Thesis: M.S., Massachusetts Institute of Technology, Department of Civil Engineering, 1980 / Bibliography: p. 553. / by Kevin Joseph O'Reilly. / M.S. / M.S. Massachusetts Institute of Technology, Department of Civil Engineering

This paper is a bachelor thesis in machine design where screaming screw tightenings are discussed. The research was initiated with a preliminary study in screw mechanics and the tightening process, as well as the stick-slip phenomenon. Furthermore, interviews were conducted with people at Scania and Atlas Copco who have relevant experience in screaming screw tightenings. These interviews strengthened the theory that screaming is caused by stick-slip. The natural frequency of a screw joint with a M8 x 60 mm screw and M8 M6M nut were approximated with FEM-analysis in Ansys. This in order to provide data for comparison with measured screams in future practical tests. The initial hypothesis that stick-slip causes scream was considered plausible since the natural frequency for the screw joint’s torsional oscillation is within the audible range. / Denna rapport är ett kandidatexamensarbete i maskinkonstruktion där skrikande skruvdragningar undersöks. Undersökningen inleddes med en förstudie i skruvens mekanik och åtdragningsprocessen. Stick-slip-fenomenet har även undersökts i förstudien. Vidare har intervjuer gjorts med personer som har erfarenhet inom området på Scania och Atlas Copco. Dessa intervjuer stärker teorin om att skrikfenomenet orsakas av stick-slip. Egenfrekvenser för ett skruvförband med dimensionerna M8 x 60 mm för skruven och M8 M6M för muttern togs fram genom en FEM-analys i Ansys. Detta för att i framtida praktiska tester kunna jämföra dessa frekvenser med uppmätta skrik. Den ursprungliga hypotesen om att stick-slip orsakar skrik bedömdes rimlig då egenfrekvensen för skruvförbandets torsionssvängning faller inom det hörbara intervallet.

At the calculations group in Sigma Industry East North, the traditional method for evaluating fasteners has been by use of the VDI2230 manual. As the complexity of a model increases the evaluation also becomes harder. The goal of this thesis is to set a robust evaluation method by combining the VDI2230 with the Finite Element (FE) method. Varied topics such as fastener and plate compliance, embedding effect, forces through the fastener and plate, minimum thread engagement length, service loads and the fatigue effect in fasteners is discussed. The flowchart discusses the process flow, as in, where to use the VDI2230 and where the FE method comes into use. The thesis also helps to understand designing of bolts like selection of the bolt diameter of varied applications and is user friendly to handle. The focus is also on reducing the time taken for fastener evaluation and setting up of an in-house technique for the evaluation. The evaluation method is verified using a test case. / På beräkningsgruppen på Sigma Industry East North har den traditionella metoden för utvärdering av fästelement varit att använda sig av manualen VDI 2230. Ökad komplexitet gör utvärderingen svårare att genomföra. Målet med detta examensarbete är att föreslå en robust utvärderingsmetod som kombinerar VDI 2230 med Finita Element-Analys (FEA). Olika ämnen såsom vekhet för fästelement och plåtar, sättningar, kraftvägar genom fästelement eller plåtar, minsta ingreppslängd, laster och utmattningseffekter diskuteras. Flödesdiagrammet avhandlar processflödet, det vill säga var man ska använda VDI2230 och när FE-metoden bör användas. Examensarbetet är också till för att skapa förståelse för hur man konstruerar skruvar, såsom val av skruvdiameter vid olika tillämpningar. Fokus har också varit att minska tidsåtgången för utvärdering av fästelement och att sätta upp tekniker för utvärdering att användas i den dagliga verksamheten. Utvärderingsmetoden verifieras med hjälp av ett provfall.

Bone mechanics and traditional implant materials produce a recurring problem for patients of total hip arthroplasty (THA): the bone is “shielded” from the loading it has become accustomed to over many years of development. Bone adheres to what is called “Wolff’s Law”, meaning it is an adaptive structure which adjusts its geometry based on the loads experienced over its life (Pearson; Goldstein). As the new femoral hip implant transmits reduced stresses to the remaining bone, bone tissue atrophies at the interface, permitting loosening of the implant, pain, and thereby obliging additional surgery to correct the issue (Meade). In the present work, a methodology is endeavored for creating an innovative design for femoral hip implants. The approach uncouples the finite element implant model from the bone model, in order to focus solely on expected behavior within the implant while considering the varying material behavior in unique directions and locations. The implant’s internal geometry is optimized in order to better match typical, intact bone conditions. The eventual design reduces extreme changes in stresses within remnant bone such that the implant will remain implanted for greater periods of time without additional surgical attention.

An experiment was performed to evaluate the relations between active range of motion (ROM) and upper limb anthropometric dimensions. Eight anthropometric dimensions, forearm length, distal and proximal forearm circumferences, wrist breadth, wrist thickness, wrist circumference, hand breadth, and hand length in combination with gender, wrist position, and direction of motion or exertion were evaluated to determine their effects on instant center of rotation (ICOR) and the magnitude of force exertion. The knowledge gained from analysis of the study data will be the first step in the formulation of a biomechanical model of wrist flexion and extension. Such a model would predict forces and torques at specific wrist postures and be employed to reduce cumulative trauma disorders of the wrist. Sixty right-hand dominant subjects (30 male, 30 female) between 20 and 30 years of age all reporting no prior wrist injury and good to excellent overall physical condition, were employed in this study. The upper limb anthropometric dimensions and ROM were measured and recorded for each subject. The anthropometric dimensions were compared to tabulated data. The measured active ROM values were compared with values in the literature. Correlation coefficients between pairs of anthropometric variables (by gender) were calculated. The mean active ROM measures, 164.0 deg for females and 151.8 deg for males, were significantly different (<i>Z</i> = 2.193, <i>p</i> = 0.014). The relationships between the anthropometric variables and active ROM were analyzed by three methods: correlation between ROM and each anthropometric dimension, prediction (regression) equations, and analysis of variance (ANOVA). No correlation coefficient between ROM and any anthropometric dimension was greater than 0.7. No prediction equation, based upon linear and quadratic combinations of anthropometric dimensions variables, was above the threshold of acceptability (<i>R²</i> ≥ 0.5). The results of the ANOVA showed a significant effect for gender. The ICOR had been hypothesized to be either in the head or neck of the capitate. The Method of Reuleaux was employed to locate the leOR points for flexion and extension (over the ROM) of the wrist with three load conditions, i.e., no-load, palmar resistance, and dorsal resistance. Analysis of the data, using ANOYA, showed that wrist position was the only significant variable. Thus, in future wrist models, the assumption cannot be made that the wrist is a pin-centered joint for flexion and extension. The static maximal voluntary contractile forces that can be generated by recruiting only the six wrist-dedicated muscles in various wrist positions were measured. There was a significant gender difference for the mean flexion force (<i>Z</i> = 4.00, <i>p</i> = 0.0001) and for the mean extension force (<i>Z</i> = 4.58, <i>p</i> = 0.0001). Females averaged 76.3 percent of the mean male flexion force and 72.4 percent for extension. The force data, categorized by gender, were then analyzed using three methods: correlation of variable pairs, regression equations, and ANOVA. None of the eight anthropometric dimensions and ROM was correlated with flexion or with extension force at an acceptable level. The prediction equations, linear and quadratic combinations of all possible subsets of anthropometric dimension values, ROM, and wrist position did not meet the minimum acceptable level of <i>R²</i> ≥ 0.5. The ANOVA procedure showed gender, wrist position, direction of force exertion, and the wrist position interaction with direction to have significant effects upon maximal force exertion. / Ph. D.

Difficulties in characterizing the dynamic behavior of wood structures have hindered investigations into their performance under dynamic loading. Because of this, wood structures are treated unfavorably in seismic design codes, even though past damage assessment surveys after seismic events indicated generally satisfactory performance. To allow investigations into their performance and safety under dynamic loading, the energy dissipation mechanisms of wood joints and structural systems must be known and the hysteretic behavior modeled properly. This thesis presents a general hysteresis model for wood joints and structural systems, based on a modification of the Bouc-Wen-Baber-Noori (BWBN) model. The hysteretic constitutive law, based on the endochronic theory of plasticity and characterized by a single mathematical form, produces a versatile, smoothly varying hysteresis that models previously observed behavior of wood joints and structural systems, namely, (1) nonlinear, inelastic behavior, (2) stiffness degradation, (3) strength degradation, (4) pinching, and (5) memory. The constitutive law takes into account the experimentally observed dependence of wood joints' response to their past history (Le., the input and response at earlier times, or memory). Practical guidelines to estimate the hysteresis parameters of any wood joint or structural system are given. Hysteresis shapes produced by the proposed model are shown to compare reasonably well with experimental hysteresis of wood joints with: (1) yielding plate, (2) yielding nails, and (3) yielding bolts. To demonstrate its use, the proposed model is implemented in a nonlinear dynamic analysis program for single-degree-of-freedom (SDF) systems. System response from arbitrary dynamic loading, such as cyclic or earthquake-type loadings, can be computed. Three SDF wood systems are subjected to the Loma Prieta accelerogram to obtain their response time histories. Advantages of using the proposed model over currently available models in nonlinear dynamic analysis of more complex systems are identified. A multidegree-of-freedom shear building model incorporating the proposed hysteresis model is formulated but not implemented on a computer. / Master of Science

Silver sintering technology has received considerable attention in recent years because it has the potential to be a suitable interconnection material for high-temperature power electronic packaging, such as high melting temperature, high electrical/thermal conductivity, and excellent mechanical reliability. It should be noted, however, that pressure (usually between three to five MPa) was added during the sintering stage for attaching power chips with area larger than 100 mm2. This extra pressure increased the complexity of the sintering process. The maximum chip size processed by pressure-free sintering, in the published resources, was 6 x 6 mm2. One objective of this work was to achieve chip-attachment with area of 13.5 x 13.5 mm2 (a chip size of one kind of commercial IGBT) by pressure-free sintering of nano-silver paste. Another objective was to fabricate high-power (1200 V and 150 A) multi-chip module by pressure-free sintering. In each module (half-bridge), two IGBT dies (13.5 x 13.5 mm2) and two diode dies (10 x 10 mm2) were attached to a DBC substrate. Modules with solder joints (SN100C) and pressure-sintered silver joints were also fabricated as the control group. The peak temperature in the process of of pressure-free sintering of silver was around 260oC, whereas 270oC for vacuum reflowing of solder, and 280oC under three MPa for pressure-sintering of silver. The process for wire bonding, lead-frame attachment, and thermocouple attachment are also recorded. Modules with the above three kinds of joints were first characterized by electrical methods. All of them could block 1200 V DC voltage after packaging, which is the voltage rating of bare dies. Modules were also tested up to the rated current (150 A) and half of the rated voltage (600 V), which were the test conditions in the datasheet for commercial modules with the same voltage and current ratings. I-V characteristics of packaged devices were similar (on-resistance less than 0.5 mohm). All switching waveforms at transient stage (both turn-on and turn-off) were clean. Six switching parameters (turn-on delay, rise time, turn-off delay, fall time, turn-on loss, and turn-off loss) were measured, which were also similar (<9%) among different kinds of modules. The results from electrical characterizations showed that both static characterizations and double-pulse test cannot be used for evaluating the differences among chip-attach layers. All modules were also characterized by their thermal performances. Transient thermal impedances were measured by gate-emitter signals. Two setups for thermal impedance measurement were used. In one setup, the bottoms of modules were left in the air, and in the other setup, bottoms of modules were attached to a chiller (liquid cooling and temperature controlled at 25oC) with thermal grease. Thermal impedances of three kinds of modules still increased after 40 seconds for the testing without chiller, since the thermal resistance of heat convection from bottom copper to the air was included , which was much larger than the sum of the previous layers (from IGBT junction, through the chip-attach layer, to the bottom of DBC substrate). In contrast, thermal impedances became almost stable (less than 3%) after 15 seconds for all modules when the chiller was used. Among these three kinds of modules, the module with pressure sintered joints had the lowest thermal impedance and the thermal resistance (tested with the chiller) around 0.609oK/W, In contrast, the thermal resistance was around 964oK /W for the soldered module, and 2.30oK /W for pressure-free sintered module. In summary, pressure-free large-area sintered joints were achieved and passed the fabrication process for IGBT half-bridge module with wiring bonding. Packaged devices with these kinds of joints were verified with good electrical performance. However, thermal performances of pressure-free joints were worse than solder joints and pressure-sintered joints. / Master of Science

This work presents the design and construction of a self-deployable, self-stiffening,and retractable (SDSR) space array from carbon fiber reinforced polymers (CFRP’s) and a working prototype is demonstrated. The effort required developing principles for the design of high-strain composite flexural joints and their integration into angled composite panels. Designing LET arrays in angled panels is explored. Analysis of simple composite LET joints is presented for two degrees of freedom. Validation of the composite LET modeling is sought through numerical methods and empirical testing. Testing of several composite LET joint specimens is conducted and the results are reported. Results indicate that (while not as compact as their isotropic material counterparts) composite laminates can successfully use LET joints as surrogate folds.

This thesis contains several distinct studies aimed at better understanding fracturing in compressional fault-cored folds. At outcrops of growth strata in the Oliana anticline in the Spanish Pyrenees, the relationship of two joint sets may reflect changing mechanical properties (i.e. via diagenesis) during the folding process. Using a Schmidt hammer, I assess the rigidity contrast between the individual units and suggest that late-stage, throughgoing joints formed in strata with conditions similar to those of the present day and that early, bed-contained joints formed when the rigidity contrast between beds was significantly greater than the present day contrast. Modeling algorithms that are used for fracture prediction assume plane strain to construct, model and restore fault-cored folds. Using mechanical models that allow heterogeneous transport in three dimensions, I explore the distribution and magnitude of out-of-plane transport in plunging fault-cored anticlines and provide guidelines of where plane strain should and should not be applied. I show that out-of-plane transport is significant in the simplest non-cylindrical folds, and suggest that complex non-cylindrical structures should not be modeled using plane strain. I mapped five bed-orthogonal fracture sets associated with folding and faulting events at Sant Corneli anticline, a non-cylindrical, fault related anticline in the Spanish Pyrenees. Fold axis perpendicular, calcite healed joint sets associated with similarly oriented normal faulting both pre-date, and are cross cut by calcite healed, N-NW striking joints. Later bed strike oblique joint sets are distinguished by the presence of iron oxide mineralization that probably occurred during Paleocene-Oligocene time. This study directly links fold-related fracturing to fold evolution because fracture sets can be dated relative to the structural evolution of the anticline. I use three-dimensional restorations of Sant Corneli anticline in the Spanish Pyrenees to test the fracture prediction capability of a fully three-dimensional finite element geomechanical restoration algorithm. Reconstruction of the three-dimensional architecture of the syn-tectonic strata provides a template for incrementally unfolding the anticline. Strains predicted by the restorations are compared to the fracture sets that formed over the corresponding time intervals, which are consistent with the observed fracture patterns at Sant Corneli anticline.

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