Estimation of Mechanical Strength of Main Frame Made of Molded Plywood on a Wheelchair

(Received on March 6, 1995)

Hiroshi NASHIHARA

The development of a wheelchair fabricated primarily of wood, using the plywood molding technique, which meets the functional and psychological requirements of users, is nearing the stage of practical use and production. The parts related to seating are constructed using reciprocal laminated wood, and main frames are constructed using laminated wood (LVL). In this study, the mechanical strength of the LVL main frames is investigated. It is confirmed that LVL laminated beech has the average material factor of pure beech, using material testing procedures corresponding to JIS. Strength test results of the L- and T- shaped LVL frames are compared to those of metal pipe frames with the same shape used in the conventional wheelchairs. It is estimated that the strength of LVL frames is equal to or greater than that of metal pipe frames. Mechanical strength of the LVL main frame under dynamic loads is analyzed using finite element method software. When a person sits down rapidly on the seat of a wheelchair, the maximum stress is about 1/3 of the yield stress. It is confirmed that LVL main frames have reasonable shape, size and composition.

Keywords:molded plywood forming, LVL laminated wood, LVL main frame, mechanical strength, design, wheelchair

Rolling Characteristics of Oval Caliber Roll
-Bar Rolling in 4-Roll Mill II-

(Received on May 13, 1995)

Kouichi HIRAKI, Shigenobu SUZUKI, Shigeharu OCHI and Shinji KAMOTO

Recently, size free rolling an d fine rolling have been highly required in bar and wire rolling process. Generally, a 4-roll rolling process is inferior to a 2- or 3-roll rolling process in area reduction, but superior in precise rolling capability. However there have been very few reports about the 4-roll rolling Process. The deformation mechanism and characteristics of this process are thus not well understood. In this work, rolling characteristics are examined by means of experiments which are conducted in the process of high reduction during the first pass and finishing during the second pass. As a result of the experiments, the following findings are obtained. 1) Lateral reduction increases with an increase of area reduction. 2) Rolling load and rolling torque increase lineally with an increase of area reduction. 3) In the case of a bar 25 mm in diameter, after 2 passes, about 25 % reduction in area is attained and in this case the roundness is 0.2 mm.4) With an increase of area reduction, the rolling load factor becomes almost constant.

Keywords:rolling, bar rolling, 4-roll mill, oval caliber, forming property, roundness, lateral spread, rolling load factor

Some Features of Shear Band and Edge Crack in Rolled Al Alloy

(Received on June 5, 1995)

Ryuuta ONODERA, Kimihiko KATOH, Shuuichi MATSUNAGA, Masatoshi ARAMAKI and Kenji HIGASHIDA

To clarify (1) the change in the angle of shear band with increase of rolling reduction, (2) the effect of free surface on the activity of shear band and (3) the relation between the shear band and edge crack, an experimental study has been carried out. The angle of a freshly generated band is high (40-48‹), and decreases with increase of rolling reduction. Almost all shear bands lose their activity when the angle decreases to 30-25‹). These results suggest that the peculiar angle of 35‹, often reported in the literature is merely a mean value during the lifetime of a band. In order to investigate the surface effect, two types of specimen are used-I one (surface specimen) has a 0.2mm thickness of the side surface removed by polishing after pre-rolling, and the other (inside specimen) has a thickness of 2mm removed. By re-rolling these specimens it is shown that the density of shear bands is lower and the shear displacement per band is larger in the surface specimen than in the inside one. Edge cracking occurs at the junction of the freshly generated band with high angle (45 ‹) and the old band which is still active though the angle is low (near 25 ‹).

Keywords:shear band, edge crack, rolling, Al alloy, band angle, shear displacement

Influence of Kind and Orientation of Surface Defect on Tensile Behavior of Aluminum Sheet Metal
-Influence of Surface Defect on Forming Limit of Sheet Metal … -

(Received on June 15, 1995)

Tetsumaro HIROI and Hisashi NISHIMURA

Tensile behavior of specimens of both as-received and annealed pure aluminum sheet metal with three kinds of a single surface defect which is a thin groove at right angles to the tensile direction, is investigated experimentally. Tensile testing of the materials with the defect inclined in the tensile direction is also conducted. It is observed that the influence of the kind and orientation of the defect on the load- elongation curve is not manifested until rupture occurs. The existence of a limiting nondimensional defect depth (ƒ¿e=h/t) is observed in all cases; rupture elongation does not decrease in the region shallower than a .. a . of the annealed material with an indented defect was 1-2% greater than that of the annealed material with all other kinds of defects, because the work-hardened area around the defect affects the load-bearing capacity. The indented defect in the as-received material, in contrast, decreases a. because work-hardening decreases the material's ductility. a. for a ductile material depends only weakly on defect orientation, whereas a. for a less ductile material is influenced strongly. As a result, mechanical properties can be measured when defect depth is less than 2% of the thickness of the sheet.

Keywords:tension test, surface defect, rupture elongation, kind of defect, orientation of defect, aluminum sheet metal.

Simple Measurement of Surface Deflection of Sheet Metal by Reflection of Line Grating

(Received on june 23, 1995)

Linsheng LIU, Takao SAWADA and Makoto SAKAMOTO

A new method for noncontact measurement of the surface deflection of sheet metal is proposed, where a parallel straight line grating is set perpendicularly on a base plane . The grating is reflected on the surface of the sheet metal, and some of the straight lines become curved at certain parts. The deviation of the curved lines from the straight lines is represented by (5, which indicates the surface deflection of the sheet metal. Two equations representing the reflection of the grating on the glittering metal specimen like a mirror and the focussing on the sensing plane of camera are introduced. When the grating is reflected on a flat surface of the sheet metal, the tilt angle and the location of the camera are calculated. Then the slope angle 0 and the reflection point on the surface of sheet metal are calculated from these equations using the Newton-Raphson method. A surface deflection on a flange generated by embossing is measured by the proposed system and a profile measuring apparatus. Both results are in good agreement. Resolution of the slope angle 0 of the sheet metal in the proposed system is 3xlO-4 rad from the numerical analysis.

Keywords:measurement, profile measurement, surface deflection, noncontact measurement, measurement of angle, reflection of grating, image processing.

Mode in Localized Necking

(Received on June 28, 1995)

Hitoshi MORITOKI and Eiki OKUYAMA

On a localized necking plane a discontinuous velocity gradient can occur in a continuous velocity field. One of the necking planes has equivalent planes with the same direction cosine, in magnitude, of their unit normal to the principal axes as that of the original plane. These planes have equal potential for becoming a necking plane. The simultaneous activation of these planes iii localized necking results iii no difference in the principal directions on both sides of the necking plane. Even if a discontinuity occurs, the components of the velocity gradient parallel to the plane must be continuous in order to maintain the continuity of velocity. hence, in general, only two modes, mode P and mode 0 are permissible for the necking plane. These modes are compared with the mode used in the analysis by Storen and Rice 9), which is usually inapplicable, because a discontinuity of the volumetric strain rate occurs across the necking plane. The equilibrium condition between the two sides of the necking plane used by Storen and Rice must be modified. The modified conditions of mode and equilibrium for localized necking exactly coincide with one of the universal criteria resulting from the collapsing condition for unique solutions.

Keywords:Plastic Instability, Localized Necking, Necking Mode, Criterion for Ductility

Inside Diameter Accuracy of Extruded Pipes by Porthole Die
-Study on Improvement in Quality of Hollow Extrusions 11

(Received on July 22, 1995)

Satoshi MURAKAMI, Norio TAKATSUJI, Mitsugu TOKIZAWA, Kazuo MUROTANI, Kenji MATSUKI and Kiyoharu HASHIMOTO

The effect of relative location of portholes and number of portholes on the circularity and the welding of an extruded pipe for a square cylinder is investigated by the extrusion test. The welding strength of the extruded pipe obtained from the expansion test is independent of the relative location of portholes, and is almost the same value for the same number of portholes. 'Me circularity of the extruded pipe can be improved by locating portholes on a thinwall area of the pipe and increasing the number of portholes. 'Me accuracy of the inside diameter of the extruded pipe corresponds to the shape of the plastic defomation zone of the bottom welding chamber, and circularity is improved with better accuracy of the circle shape of the plastic deformation zone of the bottom welding chamber.

Keywords: extrusion, porthole die, extrusion pressure- welding strength, extruded pipe, welding chamber, number of portholes, circularity

Decrease of Density and Its Recovery by Heating in Cold-Deformed Steels

(Received on August 14, 1995)

Kenjy HIBI, Minoru IKEDA and Shinsaku ONODERA

A new approach is made for studying the internal structure and integrity of cold-forged steels, by measuring the decrease of density induced by cold forging. A set of precision density measurement apparatus was prepared which ensures an error of }0012g/CM3 or }0.015% or less for a steel specimen of 30g or larger. Specimens for density determination were cut out from compression, forward extrusion and tension test pieces. In the compression specimens, which were compressed within the upsetting Iimit ( ranging from 60 to 75%), the decrease of density amounted almost linearly to 0.20%, with differences depending on steel designations and their prior treatments, and noteworthily, the decrease was almost recovered by heating up to 650'C and above. In the extrusion and tension specimens, considering the much more heterogeneous nature of deformation, a threshold of density change was sought together with microcrack formation in and around pearlite before the appearance of macrocracks; in both tests the decrease of average density reached 0.4%. Three flanged shafts were subjected to the measurement of density change using the specimens cut from the flange portion. Decrease of density by cold forging and recovery of density by annealing were confirmed in the products, which should be of general use in the assessment of and QA for precision cold- forged steel products.

Keywords:forging, cold forging of steel, reduction of density in cold-forged specimens and@its recovery by heating, and a verification for actual products.