Dead Weight Loading Research Articles

On-site and Laboratory Investigation of Materials and Structure of a Belltower in Monza / Untersuchungen an den Werkstoffen und am Tragwerk im Labor und am Objekt am Beispiel eines Glockenturms in Monza

Abstract After the collapse of some heavy buildings and towers in Italy and elsewhere, the hypothesis of possible continuous damage to these structures due to the dead weight and cyclic loads (wind, temperature variations, etc.) has been formulated by the authors. The long term behaviour of historic masonry has also been detected by laboratory creep and cyclic tests. The results indicate that a laboratory and on site investigation together with analytical modelling are important particularly for tall bell-towers. The application of these procedures on the Bell-Tower of the Cathedral of Monza is here reported and discussed

Estimate of the Effect of the Dead Weight Load of Rocks on Their Deformation near Workings

The deformation of a rock mass modeled by a half-plane weakened by a circular opening is investigated with allowance for gravity forces. An integral relation is established between all components of the stresses and displacements on the boundary of the region under consideration; this makes it possible to solve inverse and overdetermined problems of geomechanics.

Evaluation of Advanced Solid Lubricant Coatings for Foil Air Bearings Operating at 25° and 500°C

The tribological properties of one chrome oxide and one chrome carbide based solid lubricant coating were evaluated in a partial-arc foil bearing at 25° and 500°C. Start/stop bearing operation up to 20,000 cycles were run under 10 kPa (1.5 psi) static deadweight load. Bearing friction (torque) was measured during the test. Specimen wear and SEM/EDS surface analyses were conducted after testing to understand and elucidate the tribological characteristics observed. The chrome oxide coating which contains both Ag and BaF2/CaF2for low and high temperature lubrication, exhibited low friction in sliding against Al2O3 coated foils at 25° and 500°C. The chrome carbide coating, which lacked a low temperature lubricant but contained BaF2/CaF2 as a high temperature lubricant, exhibited high friction at 25°C and low friction at 500°C against both bare and Al2O3 coated superalloy foil surfaces. Post test surface analyses suggest that improved tribological performance is exhibited when a lubricant film from the coating transfers to the foil surface. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in Toronto, Ontario, Canada, October 26–28, 1998

Elliptical flexure hinges

This paper presents closed form equations based on a modification of those originally derived by Paros and Weisbord in 1965, for the mechanical compliance of a simple monolithic flexure hinge of elliptic cross section, the geometry of which is determined by the ratio ε of the major and minor axes. It is shown that these equations converge at ε=1 to the Paros and Weisbord equations for a hinge of circular section and at ε ⇒∞ to the equations predicted from simple beam bending theory for the compliance of a cantilever beam. These equations are then assessed by comparison with results from finite element analysis over a range of geometries typical of many hinge designs. Based on the finite element analysis, stress concentration factors for the elliptical hinge are also presented. As a further verification of these equations, a number of elliptical hinges were manufactured on a CNC milling machine. Experimental data were produced by applying a bending moment using dead weight loading and measuring subsequent angular deflections with a laser interferometer. In general, it was found that predictions for the compliance of elliptical hinges are likely to be within 12% for a range of geometries with the ratio βx (=t/2ax) between 0.06 and 0.2 and for values of ε between 1 and 10.

Increasing the accuracy and efficiency of a conveyor balance

A fundamentally new comprehensive conveyor balance design is proposed along with an indirect method of calibration by deadweight loading. Calculated and experimental estimates of the metrological characteristics are given.

Innovative liner support trials in underground hardrock mines: S. Espley, C. Langille & D. McCreath, CIM Bulletin, 88(922), 1995, pp 66–74

In 1993, trials of two innovative applications of liner support involving the replacement of bolts in the ground support system were undertaken at Inco mines. The first trial involved an evaluation of the effect of dynamic loading on mesh-reinforced boltless shotcrete in a sub-level cave mining area on 2400 level at Stobie Mine. The second trial involved an evaluation of the MIROC Mineguard spray-on liner as a replacement for bolts and screen support, or as a replacement for screen support alone, in a topsoil heading of a bulk, VRM (vertical retreat mining) stope on 3240 level at Lower Coleman Mine. In the Stobie Mine trial, an uppers retreat heading was supported using a two-pass system. Fist, shotcrete was applied 2 inches thick, following by pinning of mesh screen to the back and walls. A second pass of another 2 inches of shotcrete was then performed. For recovery of the ore zone, a vertical slot was created using a Borepak blind boring machine. The uppers rings were blasted, one or two rings at a time, starting at the slot and retreating out of the heading. During blasting of the production rings, blast monitoring was used to record the ppvs (peak particle velocities). For a serie of 5-ring blasts, the maximum ppvs were measured to be 0.4 m/s (16 in./s) with a maximum charge weight per dely of 357 kg (800 lb). Six 5-point convergence measurement stations were set up and after each blast the total rockmass convergence was measured using a tape extensometer. Although a maximum displacement of 100 (4 in.) was measured, the shotcrete still managed to provide some support function. A support damage assessment was also done to try and relate blast vibration of effectiveness of the mesh reinforced shotcrete liner. This trial demonstrated the effect that blasting has, on a support system, and it also demonstrated the necessity of having the mesh reinforcement properly placed within the shotcrete. The Lower Coleman Mine trial involved the development of an engineered design to create a dead-weight loading system to test the standard rockbolts and screen support system versus a polyurethane liner support system, with and without the installation of rock bolts. Each support was evaluated on its ability to support a dead-weight load or a slab of rock having dimensions 12 ft by 20 ft by 4 ft thick. A development and blasting scenario was designed and implemented for the creation of the dead-weight load in the topsill heading. Initially the heading was driven developed 20 ft high and 20 ft wide and then it was advanced another 100 ft using a reduced back height of 15 ft. This created a 5 ft hanging breast, support system. For each test, the brow was drilled off with closely spaced horizontl perimeter holes, each being 12 ft in length and with a 4 ft burden. Additional horizontal perimeter holes were drilled along the shoulders of the brow area to within 1 ft of the back. Further down the drift from the brow, closely spaced up-holes were drilled, each 5 ft in length, to intersect the toe-locations of the horizontal perimeter holes.

Loading configurations and driving mechanisms for joints based on the Griffith energy-balance concept

Using the Griffith energy-balance concept to model joint propagation in the brittle crust, two laboratory loading configurations serve as appropriate analogs for in situ conditions: the dead-weight load and the fixed-grips load. The distinction between these loading configurations is based largely on whether or not a loaded boundary moves as a joint grows. During displacement of a loaded boundary, the energy necessary for joint propagation comes from work by the dead weight (i.e., a remote stress). When the loaded boundary remains stationary, as if held by rigid grips, the energy for joint propagation develops upon release of elastic strain energy within the rock mass. These two generic loading configurations serve as models for four common natural loading configurations: a joint-normal load; a thermoelastic load; a fluid load; and an axial load. Each loading configuration triggers a different joint-driving mechanism, each of which is the release of energy through elastic strain and/or work. The four mechanisms for energy release are joint-normal stretching, elastic contraction, poroelastic contraction under either a constant fluid drive or fluid decompression, and axial shortening, respectively.Geological circumstances favoring each of the joint-driving mechanisms are as follows. The release of work under joint-normal stretching occurs whenever layer-parallel extension keeps pace with slow or subcritical joint propagation. Under fixed grips, a substantial crack-normal tensile stress can accumulate by thermoelastic contraction until joint propagation is driven by the release of elastic strain energy. Within the Earth the rate of joint propagation dictates which of these two driving mechanisms operates, with faster propagation driven by release of strain energy. Like a dead-weight load acting to separate the joint walls, pore fluid exerts a traction on the interior of some joints. Joint propagation under fluid loading may be driven by a release of elastic strain energy and/or work by the pore fluid during poroelastic contraction. Again, propagation velocity dictates the driving mechanism, with critical to supercritical joint propagation accompanying fluid decompression and subcritical crack propagation taking place under a constant fluid drive. During axial shortening a jointing process called axial splitting may occur following wing crack growth from an initial crack tilted relative to the maximum compressive stress. Here the joint-driving mechanism may be either the work of a remote stress (i.e., a dead weight) or the release of elastic strain energy (i.e., fixed grips).

A Study on Wire Sweep in Encapsulation of Semiconductor Chips Using Simulated Experiments

An effort has been made in this study to develop a model which can predict wire sweep during semiconductor chip encapsulation with transfer molding. The calculation of wire sweep during encapsulation depends on many factors. In this study, a step-by-step approach has been used considering one factor at a time. As the first step, the wire deformation has been measured and calculated under a known dead-weight loading. The next step has been to measure and calculate the deformation of a single straight wire attached to the mid-plane of a rectangular cavity due to the flow of a clear and homogeneous fluid. Finally, the wire deformation due to the flow has been measured and calculated when a wire of general shape is attached to a leadframe. The effect of bubble on the wire-sweep has been analyzed qualitatively. Through this series of experiments, a first step in the development of model for the prediction of wire sweep during chip encapsulation has been made.

Wear at microscopic scales and light loads for MEMS applications

The fabrication of micro electro mechanical systems (MEMS) such as micromotors is mainly based on silicon and its compounds and their tribological behaviour plays a key role in the performance of such systems. In this paper the wear of MEMS-compatible materials has been investigated for a range of contact areas and contact forces typical of micro electro mechanical systems. Special test specimens incorporating a range of micromachined micro structures on their top surfaces were fabricated in order to simulate those conditions. The micro structures were coated with diamond-like carbon (DLC), silicon nitride, silicon dioxide, and doped polysilicon. A specimen-on-disc arrangement was used for the wear experiments and dead weight loading was applied. The results show that the wear rate of DLC and single-crystal silicon sliding on DLC decreases with increasing sliding distance whereas silicon dioxide and silicon nitride showed linear wear behaviour. The effect of contact morphology and contact pressure was investigated for doped polysilicon sliding on DLC. The results can be attributed to the differing mechanical and chemical properties of the materials leading to wear mechanisms ranging from asperity fracture to asperity deformation.

Surface friction effects related to pressforming of continuous fibre thermoplastic composites

Abstract In the pressforming of thermoplastic composite sheet, the heated laminate is rapidly formed into a mould. The moulding force is transmitted using either matched metal dies or by a rubber pad/metal mould combination. Friction must occur between the metal or rubber mould surface and the heated composite as the laminate moves across the tool surface until it is fully formed. This paper describes work carried out to characterize and measure these frictional forces. Composites such as unidirectional carbon fibre-reinforced poly(ether ether ketone) and glass fibre fabric-reinforced PA-12 have been tested, with rubber and tool steel as the mould materials. Two methods of testing were used, one comprising two fixed heated platens, between which the surfaces to be tested were placed while the composite was sheared from between the surfaces. Pulling-out force was achieved using a variable velocity shearing rig and by using dead-weight loading. A heated friction sled was also built which allowed various samples of metal and rubber material to be dragged across a heated composite sheet. The effects of varying surface temperature, normal pressure, surface fibre orientation and mould release agent were investigated. An adhesive bond was found to occur if the surfaces were left in contact during heating. By varying the shearing velocity, the friction between the composite and tool surface was found to be hydrodynamic in nature, i.e. velocity-dependent, at forming temperature.

Collapse of continuous fibre composite beams at elevated temperatures

Short beam tests were performed on continuous graphite fibre/thermoplastic matrix composites between 20 and 300°C. At low temperatures collapse and fracture of the beam is initiated by interlaminar shear and delamination. At high temperatures large-scale inelastic deformation was observed, similar to the deformation of an ideal fibre-reinforced material (IFRM) previously described by Spencer, Pipkin and Rogers and co-workers. With dead-weight loading at loads below the collapse load, creep is observed, also involving IFRM-type deformation, leading to time-dependent collapse of the beam.

A study of wear on MEMS contact morphologies

The fabrication of many micro electro mechanical systems (MEMS) is mainly based on silicon and its compounds and, for moving structures such as micromotors, tribological behaviour plays a key role in the performance. In this paper the wear of MEMS-compatible materials has been investigated for a range of contact areas and contact forces typical of MEMS. Special test specimens incorporating a range of micromachined micro structures on their top surfaces have been fabricated in order to simulate those conditions. These single crystal silicon (SCS) micro structures were coated with a range of materials used in MEMS; diamond-like carbon (DLC), silicon nitride (Si3N4), silicon dioxide (SiO2), and doped and undoped polysilicon. A specimen-on-disc arrangement (a development of the macroscopic pin-on-disc) was used for the wear experiments and dead weight loading was applied using micro loads specially calibrated for this purpose. The results show that the wear rates of DLC and SCS sliding on DLC decrease with increasing sliding distance whereas Si3N4 and SiO2 showed approximately linear wear behaviour. The effect of contact morphology and contact pressure was investigated for doped polysilicon sliding on DLC and for doped and undoped polysilicon sliding on Si3N4. The results can be attributed to the differing mechanical and chemical properties of the materials leading to wear mechanisms ranging from asperity fracture to asperity deformation.

Finite Element Assessment of Thin Shell Structures

A geometrically and physically nonlinear finite element model for thin reinforced concrete shells is presented which allows simulation of the deformation history of imperfect structures up to their numerical failure. Application to the assessment of existing natural draught cooling tower shells subjected to dead weight and wind loading demonstrates the usefulness of the numerical procedure. Results showed that failure was due to a nonlinear stress problem, rather than elastic buckling. For worst-case imperfections relating to the physically nonlinear failure mode, the shells exhibited only a moderate imperfection sensitivity. Further work will concentrate on more realistic imperfection patterns, since worst-case imperfections give a rather too conservative lower bound for the collapse loads.

Large strain analysis of rubber-like membranes under dead weight, gas pressure, and hydrostatic loading

The title problem is formulated variationally. Especially membranes being totally or partly under hydrostatic loading are considered and it is assumed that either the liquid volume or the liquid level is constant during the deformation. The most general case is characterized by an isoperimetric variational problem and free boundaries of the loaded (wetted) surface. Particularly we analyse membrane strips, membranes of revolution, and arbitrary spatial membranes consisting of piecewise plane ones. Numerous numerical results are reported and discussed with respect to the stability of equilibrium. Contact problems are addressed also.

Plastic deformation burst and arrest phenomena in rapidly heated inconel “X” under dead weight loading

Plastic deformation burst and arrest phenomena in rapidly heated inconel “X” under dead weight loading

Development of a Wear Test Apparatus for Screening Bearing-Flange Materials in Computer Tape Drives

An accelerated-wear test apparatus was developed to screen bearing-flange materials. During the test, tape edges rub against two flat test specimens (which are easy to fabricate). The clamping arrangement of the specimens provides the same contact with the tape during repeated tests. The tape is loaded against the sample by deadweight loading, which ensures constant loading, irrespective of tape guiding. Acceleration in wear is obtained by increasing the load at the interface of the tape and the test specimen. Wear tests were conducted on several metals, ceramics and cermets, coatings, and surface treatments. We find that ceramics and cermets have the lowest wear.

Abrasive wear resistance of boron alloyed austenitic Fe—Mn—C‐steels

Alloying additions of 0.25–1.0 wt‐% B to austenitic manganese steels lead to the formation of carboborides arranged in a cell‐type microstructure. Pin abrasion tests on flint grinding paper using different dead weight loads reveal that these carboborides do not substantially improve the wear resistance due to a relatively low hardness and weak bonding to the austenite matrix. However, carboborides hardened by V, e.g., can considerably increase the abrasive wear resistance. They are very effective in a metastable austenitic matrix in which friction‐induced martensitic transformation occurs. It is the consequence of compressive stresses in the martensitic surface layer which improve the anchoring of insufficiently bonded carboborides in the matrix.

The wear rate of n-type Si(100)

Single-crystal Si(100) (n type) was scratched at room temperature by a single-point 90° pyramidal diamond in each of the following fluids: reagent-grade absolute ethanol, methanol, acetone and deionized water. The wear rate in each case was determined from a measurement of the cross-sectional areas of circular multiscratch grooves and the increase in this area with scratching time. These areas vary as the contact force on the diamond and the fluid covering the silicon surface during the scratching test vary. As expected, the wear rate depended on the force (dead-weight load) on the diamond (the wear rate increased as the force was increased) but fluids also had a significant effect on the wear. The wear rate of silicon scratched in ethanol is twice that in deionized water when the dead-weight load on the diamond is 0.49 N and all other experimental variables are held constant. These results were compared with two models of abrasive wear of ceramic materials.

Yield surfaces and loading surfaces of aluminum and brass: An experimental investigation at room and elevated temperatures

This paper presents the results of an experimental investigation with two specimes of commercially pure aluminum and one specimen of free cutting brass. These three experiments under deadweight loading involved the determination of yield surfaces at room and elevated temperatures and the comparison of these yield surfaces with their associated loading surfaces. The prestressings were performed at room and at elevated temperatures; they were three-dimensional and two-dimensional and they included portions directed towards the origin and away from the origin.

Buckling of Thin Walled Beams Under Water Loading

An approximate analysis of end supported, thin‐walled prismatic members of open profile section to predict buckling loads under dead weight and water loading is presented. When the critical buckling mode involves considerable torsional component, the water loading may lead to a significant reduction in the buckling load due to the shift of the centroid of the water weight with respect to the undeformed configuration. A finite element displacement model has been adopted to formulate the discrete critical equilibrium equations. Numerical examples show considerable reductions in critical loads for the water loading case.