Thesis. 1980. Ph.D.--Massachusetts Institute of Technology. Dept. of Psychology. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND HUMANITIES. / Bibliography: leaves 46-51. / Ph.D.

Note:

No description available.

No description available.

No description available.

Pavement concrete joints are the weakest locations in concrete pavement systems. They are man-made cracks to accommodate concrete slab expansion and contraction due to temperature fluctuations. Sealant is usually used in pavement joints to prevent roadway debris, deicing chemicals, and moisture from entering the joint. When sealant fails, the pavement deteriorates rapidly; and when joint sealant performs adequately, the pavement preserves its intended performance. In the field, joint sealant undergoes two types of mechanical loading simultaneously. The sealant is experiencing tension or compression as slabs contract (low temperature) or expand (high temperature), respectively. Sealants also experience shear as heavy trucks travel over the joint and deflect the ends of the pavement slabs. In addition, sealants may also be exposed to a variety of environmental conditions, such as moisture, ultraviolet light, and jet fuel, which in some cases could be detrimental to their performance. In this study, the effects of vehicular and environmental loading on joint sealant performance were evaluated. To simulate the sealed joint performance, specimens were constructed by sandwiching a sealant between two 50.8 mm Portland cement concrete (PCC) cubes. Prior to mechanical loading, specimens were subjected to partial immersion in distilled water, partial immersion in jet fuel, and/or exposure to UV-A light. The specimens were then subjected to static horizontal tension, simulating slab contraction, and cyclic deflection-controlled shear, simulating heavy trucks travelling over the joint. The cycle consists of one 0.2 second period of sinusoidal loading (total 6.4 mm deflection) followed by a 0.4 second relaxation. The mechanical loading was applied using a special fixture developed at Virginia Tech, which is connected to a closed-loop servo-hydraulic loading machine. Two types of sealants (preformed neoprene and field-molded silicone with a primer) were tested using PCC mixes with two different aggregate types. In, addition, two different joint widths were evaluated for each sealant type. From the results of the cyclic testing and environmental conditioning, it was shown that the use of a primer greatly enhances the performance of the silicone sealant used with concrete containing limestone aggregate. In addition, severe swelling occurs when silicone sealant is exposed to jet fuel, and the failure of the field-molded silicone initiated at the bottom of the sealant and propagated upward. The preformed neoprene sealants proved very durable despite any combination of environmental conditioning, provided that the sealant remained in compression. / Master of Science

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

To make low grade lumber into high-valued products, finger-jointing is a widely used method in the timber industry. In certain situations, chip-out occurs degrading the quality of the joint. To better understand the machining process, a beam-type dynamometer based on strain gages was designed to analyze the dynamic cutting forces parallel and vertical to the feeding direction. The test results indicate that the dynamometer design was sensitive enough to measure small force changes at relatively high frequencies during the cutting operation. The test conditions were set as close as possible to that in industry. Cutting force behavior of the rotating cutterhead was examined, and test samples with different fiber angles were used for inspecting the influences on the chip-out occurrence and cutting forces. The results show that cutting forces are determined by the density of the wood and the maximum chip thickness. Slight differences in tool shape and the balance of the cutterhead can vary the cutting force behavior. The occurrence of chip-out is dependent on the fiber angle and the chip thickness. No relationship between chip-out and cutting force was found, within the sensitivity of the dynamometer. Fiber angle has some effect on the cutting force, and also influences the cutting surface quality. A high speed video camera was also employed to visually observe the formation of chip-out. Frame by frame analysis showed that the chip-out occured when a knife passed through the trailing edge of the cut-block, and the failure developed in the sequel cuts. Cutting force and chip-out models were developed from the experiment results, and can be used to reduce chip-out and increase recovery during finger-jointing in ponderosa pine cut-stock operation. / Graduation date: 1993

This paper presents the development of a finite element method for modeling fastener joints in aircraft structures. By using connector element in commercial software Abaqus, the finite element method can handle multi-bolt joints and secondary bending. The plates in the joints are modeled with shell elements or solid elements. First, a pre-study with linear elastic analyses is performed. The study is focused on the influence of using different connector element stiffness predicted by semi-empirical flexibility equations from the aircraft industry. The influence of using a surface coupling tool is also investigated, and proved to work well for solid models and not so well for shell models, according to a comparison with a benchmark model. Second, also in the pre-study, an elasto-plastic analysis and a damage analysis are performed. The elasto-plastic analysis is compared to experiment, but the damage analysis is not compared to any experiment. The damage analysis is only performed to gain more knowledge of the method of modeling finite element damage behavior. Finally, the best working FE method developed in the pre-study is used in an analysis of an I-beam with multi-bolt structure and compared to experiments to prove the abilities with the method. One global and one local model of the I-beam structure are used in the analysis, and with the advantage that force-displacement characteristic are taken from the experiment of the local model and assigned as a constitutive behavior to connector elements in the analysis of the global model.