Plate Segments Research Articles

Analysis of eccentrically stiffened plates with mixed boundary conditions using differential quadrature method

Differential quadrature solution for the flexural analysis of eccentrically stiffened plates subjected to transverse uniform loads is presented. In-plane forces in the plate are considered to take into account the axial stiffness of the plate and the interaction between the beams and the plate due to the eccentricity. Torsional and shear stiffnesses of the beams are also considered. The analysis procedure presented can be used for: point loads applied at the corners of the plate segments; roller point supports at the corners of the plate segments; and outer edges having different combinations of boundary conditions, which includes, free, simply supported, clamped, or resting on beams. The method gives the same accuracy for the moments and shears as that for the deflections and is computationally efficient and simple to program. The results for single panels with complicated boundary conditions are compared with the available exact results. Two examples, one with central eccentric stiffener, and the other with two central mutually perpendicular stiffeners are analyzed and compared with the available results. An example of a plate with no stiffeners but with mixed boundary conditions is also analyzed and compared with the finite element results. All the results are close to the published results.

Vibration of Plates Having Orthogonal Straight Edges with Clamped Boundaries

A domain decomposition procedure is employed to investigate the vibratory characteristics of plates having orthogonal straight edges with fully clamped boundary conditions. Three rectangular segments are used to construct an L-shaped plate element by enforcing continuities along the adjacent segments in displacement, slope, and higher derivatives. The strain and kinetic energies of each plate segment are coupled through the continuity matrices, resulting in a global energy functional for the entire plate domain. A governing eigenvalue equation is derived by minimizing the energy functional by following the Ritz procedure. A set of beam characteristic orthogonal polynomials is employed as the admissible displacement function for each plate segment. By virtue of symmetry in geometry, the basic L-shaped plate element is employed to construct plates of I and cross shapes, and vibration solutions of these plates are obtained via the domain decomposition procedure.

Dose Variation at Bone/Titanium Interfaces Using Titanium Hollow Screw Osseointegrating Reconstruction Plates

Purpose: To evaluate dose variations at bone/titanium interfaces in an experimental model designed to simulate postoperative radiotherapy in patients with mandibular reconstructions using a titanium hollow-screw osseointegrating reconstruction plate (THORP) system. Materials and Methods: The model consisted of a 25 × 25 × 10 mm 3 block of fresh bovine femoral diaphysis, to the surface of which a segment of THORP system reconstruction plate was fixed by means of a solid titanium screw 4 mm in diameter and 10 mm in length. Using specially designed thermoluminescent dosimeters (TLD) 2 mm in diameter and 0.13 mm in thickness, dose measurements were carried out at four distances from the screw axis (0.1, 0.3, 0.6, and 1 mm). 60Co and 6-MV photon beams were used at incidences both perpendicular and parallel (“axial”) to the screw axis. Results: For 6-MV X-ray beams incident perpendicular to the screw axis, the maximum dose enhancement (due to backscatter) and the maximum dose reduction (due to attenuation) at the bone/titanium interface were 5% (± 2%) and 6% (± 2%), respectively. The corresponding values for 60Co beams were 6% (± 5%) and 10% (± 5%). For the axial incidences, a maximum dose enhancement of 5–7% was noted for both 6-MV X-rays and 60Co for beams incident on the surface containing the THORP plate segment, whereas beams incident on the opposite surface induced only a very small dose enhancement (2–3%). Conclusion: Using a new experimental model, TLD measurements showed only marginally significant dose variations at bone/titanium interfaces around THORP screws, all measured values being very close to the uncertainty limits (± 5%) associated with the method. For both 60Co and 6-MV beams, dose variations appeared smaller for axial than for perpendicular incidences. Because photon beams used in head and neck cancer treatment are most often directed parallel to the screw axes, these results suggest that failures of prosthetic osseointegration are unlikely to be explained by an overdosage at the bone/titanium interface.

Transfert de masse sur une plaque finie placée en regard d'une matrice de jets: influence des reprises et de la forme des orifices d'injection

Using a cold hydraulic facility, we determine the convective mass transfer coefficients: local and global, from the surface of a flat plate segment impinging by axisymetrical circular jets coming through inline holes and pipe injectors from a plenum facing the plate. After the impact, the fluid is extracted from the confined space located between the plate and the plenum by means of exhausts whose influence we intend to examine: number and location. We show that transfers are increased by 5% when the extraction occurs by four exhausts and not by only one. As for the exhaust location (height), it clearly appears that the parameter is more significant since the local and global mass transfer increase can reach 15% when we move away the exhausts from the injection plane of the plenum. The comparison of the two configurations, with holes and pipe injectors, points out that the second one has an advantage over the first one which can be materialized by a mass transfer increase of 17%. A dynamic wall study, based on measurements of local friction and fluid direction gives a realistic view of flow structures and allows us to explain in a satisfying way the transfer evolution obtained.

Age, origin and geodynamic significance of plagiogranites in lherzolites and gabbros of the Piedmont-Ligurian ocean basin

U-Pb zircon dating, Sr-Nd isotope tracing and major/trace/RE element analyses were performed to constrain the age, origin and geodynamic significance of plagiogranites that intrude lherzolites and gabbros in the Ligurian Alps and the Northern Apennines. In addition, a host Fe-diorite was investigated. Samples from the Ligurian Alps were collected from the Voltri Group and the Sestri-Voltaggio Zone, whereas the plagiogranites from the Northern Apennines were taken in the Bracco unit. All these units have been affected by Alpine metamorphism reaching eclogite facies in the Voltri Group, blueschist degree in the Sestri Voltaggio samples, and prehnite-pumpellyite facies in the Bracco Unit, which has additionally been affected by rodingitization.U-Pb zircon ages of 150 ± 1, 153 ± 1 and ≈ 156 Ma were obtained, respectively, for two plagiogranites and the host Fe-diorite in the Ligurian Alps, and an age of 153 ± 1 Ma was determined for the plagiogranite in Northern Apennines. Inherited components in zircon and initial Pb in plagioclase indicate mixing of variously differentiated basaltic magmas with small amounts of roughly 1.7–2.1 Ga old continental crust material. REE patterns in both the plagiogranites and the host diorite are characterized by high REE abundance, and moderate LREE enrichment. Nd isotopic compositions lie in the range of N-MORB sources, yielding initial epsilon Nd values between + 8.8 and + 9.7, whereas Sr is isotopically heterogeneous. The geochemical pattern of the plagiogranites and the host Fe-diorite requires melting of a MORB-type mantle source that experienced LREE enrichment shortly before melting. The most likely explanation for such enrichment is the injection of melts derived by small degrees of melting from an adjacent mantle region. The basaltic, LREE-enriched parent magmas generated from this enriched domain have probably undergone up to about 72% of low-pressure fractional crystallization prior to their emplacement into the gabbro-peridotite complex.The 156–150 Ma magmatism occurred in close relation to normal faulting, sedimentation of breccias, and detachment of the mantle complex from its overlying continental crust, followed by exposure on the ocean floor. This tectono-magmatic event in the Ligurian Alps and the Northern Apennines reflects rifting of the Adriatic-Iberian continental plate segment, preceding wider opening of the Piedmont-Ligurian ocean basin and pillow basalt deposition.

Separation failure in a class of bonded plates

Separation failure of bonded elastic plates is considered for a class of mathematically one-dimensional structural configurations under various loading and support conditions. These include configurations simulating those of lap joints and ‘patched’ plates in which intermediate edge debonding occurs as a result of applied in-plane tension, three-point loading, and applied transverse pressure. The problems are approached from a unified point of view, as moving boundary problems in the calculus of variations. In this way a self-consistent mathematical model for the intact segment of the composite structure, for the debonded segments of the composite structure, and for the individual plate segments along with the corresponding boundary and matching conditions are obtained, as well as the transversality conditions which define the moving boundaries of a contact zone and of the bonded region itself. The latter establishes the energy release rates for the debonding structures. Numerical results based on analytical solutions then establish delamination paths or threshold curves which predict the onset and propagation characteristics of the evolving structures. These characteristics are seen to be dependent upon the loading conditions, the support conditions, the relative stiffnesses and lengths of the two primitive plates, and on the initial size of the bonded region.

Natural convection heat transfer in overlapping discrete plate arrays

A numerical solution of the boundary layer equations was obtained using a finite difference formulation for natural convection in an array of vertical overlapping discrete plate segments. The results obtained are presented along with a comparison with the results for a continuous plate array. It was found that the overlapping arrays can enhance the heat transfer rate by as much as 80–90% for fixed values of the wall-to-ambient temperature difference and heat transfer area. The attainment of heat transfer enhancement by the use of discrete plates is possible only in certain ranges of the modified Rayleigh number.

Geologic implications of great interplate earthquakes along the Aleutian Arc

The Aleutian arc is one of the most seismically active regions of the world. It consists of a number of segments or blocks that are rotating clockwise and translating westward along the North American‐Pacific plate boundary. Two of the largest recorded earthquakes have occurred along the interplate boundary south of the Andreanof Islands in 1957 and the Rat Islands in 1965. The large magnitudes of these earthquakes implied that the probability of the recurrence of a large‐magnitude event at these same locations was low. However, the occurrence of a great earthquake south of the Andreanof Islands in 1986 less than 30 years after the 1957 event has prompted a reevaluation of the seismic potential of the arc. We present new marine geophysical observations and synthesize previous geologic interpretations of the Aleutian arc to show that the epicenters of these great thrust‐type earthquakes coincide with upper plate segments of the arc characterized by a coherent forearc structural fabric. These segments, which are associated with large plutonic masses, are mechanically stronger and are related to the location of asperities positioned at depth along the main thrust zone; they appear to be more strongly attached to the North American plate than adjacent blocks. The tectonically controlled locations of these asperities thus appear to influence the seismicity along the arc. The Andreanof and Rat segments of the arc are separated by the Delarof segment, which is considered to have a high probability of a large‐magnitude earthquake in the near future based on probabilistic estimates of seismic potential (Nishenko, 1991). The Delarof segment of the arc, however, is highly disrupted by arc‐transverse faults. This segment is structurally weak and does not appear to be capable of accumulating the interplate strain necessary to generate a great, subduction zone earthquake. We propose that variations in upper plate structural strength and mobility affect the mechanical properties of the interplate thrust zone and need to be considered in localizing interplate asperities. Forearc tectonic segmentation associated with the partitioning of strike‐slip and thrust motions may exert long‐term controls on the rates of seismic moment release.

Method of manufacturing a curved array ultrasonic transducer assembly

A curved array ultrasonic transducer is manufactured by cutting a flat transducer plate, which is attached to a flexible support plate, into a plurality of segments, the segments being hingedly attached by the support plate. The support plate is bent to a radius and the conductive traces in a flexible circuit board are electrically connected to the transducer plate segments. The flexible circuit board, having a plurality of branches, is bent to a perpendicular position such that the traces in the plurality of branches become substantially aligned. The traces exiting the branches are then electrically connected to a pin and socket connector device.

Structural modeling of composite beams with induced-strain actuators

This paper presents an analytical-experimental investigation on structural modeling of coupled composite beams with distributed induced-strain actuators. Analysis based on Vlasov theory is developed to include distributed piezoelectric actuators, either surface mounted or embedded. Salient features of composite open-section beam analysis, like constrained warping and transverse shear deformation, were included. Induced-strain actuation was introduced in the constitutive relations of plate segment of the open-section composite beams. To evaluate the analytical predictions, several bending-torsion and extension-torsion coupled graphite-epoxy solid beams were fabricated using an autoclave molding technique. These were surface mounted with piezoelectric actuators. The actuators were excited to produce local bending moment and axial force on the beam, and the structural response was measured in terms of bending slope, induced twist, and surface strain. Good correlation between analysis and experiment was achieved. Because of the existence of a chordwise actuator moment, the induced twist of bending-torsi on coupled beams was significantly influenced by including the chordwise curvature of the plate segment of beam in the formulation. For [45]i4 solid beams, the chordwise bending of the plate segment of beam was found to increase the tip twist by about

Heat transfer in the boundary layer of a ‘gas-evaporating drops’ two-phase mixture

A mist flow in a laminar boundary layer over a hot flat plate is studied by asymptotic and numerical methods. A two-continuum approximation is used to describe the ‘gas-evaporating drops’ twophase medium. The Saffman force, acting on the drops and causing their deposition, is taken into account. The mechanism of heat transfer enhancement by the drops evaporating in the boundary layer has been studied, and similarity criteria have been found. The predicted overall heat transfer coefficient for a plate segment is in good agreement with the familiar experimental data.

Magnetostratigraphic Constraints on the Development of Paired Fold-Thrust Belts/Foreland Basins in the Argentine Andes

Development of a paired fold thrust-thrust belt/foreland basin is correlated to the flattening of the subducting Nazca plate between 28-33{degree}S. Magnetostratigraphic studies in neogene basin-filling continental strata determine local basin subsidence rates and provide relatively precise chronostratigraphic correlation between different depositional environments. The data demonstrate that most existing lithostratigraphic units are diachronous and require new tectonic interpretations. Increases in sediment accumulation rates closely correspond to changes in provenance and indicate that the Frontal Cordillera, on the Chile-Argentina border was a positive topographic province by 18 Ma. The Precordillera evolved from {approx}16 Ma to the present as thrusting migrated from west to east. Published ages from intercalated airfall tuffs constrain some sedimentary sections in the eastern Sierras Pampeanas where the earliest uplift occurred since 10 Ma. The youngest uplifts are on the west side close to continuing thrusting in the Precordillera. Not all fold-thrust belt/foreland basin pairs are associated with flat subduction, suggesting that tectonic controls exceeding the scale of individual plate segments may be important. The hydrocarbon-producing Subandean fold-thrust belt/foreland basin, located in the area of 'steep' subduction that underlies northern Argentina and Bolivia (18-24{degree}S), is also believed to have evolved since middle Miocene time. Recently initiated magnetostratigraphic studies inmore » the Subandean foreland basin will attempt to temporally constrain the Neogene tectonic evolution for comparison with the southern region.« less

Membrane action in the beam mechanism

Bending moment and axial force interaction formulae are derived for a fully plastic section comprising up to three plate segments. They are utilized in a plastic mechanism analysis of a point-loaded beam with partial axial restraint. The destabilizing effect of a pre-compression stress is noted. The range of validity of the analysis is limited by material tearing at large strains, and so the manner in which the strain increases with lateral deflection, and its dependence on the beam geometry and the precise length over which the load is applied, are studied. Tests and finite element solutions are described, which show good agreement with the mechanism approach.

Interactive buckling in thin-walled beams—I. Theory

A method is derived for the analysis of mode interaction in thin-walled elastic beams. A nonlinear plate theory is employed for the plate segments of the beam, in which the exact nonlinear expressions are used for the middle surface strain measures, but the bending measures are linearized. The beam is subjected to a combination of axial compression and a constant bending moment, and it is assumed to be simply supported at the ends. In the calculation of the total potential energy, the influence of the prebuckling deformations is neglected. The finite strip method is used with the transverse variation of all three displacement components described by cubic polynomials in the arc length. The nonlinear mode interaction is analysed by means of Koiter's asymptotic theory of stability. Some applications of the method to representative problems are presented in a subsequent paper by the authors. This shows that significant mode interaction and imperfection sensitivity occur in these structures.

A study of eddy-current effects in the structure of the westinghouse LCT coil

One of the six 2.5- × 3.5-m-bore 8-T superconducting magnets of the international Large Coil Task (LCT) was designed and fabricated by Westinghouse Electric Corporation with the oversight of Oak Ridge National Laboratory. This coil, designated WH, has a mechanical structure composed of a stack of aluminum plate segments held together with stainless throughbolts. When the magnetic flux through the coil is changed, voltage is induced in the structure, and to avoid excessive currents the design provided low-voltage insulation between plate segments. However, during construction it appeared that this anodizing layer may have been breached extensively. Electrical tests on delivery confirmed this, and supplemental instrumentation was added to the structure before the coil was installed in the test facility. The shorting raised concerns about increased refrigeration load, local overheating, and a change in dump characteristics. After installation, current ramps to 5 A showed magnetic diffusion time constants of 1.5 s at room temperature and 3.0 s at 20 K, an order of magnitude larger than for the other LCT coils. These latter coils have structural cases of stainless steel, which has an electrical resistivity 17 times that of the 2219-T87 aluminum used in the WH coil. In tests at operating currents, temporal values of voltage, current, temperature, and energy distribution during ramp and dump agree with those values calculated on the basis that the aluminum structure is solid, and are quite different from values calculated without considering shorting. On dump, the coil is partially self-protecting, but 23% of the initial stored energy is deposited in the structure at cryogenic temperature. The various effects of the shorting are apparently tolerable for testing in the International Fusion Superconducting Magnet Test Facility (IFSMTF). For other cases, the coil designer should carefully consider if and how the structure should be electrically segmented.

Stress in the Indo-Australian plate

Cloetingh, S. and Wortel, R., 1986. Stress in the Ind~Austr~ian plate. In: B. Johnson and A.W. Bally (Editors), Intraplate Deformation: Characteristics, Processes and Causes. Tectonophysics, 132: 49-67 We modelled the state of stress in the Indo-Australian plate in order to investigate quantitatively variations observed in tectonic style. The numerical procedure incorporates the dependence of slab pull and ridge push on the age of the oceanic lithosphere. Estimates are presented for the average net resistive forces at the Himalayan collision zone, the suction force acting on the overriding Indo-Australian plate segment at the Tonga-Kermadec trench and the drag at the base of the lithosphere. Our modelhng shows a concen~ation of compressive stresses of the order of 3-5 lcbar in the Ninetyeast Ridge area; the effects of the compressive resistance associated with Himalayan collision and subduction of young lithosphere off the northern part of the Sunda arc are focused in this region. The stress field as calculated gives a consistent explanation for the observed concentration of seismic activity (Stein and Okal, 1978) and significant deformation in the oceanic crust (Weissel et al., 1980; McAdoo and Sandwell, 1985) in the area. The calculated stress field in the area adjacent to the Southeast and Central India ridges is characterized by tension parallel to the spreading axis. This explains the concentration of near-ridge normal faulting seismicity (with T-axes subparaIle1 to the spreading ridge) in the Indian Ocean as recently observed by Bergman et al. (1984) and Wiens and Stein (1984). The regional stress field along the strike of the Sunda arc varies from compression seaward of and parallel to the Sumatra trench segment, to tension perpendicular to the Java-Flores segment. This explains the selective occurrence of well developed grabens seaward off the Java-Flores segment of the trench, observed by Hilde (1983). Our modelling shows that the observed rotation of the stress field (Denham et al., 1979) in the Australian continent is mainly the consequence of its geographic position relative to the surrounding trench segments and the variations of the forces acting on the down-going slab in each of these. The state of compression in west and central Australia is induced by the action of resistive forces at the Himalayan and Banda arc collision zones. The joint occurrence of high levels of compression in the plate’s interior and normal faulting seismicity in the near-ridge areas, is a transient feature unique to the present dynamic situation of the Indo-Australian plate.

EFFECTS OF PRE-BUCKLING DEFLECTIONS ON LOCAL, DISTORTIONAL AND LATERAL-TORSIONAL BUCKLING OF I-BEAMS

The displacement and strain distributions for a plate segment comprising open cross section are derived considering the pre-buckling deflection of beam axis. Applying the higher order theory obtained to I-beams bent about their major axes by equal end moments, the effects of pre-buckling deflections on local, distortional and lateral-torsional buckling are investigated. Solving eigen-value problems, it is clarified that the stress corresponding to distortional buckle of an I-beam is conservative compared with that neglecting the pre-buckling deflections and the stress corresponding to lateral-torsional buckle occuring at long lengths are progressive compared with the results of Timoshenko.

Geometry of the subducted plate near Kodiak Island and Lower Cook Inlet, Alaska, determined from relocated earthquake hypocenters

Abstract Using observations from 28 seismograph stations in southern Alaska, we have used the JHD method to relocate 341 well-recorded events with focal depths beneath about 40 km which occurred between 56.4°N and 60.5°N, and between 151.6°W and 156.5°W. These hypocenters show that the Wadati-Benioff zone has a dip of about 45°. However, its strike changes by about 15° beneath Lower Cook Inlet at about 59°N near where the volcanic line also bends northward. Near this bend there is also a distinctly higher level of seismic activity than in the area to the southwest of 59°N. A few events are situated about 20 km beneath the main Wadati-Benioff zone in Cook Inlet, and a focal mechanism we have determined for one of these differs from other mechanisms for events in this area. Focal mechanisms available from previous work show that at intermediate focal depths the area between 59°N and 60.5°N is controlled by horizontal north-south compression, and as such differs from the region to the southwest. Relying primarily on the observed change in strike and apparent thickness of the Wadati-Benioff zone, we interpret these data to suggest that the subducted lithophere separates into two distinct segments as it subducts beneath Cook Inlet. Because the direction of subduction is not perpendicular to the volcanic arc, the events situated beneath the Wadati-Benioff zone in Cook Inlet may be part of the southwestern plate segment. Although the geometry and available focal mechanisms for events beneath Cook Inlet are similar to what would be expected in a “double Wadati-Benioff zone,” we suggest instead that these observations result because we are at the boundary between two adjacent segments of the subducting plate.

Geological setting of hydrothermal activity at 12°50′N on the East Pacific Rise: A submersible study

A detailed submersible investigation of a 20-km segment of the East Pacific Rise near 12°50′N between the Orozco and Clipperton fracture zones has resulted in the localization of 24 active hydrothermal vent fields and over 80 sites of sulfide accumulations. The active vents range from low-temperature vents characterized by exotic benthic communities to high-temperature “black smokers” and the deposition of polymetallic sulfides. The study is based upon a combination of fine scale topography obtained using the SEABEAM sonar system on N/O “Jean Charcot”, camera lowerings along the axis using the RAIE vehicle, and 32 dives by the submersible “Cyana” operating from N/O “Le Suroit”. The observations made between the Orozco and Clipperton fracture zones show topographic highs situated along the strike of the accreting plate segment separated by a small ridge offset at 11°49′N. This offset divides this portion of the ridge into two separate spreading segments each of which has a primary topographic high along strike. Secondary highs are associated with each segment of the ridge separated by either small offsets (or relay zones) or in some cases, zones where spreading centers overlap. Dives made on the tops of both primary highs (12°50′N and 11°30′N) confirm the presence inferred from previous surface work of high-temperature vent fields while one reconnaissance dive (14°20′N) near the Orozco fracture zone/ridge axis intersection reveals the absence of any hydrothermal activity in the present or recent past. The vast majority of vent fields investigated were found at the topographic high near 12°50′N, are associated with the most recent period of volcanism, and are confined to lava ponds situated within the axial graben.

Western Irian Jaya: The end-product of oblique plate convergence in the late tertiary

The island of New Guinea is the surface expression of the deformed northern margin of the Australian continental block: to the south undeformed continental crust is overlain by flat-lying platform sediments that form a conformable sequence from late Palaeozoic to late Tertiary. Along the New Guinea Cordillera these platform sediments have been tightly folded and overthrust to the south as a result of crustal shortening caused by convergence between the Australian Plate and the Pacific Plate. The earth movements resulting from this convergence started at the end of the Miocene and continue to the present day. It is postulated that all the major structures of western Irian Jaya were caused by this orogeny and can be explained by the convergence directed southwest-northeast, between the Australian and Pacific plates. It is further postulated that the convergence has remained essentially constant since the start of the earth movements. This convergence is consistent with that postulated in the Circum-Pacific Plate Tectonic Map (AAPG, 1981) of 12.5 cm/yr directed about 15° south of west, only if the effects of the Sorong-Yapen fault system are taken into account. This complex, east-west-trending fault system forms the southern boundary of the Pacific Plate and has responded to the convergence by left-lateral strike-slip displacement of at least 370 km since the late Miocene. As a consequence, south of the Sorong-Yapen fault system the convergence has been directed more to the south i.e. at least 45° south of west. In this region south of the fault zones, the north-south component of the convergence has been accommodated in the east by folding and overthrusting over a wide zone of interaction called the New Guinea Mobile Belt (Dow, 1977). In the west on the other hand, the Australian continental crust has been a stable buttress (Kepala Burung, Fig. 2) which, following convergence, has protruded into the Pacific Plate. Its northeastern margin has therefore been exposed to the full brunt of collision with the Pacific Plate and large segments of continental crust have been broken off and rafted westwards. In order to accommodate the difference in crustal shortening between the New Guinea Mobile Belt and Kepala Burung, two fundamental crustal fractures formed in the intervening region: the Waipoga and Wandamen faults. These fractures make angles of about 65° with the regional structural trend (Fig. 2) and they were the focus of most of the resulting differential crustal displacement. Two of the more spectacular examples of this differential movement have been the thrusting of large slabs of crustal rocks tens of kilometres southwards over the Australian continental crust (Weyland Overthrust and Lengguru Fold Belt).