Propagation mechanism of non-uniform distribution of stress and strain in tension test

Elastic-plastic finite element analysis is carried out on tension test to check the uniformity of stress and strain that highly influences the result of numerical analysis in forming processes. Usually stress is calculated by dividing the force by the cross sectional area of the specimen and strain is calculated by the change in a limited gauge length. Basic assumptions are that stress and strain distributions be uniform in the cross section and between two gauge points and the cross section lie between two gauge points. Result of numerical analysis shows that stress and strain distributions are not necessarily uniform especially for those material with poor work hardening ratio. Initiation and propagation of mechanism of this non-uniformity is analyzed to propose a method for a precise measurement of stress and strain

Unloaing and re-loading features of pre-strained steel at low temperature

In the present work the response of medium carbon steel is investigated experimentally and information on the features of initial loading, unloading, re-loading and inverse loading processes is collected. The experiment is a simple tension and compression test using a round specimen and stress-strain curves are drawn after giving strain histories to specimens. The value of Young’s modulus is measured from the stress-strain curve to evaluate the influence of pre-strain. Taking the result into consideration the intensity of predicted spring back of a thin sheet after bending process is evaluated

Estimation of response of steel sheet plated with thin hard layer

Elastic and elastic-plastic responses were examined of cantilevers made from a cold rolled steel sheet and made from the same sheet plated with a thin hard layer. Tension test of these sheets showed a non-linear behaviour even in the area of small strain and conventional linear theory of cantilever had to be modified. By extending this theory to a sheet plated with a thin hard layer Young’s modulus of plated layer was estimated. The range of estimated Young’s modulus was similar to those in previous works but material non-linearity, especially on the compression side, must be measured more precisely

Influences of finished geometry of specimen for compression test on the stability of testing and precision of measured stress and strain

This paper deals with the influence of the specimen geometry on the precision of measured stress-strain curve on the compression side. Cylindrical specimen is adopted after ASTM-E9 89a and laboratory experiment and elastic-plastic FEA are carried out to evaluate the influence of the degree of parallelism of end surfaces. Present tolerance value of 0.5/1000 for the inclination of end surface can be relieved up to 6/1000

Experimental and numerical analyses on the characteristics of twin skew rolling

Elastic-plastic FEA was carried out on the rolling process of twin skew rolling for a blooming mill to evaluate the influences of roll diameter, skew angle, and coefficient of friction on the suppression effect of porosities in the vicinity of centre axis of the material. Rolling by using a proto-type mill and modelling clay was then carried out to verify the validity of numerical analysis. Both results showed that the larger the roll diameter, and also the larger the coefficient of friction, the higher the suppression effect of porosities

Finite element analysis of tube drawing process with diameter expansion

This paper presents a tube drawing process with diameter expansion for producing a thin-walled tube effectively. In this proposed process, the tube was flared by a plug pushing into the tube, and then the tube was expanded by drawing the plug in the tube axial direction with chucking the flared tube edge. Optimum plug shape, such as the plug half angle and the corner radius, was investigated by a series of analyses using the finite element method (FEM) for improving the forming limit and the dimension accuracy. At first, a friction coefficient was determined to 0.3 by a comparison of the flaring limit between the analysis and the experiment of the tube flaring. As a result of the analyses in the drawing with the diameter expansion, the forming limit was high when the plug half angle was set to 18~30°. The thickness reduction ratio increased with an increase in the expansion ratio and the plug half angle. In addition, the overshoot, which is a difference between the plug diameter and the tube inner diameter after the drawing, was prevented by using the plug with the corner radius of 20 mm

Estimation of lubricity by numerical method on surface of nbc-reinforced tool for hot steel rolling

Investigation was carried out on the lubrication mechanism of NbC-reinforced tool for hot metal working. Observations on the surface of reinforced tool carried out after use to clarify that the tool surface was covered with a kind of oxide. X-ray analysis showed that the oxide was Nb2O5. Laboratory experiment was carried out to grasp the condition of heating in air for the transformation of NbC to Nb2O5, and following the condition NbC powder was heated to obtain Nb2O5 powder. Hot rolling experiment of steel sheet followed. Prior to rolling Nb2O5 powder was placed on one side of the sheet on the inlet side, and the curl of the rolled sheet was measured. Elastic-plastic FEA was carried out to specify the coefficient of friction at high temperature. The numerical result well matched to the experimental result when the value of coefficient of friction of Nb2O5 was 0.15. The value is equivalent to the value of graphite which is a well know good lubricant at high temperature

T2緩和時間を指標とした15％最大筋力時の手関節伸展運動筋の解析

骨格筋緩和時間(T1, T2)を指標としたMRI法は，表面筋電図法，超音波法に加え新しい骨格筋の運動分析法として注目されている．本研究では，物を把持するなど日常生活で重要な手関節伸展運動について検討した．健常人8名を被験者とし，最大等尺性収縮筋力の15％の等張性収縮運動の前後でのT2強調画像とT2の変化，および運動後25分の回復を測定した．測定筋は，短橈側手根伸筋，総指伸筋，小指伸筋，円回内筋，尺側手根伸筋，深指屈筋，浅指屈筋，尺側手根屈筋，橈側手根屈筋，腕橈骨筋とした．運動後T2強調画像から活動筋を弁別した．短橈側手根伸筋，総指伸筋，小指伸筋にT2の延長を認めた（P＜0.01）．その後，緩やかに短縮したが，短橈側手根伸筋と総指伸筋では25分後までT2の延長を認めた．尺側手根伸筋，円回内筋は延長傾向を認めたが，有意ではなかった．主動筋の短橈側手根伸筋に対して，総指伸筋，小指伸筋に協同作用としての活動が確認できた．屈筋群である尺側手根屈筋，橈側手根屈筋，深指屈筋，浅指屈筋，腕橈骨筋は非活動であった．以上より，T2を指標としたMRI法により手関節運動筋の運動解析が可能であることが示された

Aging-Affected MSC Functions and Severity of Periodontal Tissue Destruction in a Ligature-Induced Mouse Periodontitis Model

Mesenchymal stem cells (MSCs) are known to play important roles in the repair of lost or damaged tissues and immunotolerance. On the other hand, aging is known to impair MSC function. However, little is currently known about how aged MSCs affect the host response to the local inflammatory condition and tissue deterioration in periodontitis, which is a progressive destructive disease of the periodontal tissue potentially leading to multiple tooth loss. In this study, we examined the relationship between aging-induced impairment of MSC function and the severity of periodontal tissue destruction associated with the decrease in host immunomodulatory response using a ligature-induced periodontitis model in young and aged mice. The results of micro computerized tomography (micro-CT) and histological analysis revealed a more severe bone loss associated with increased osteoclast activity in aged (50-week-old) mice compared to young (5-week-old) mice. Immunostaining analysis revealed that, in aged mice, the accumulation of inflammatory T and B cells was higher, whereas the percentage of platelet-derived growth factor receptor alpha (PDGFR alpha)(+) MSCs, which are known to modulate the apoptosis of T cells, was significantly lower than in young mice. In vitro analysis of MSC function showed that the expression of surface antigen markers for MSCs (Sca-1, CD90, CD146), colony formation, migration, and osteogenic differentiation of aged MSCs were significantly declined compared to those of young MSCs. Moreover, a significantly higher proportion of aged MSCs were positive for the senescence-associated beta galactosidase activity. Importantly, aged MSCs presented a decreased expression of FAS-L, which was associated with a lower immunomodulatory property of aged MSCs to induce T cell apoptosis in co-cultures compared with young MSCs. In summary, this is the first study showing that aging-induced impairment of MSC function, including immunomodulatory response, is potentially correlated with progressive periodontal tissue deterioration