen is in a state of pure shear stress. / Graduation date: 1998

It is important in structural analysis and design, whether deterministic or reliability-based, to know the level of uncertainty for the methods of strength prediction. The uncertainty associated with strength prediction is the result of ambiguity and vagueness in the system. This study addresses the ambiguity component of uncertainty; this includes uncertainty due to randomness in the basic strength parameters (random uncertainty) and systematic errors and scatter in the prediction of strength (modeling uncertainty). The vagueness component is briefly discussed. A methodology for quantifying modeling and random uncertainty is presented for structural failure modes with a well defined limit state. A methodology is also presented for determining the relative importance of the basic strength parameters in terms of their importance to the total random uncertainty. These methodologies are applied to the compressive failure of longitudinally stiffened panels. The strength prediction model used in this analysis was developed in the UK and is widely used in analysis and design. Several experimental sample sets are used in the analysis. Mean values and coefficients of variation are reported for the random and modeling uncertainties. A comparison with results from other studies with several strength prediction algorithms is undertaken for the modeling uncertainty. All of these studies involve longitudinally stiffened panels which fail in axially compressive collapse. Ranges for the mean and coefficient of variation of the modeling uncertainty are presented. / Master of Science

Results of an experimental study of the failure and crippling of thin-walled open section prismatic compression members are presented. Twenty-four specimens were tested, 13 of which were channel sections and the other 11 were zee sections. Three specimens were made of 2024-T3 aluminum. The remaining 21 specimens were made of AS4-3502 graphite-epoxy. All specimens were tested to failure. Seventeen specimens exhibited local buckling of flanges and webs prior to failure, four exhibited global column buckling prior to failure, two exhibited material short column failure, and one exhibited unstable postbuckling behavior prior to failure. The buckling loads for each specimen were also calculated by a computer code and compared to experimental buckling loads. Good correlation was achieved for specimens that did not buckle as columns. The graphite-epoxy specimens which buckled locally had significant postbuckling response prior to failure at a maximum load (crippling). Differences in the crippling failure and compressive strength failure are discussed for the graphite-epoxy specimens. / Master of Science

In an effort to obtain an improved mode III fracture toughness test suitable for a testing standard, mechanics analysis, experimental testing, and finite element analysis (FEA) have been conducted. Of particular concern are the merits of one-point and two-point edge crack torsion (ECT) test methods, the influence of specimen geometry that overhangs beyond load/support points, and the influence of crack length on the compliance and energy release rate. Shear stress distributions at the crack front are determined to examine the uniformity of mode III loading and mode II influence. The shear stress distributions in the one-point and two-point tests are virtually identical, indicating that either of the two tests could be used interchangeably. Based on the uniformity of the mode III shear stress distribution along the crack front, it was found that the ECT specimen should have minimum overhang. Longer crack lengths tend to produce nonuniform shear stress distributions. A modified two-point ECT test fixture was developed to allow testing of specimens with a range of dimensions. This development enabled experimental verification of the results from the FEA overhang series. The specimens with a minimum overhang produced consistant mode III toughness data. The most reliable way to reduce data is through the original compliance calibration method. A modified ECT specimen was developed with a staggered crack front to produce uniform mode III crack growth. Finite element analysis of the modified ECT specimen shows a uniform mode III stress distribution along the crack front with little mode II interaction. / by Grant Browning. / Thesis (M.S.C.S.)--Florida Atlantic University, 2009. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web.

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2017. / Material testing is an important test to researchers in material science fields and other engineering related fields. This is the base for material evaluation prior to the application. This test is used in the engineering field to determine the strength of materials which is an aspect of assigning materials to different functions. The uniaxial tensile testing of material is the most common form of testing the strength of metallic material - usually to investigate whether or not the material is worthy of the intended application. Material testing is normally performed under uncontrolled conditions in most laboratories. Numerous attempts had been previously made in attempt to control the temperature conditions when performing the tensile test on special materials such as shape memory alloys (SMA) and other smart materials. Various methods had been employed to control the temperature during tensile testing, methods such as induction heating, warm liquid baths, etc. The aim of this study was to develop a temperature controlled environment for the Houndsfield tensile testing machine which is found at the Cape Peninsula University of Technology in the Mechanical Engineering Department workshop. This was achieved through designing and manufacturing of a thermally controlled chamber -better known as a furnace. This chamber was tested for the optimal combination of proportional, integral and derivative parameters which were tuned on the proportional integral derivative (PID) controller. Performing the tensile test under controlled thermal conditions will allow the analysis of SMAs and other materials behaviour at different temperatures. With the aid of the manufactured chamber, the superior features of the SMA will be able to be studied. The manufactured thermal chamber which is electrically powered is insulated with a special ceramic refractory material to prevent the heat from escaping the chamber. The PID controller was used to control the temperature and heating elements act as the heat source. The manufactured chamber could withstand the maximum temperature 350oC that it was initially designed for. However, the challenge of having the specimen to be tested fully inside the chamber was overcame by designing specimen connectors that connected the specimen to the tensile testing machine. Tensile tests were conducted on the SMA wire at room temperature and other various controlled temperatures and different behaviours were observed on the stress-strain graphs.