Lower Platen Research Articles

The Effects of Loading Conditions on the Behaviour of Fixed-Ended Plain Channel Columns.

The compressive behaviour of column members can be considerably affected by local buckling, material yielding and local end conditions. In this paper, the effects of the loading conditions at the ends of plain channel section columns subjected to uniformly compressed loading, and fixed conditions at the column ends with respect to global rotations, was examined. Finite element simulation was employed to look at the post-buckled response of thin-walled, plain channel section columns that covered the complete loading history of the compression columns from the onset of elastic local buckling through the nonlinear elastic and elastoplastic post-buckling phases of behaviour to final collapse and unloading. Two types of loading conditions were considered: the first was one that has been used practically in tests whereby one end is loaded with a moving top platen while the other end is fixed at the lower platen, but, for the second loading condition, both ends were loaded with equally moving top and lower platens. These two conditions were shown to lead to quite different characteristic interactive responses of the columns due to mode jumping in the buckling mode for the locally rotationally constrained case.

Development of a High Precision Method to Characterize Poisson’s Ratios of Encapsulant Gels Using a Flat Disk Configuration

A high precision test method based on the compression of thin elastomeric disks was developed and implemented in order to measure Poisson’s ratios of a silicone gel and organic gel. Test fixtures consisted of a thin disk of the elastomeric gel cast between two rigid platens with the lower platen containing a centrally installed pressure sensor. A compressive load was applied to the upper glass plate and the resulting stress through the deformed disk was measured using the attached pressure sensor. Poisson’s ratios of the gels were easily determined from the thin disk’s aspect ratio and the ratio of the measured stress from the pressure sensor to the applied compressive stress. The high degree of precision for this technique is indicated by the measured Poisson’s ratios for both materials which were obtained to at least the third significant digit. Additionally, an increase in the precision of this method was observed for lower aspect ratios of the cured disks, specifically the thickness to radius. An alternative high precision cylindrical experimental technique was implemented in this study to compare the resulting Poisson’s ratio measurements to this flat disk method. This method utilized a hollow steel cylinder fitted with matching pairs of pressure sensors located at the top and bottom. Comparable results were found between the two methods for the investigated silicone gel system.

Development of a Bioreactor for Axially Loaded Intervertebral Disc Organ Culture

Whole disc organ culture is needed for preclinical testing of biological repair of the degenerate intervertebral disc. Such organ culture is hampered by two major limitations: first obtaining adequate nutrition though the calcified cartilage endplates adjacent to the vertebral bone, and second by loss of tissue integrity if the endplates are removed from the discs. In this work we utilize a recently described technique for whole disc isolation that overcomes these problems, by removal of vertebral bone and the adjacent calcified portion of the endplate, and the construction of a bioreactor that permits long-term viability of these discs in loaded organ culture. The bioreactor consists of a culture chamber in which the disc can be dynamically loaded in a uniform manner. The culture chamber is large enough to accommodate discs up to 60 mm in diameter, and so is amendable to study both bovine and human discs. The discs are loaded in the culture chamber by upper and lower platens, which conform to the shape of the remaining cartilaginous endplate and permit fluid flow across its surface. The bioreactor is able to load the disc under a variety of conditions ranging from static to dynamic and from physiological to pathological, and monitor induced changes in disc height. To date, bovine caudal discs have been maintained viable in the bioreactor for up to 4 weeks without any appreciable loss of disc height under physiological cyclic load and, in principle, could be maintained in such a manner for several months. Such long-term organ culture is essential for studying biological repair of the disc.

Parametric Study on the Response of Stable Unbonded-Fiber Reinforced Elastomeric Isolators (SU-FREIs)

Tests on stable unbonded (SU) square carbon fiber-reinforced elastomeric isolator (FREI) bearings were conducted to investigate their lateral and vertical response. The bearings are intended for seismic isolation of low-rise buildings including those of ordinary importance. To simulate the in-place application of SU-FREI bearings, the contact surfaces of the bearings were not bonded to the platens of the test machine. This unbonded application permitted stable rollover deformation to occur which enhances the bearing's isolation efficiency. The bearings were shown to safely sustain large lateral displacements. When subjected to large lateral displacements, their originally vertical faces completely contacted the horizontal surfaces of the upper and lower platens, which created a stiffening response and ensured the stability of these very large displacements. The sensitivity of SU-FREI bearings to lateral displacement history and vertical pressure applied on the bearings were investigated. Regarding the latter parameter, it was found that the effect of variations in vertical pressure on the lateral response can be neglected when the SU-FREI bearings are subjected to relatively light vertical pressures such as considered for low-rise buildings.

Parametric Study on the Response of Stable Unbonded Fiber Reinforced Elastomeric Isolators (SU-FREIs)

Tests on stable unbonded (SU) square carbon fiber-reinforced elastomeric isolator (FREI) bearings were conducted to investigate their lateral and vertical response. The bearings are intended for seismic isolation of low-rise buildings including those of ordinary importance. To simulate the in-place application of SU-FREI bearings, the contact surfaces of the bearings were not bonded to the platens of the test machine. This unbonded application permitted stable rollover deformation to occur which enhances the bearing's isolation efficiency. The bearings were shown to safely sustain large lateral displacements. When subjected to large lateral displacements, their originally vertical faces completely contacted the horizontal surfaces of the upper and lower platens, which created a stiffening response and ensured the stability of these very large displacements. The sensitivity of SU-FREI bearings to lateral displacement history and vertical pressure applied on the bearings were investigated. Regarding the latter parameter, it was found that the effect of variations in vertical pressure on the lateral response can be neglected when the SU-FREI bearings are subjected to relatively light vertical pressures such as considered for low-rise buildings.

S1301-1-5 電界砥粒制御技術を適用した新たな高能率両面研磨装置の開発(工作機械と生産加工(1))

Authors have been developed a novel double-sided polishing machine with high efficiency for IT devices. This machine consists of upper, lower platens and a pallet for work pieces. It has a new mechanism for high efficiency using circular moving each other parts. This machine has two major features. Firstly, the production efficiency obtained three times and more than the similar polishing area machine. Because this machine has no rotating center-shaft, the polishing area becomes larger than conventional polishing machine. Secondly, the high polishing rate is obtained using the water based with CeO_2 abrasives under AC. electric field.

Statin given perorally to adult rats increases cancellous bone mass and compressive strength.

Recently, it has been shown that statins increased cancellous bone formation and volume in 3-month-old rats and induced a minor decrease in osteoclast number. In the present study, one-year-old female rats were given simvastatin (10 mg/kg) or placebo daily for 3 months by a gastric tube. Specimens, 2.0 mm high, were cut transversely from the 5th lumbar vertebral body. The cancellous bone core diameters within the cortical shell of each specimen were delineated by a micro-CT scanner and then the cancellous bone was compressed in a materials testing machine between an upper and a lower platen with a diameter corresponding to the diameter of the cancellous bone core of each specimen. The cancellous bone volume was determined histomorphometrically on transverse sections. The cancellous bone volume in the simvastatin group (52.7 +/- 1.6%, mean value +/- SEM) was increased by 23% compared with the placebo group (42.8 +/- 1.7%). The compressive stress of the cancellous bone from the simvastatin group (31.8 +/- 2.7 MPa) was increased by 24% compared with the placebo group (24.1 +/- 1.9 MPa). No changes were found in cortical bone mass and strength after the statin treatment. In conclusion, statin given perorally to adult rats increased cancellous bone mass and increased cancellous bone compressive strength. The cancellous bone was found to possess normal biomechanical competence after the statin treatment.

Evaluation of axial shear test using plane strain simulations

The topic of soil anisotropy is still rather unfamiliar to the majority of geotechnical engineers. To clarify the effects that anisotropy can have on the response of soil specimens under plane unconfined vertical compression, the response of a simple anisotropic elastic specimen with inclined bedding plane and rough end platens is investigated numerically. In these simulations various lower platen boundary conditions, including axial shear control are applied. The results demonstrate that the response of the specimen depends on both the anisotropy of the material and the applied boundary conditions. For axial shear control the stress is shown to be homogeneous and coaxial with the sheared shape of the specimen in the central part. Also, the potential capabilities and limitations of axial shear control are investigated in an abstract way, giving support to the expectations of a novel elegant practical tool that could form the vital link in a chain of measures facilitating the incorporation of soil anisotropy in geotechnical engineering practice.

On using a Weissenberg rheogoniometer for oscillatory testing of stiff materials

When the Weissenberg rheogoniometer is used for oscillatory testing on stiff systems and experimental results interpreted in the conventional way, anomalous results occur. These are due to a lack of rigidity in rheogoniometer parts such as the air-bearing rotor, extension piece and lower platen holder, especially the latter. Future experiments on stiff systems will be facilitated by more rigid instrument members. Existing experimental results can be re-interpreted on the basis of the theory given.

The Rotary Forging Concept and Initial Work with an Experimental Machine

The rotary forging process is based on a recognition of the fact that the axial force required to effect a desired deformation during, for example, an upsetting operation may be reduced if the plastically deforming zone is confined throughout to a small region beneath the upper platen. The top portion of the workpiece is then rotated through this plastic zone thus resulting in a progressive deformation. An experimental rotary forging machine has been designed and constructed which incorporates a lower platen capable of axial movement only, whilst the upper conical platen is capable of rotation about the central axis of the machine and also about its own inclined axis. The principal design features of the experimental machine are described and the results of some preliminary experiments using the machine are presented. Operation of the experimental machine has demonstrated the feasibility of the process. The effect of the axial force on the rotary forging of cylindrical specimens having a height/diameter ( H/D) ratio of unity and for a fractional reduction of 0.5 is discussed. Pure lead at ambient temperature was used, as a model material, to simulate the rotary forging of steels in the approximate temperature range of 700-1400°C. A comparison is made between the axial force required to rotary forge and conventionally upset identical pure lead cylinders. It is shown that the optimum axial force required for slow rotary forging is a small fraction of that required for the conventional slow upsetting of circular cylinders having H/D ratios of less than unity.