Free Contraction Research Articles

Significance of filler content to properties of silicone impression materials

The effect of filler content on handling characteristics, mechanical properties and accuracy of addition curing silicones was investigated on 7 sets of experimental materials with filler contents between 0 and 61.5% by weight. The consistency increased linearly with the amount of filler; working and setting times were consistent irrespective of the filler content. Exponential relationships were found between filler loading on the one hand and Shore A hardness and stiffness on the other. The linear free curing contraction was approximately 0.05% for all materials tested while the coefficients of thermal contraction linearly decreased with increasing filler content. Cooling of impressions of a standardized metal preparation from 37°, to 23°C had a tremendous impact on accuracy. Adequate die accuracy was obtained only when impression and model were produced at the same temperature.

Beta-adrenergic regulation of contractility and protein phosphorylation in spontaneously beating isolated rat myocardial cells.

Spontaneously beating heart myocytes were prepared from adult rat ventricular tissues to study the correlation between beta-adrenergic receptor-stimulated changes in contractile performance and protein phosphorylation in vitro. The plasma membrane of isolated myocardial cells was permeabilized by saponin in the presence of EGTA and Mg-ATP. The permeabilized myocytes, which formed a homogeneous cell population, retained the rod-cell morphology of heart cells in situ and showed spontaneous cyclic contractions. Their contractile activity in response to extracellularly added cAMP mimicked the effects caused by beta-adrenergic stimulation of the whole heart: both the frequency and longitudinal velocity of free contraction and relaxation of the cells increased. Similar increases were observed when beta-agonist, isoproterenol, and GTP were added to suspending medium. In addition, isoproterenol maximally enhanced the adenylate cyclase activity of the cells in the presence of GTP. Both of these effects of isoproterenol were completely blocked by the beta-antagonist propranolol. cAMP-mediated phosphorylation of proteins in the permeabilized myocytes was investigated under conditions in which the beating frequency increased. cAMP elevated the phosphorylation level of five proteins; three of them with apparent molecular masses of 24, 15, and 12 kDa were membrane proteins and the other two with apparent molecular masses of 150 and 28 kDa were myofibrillar proteins. The 24-kDa phosphoprotein dissociated into 12-kDa molecules when boiled in sodium dodecyl sulfate, suggesting that these proteins are oligomeric and monomeric forms of phospholamban. The phosphorylation of these five proteins was stimulated by isoproterenol. The effect of isoproterenol was enhanced by GTP but completely blocked by propranolol. The time course of their phosphorylation correlated well with that of the increase in the beating frequency of the cells; both were measured after the administration of isoproterenol and GTP. When propranolol was added after the start of the stimulation by isoproterenol, only phospholamban and the 15-kDa protein were rapidly dephosphorylated in close correlation with the decrease of the beating frequency. These results demonstrate for the first time that the permeabilized myocytes retain the functional beta-adrenergic receptor and cellular responses to beta-adrenergic stimulation. They also suggest that cAMP-mediated phosphorylation of proteins, possibly phospholamban and/or the 15-kDa protein, is involved in the increased contractile activity of permeabilized heart cells.

The effects of capillarity on the contraction coefficient of a jet emanating from a slot

This study is concerned with the effects of surface tension on the steady potential flow of a liquid issuing from a two-dimensional slot with inclined walls. The mathematical problem, which is characterized by a nonlinear boundary condition along the free streamline, is solved using a novel numerical technique based on the fast direct Poisson solver. Numerical solutions were obtained for various Weber numbers and slot angles, and the results are compared with the free streamline shapes and contraction coefficients of the corresponding classical potential solutions without surface tension, and with some available theoretical results. When the numerical grid size is reduced or when the Weber number is sufficiently small, undesirable standing waves appear on the free surface that violate a causality condition. The cause of these waves was examined. A criterion was found for the occurrence of the waves.

Viscoelastic and thermal behaviour of partially compatible polymer blends polycarbonate/tetramethylpolycarbonate

Differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) measurements show that, in the case of polycarbonate (PC) with tetramethylpolycarbonate (MPC), the homopolymers are miscible up to 70% PC weight fraction; at higher PC content, an additional PC phase appears. The partial miscibility of PC and MPC has been confirmed by ultrasonic attenuation measurements and scanning electron microscopy. The viscoelastic behaviour of these blends has been correlated with the blend composition and compatibility. The free volume contraction, found to explain the variations of glass transition temperature and viscosity with concentration, suggests strong intermolecular interaction in the compatible range.

Drying Mechanics of Gels

ABSTRACTA model is presented for the stresses and strains that develop in a gel during drying. The driving force for shrinkage is assumed to be the interfacial energy, and the gel is considered to be viscoelastic. The liquid seeks to flow into the dry region of a gel in order to replace the solid-vapor interface with a solid-liquid interface having lower specific energy. This creates a “redistribution pressure” that causes the wet region to contract. The free contraction rate can be calculated by equating the decrease in surface energy with the energy dissipated in viscous flow as the gel contracts. The permeability of the gel to the liquid in the pores is especially important in the early stages of drying, and may control the contraction rate. The model allows quantitative predictions of contraction rate and stress during drying. In this paper, the model is applied to a plate drying from both sides.

ＴＲＣ試験及びＲＲＣ試験の力学的特性と相関性

TRC and RRC tests are basic testing methods for studying cold cracking sensitivity of materials. The restraint condition of RRC test is clearly defined but that of TRC test is not. In contrast with this, the testing method of TRC test is much easier than that of RRC test, and an arbitrary loading diagram after weld can be applied in the test.Therefore, it is very important and useful to clarify the dynamical characteristics of both tests and their corelation.For this purpose, a series of thermal elastic-plastic analysis by the finite element method was carried out.The results are summerized as follows.(1) There is no essential difference between dynamic al characteristics of TRC test and of RRG test if the loading process in TRC test is chosen as similar as the process of development of restraint stress in RRC test.(2) In TRC test, stress distribution in the throat section may be determined only by the final restraint load, but plastic strain distribution is affected very much by the loading process.(3) In order to get stress and plastic strain distribution in the throat section, which are very similar to those of RRC test, it is necessary to impose in TRC test a loading process as indicated below, (a) the load may be applied when heat begins to be transmitted out of the restraint length.(b) the load may reach at the final value at a temperature which the corresponding RRC test ends.(c) the final load may be equal to that of RRC test.(4) The corelation between two tests is obtained as follows, (a) the free contraction S is measured.(b) a tensile test is conducted for a weld joint of 2l length.(c) the elongation of the specimen should be the same as S.

Right ventricular dysfunction and surgical outcome in postinfarction ventricular septal defect

The data of 50 consecutive patients treated for postinfarction ventricular septal defect were reviewed. Cardiac catheterization was carried out in all patients and surgical repair was undertaken in 32 patients. The main factors affecting surgical outcome were the site of infarction and the extent of right ventricular damage. Anterior myocardial infarction carried a better hospital survival rate than inferior infarction (67 and 31%, respectively). Poor right ventricular free wall contraction, present in 44% of anterior infarctions and 71% of inferior infarctions carried a high mortality. Eighty per cent (12/15) of patients with good right ventricular contraction survived operation compared to only 24% (4/17) of patients with poor right ventricular contraction. Surgery within 24 h to 14 days of infarction carried a survival rate of 50% (7/14), similar to that in patients operated on more than two weeks following infarction (9/18). Seventeen out of 18 patients who did not undergo surgery either died suddenly before scheduled operation or were considered too poor a surgical risk. Of these, 12 patients died within one week of infarction and five patients survived between two weeks and three months. Early surgical repair should therefore be considered in all patients with postinfarction ventricular septal defect, the prognosis in patients with good right ventricular contraction being excellent.

Free radicals in tetanic activity of isolated skeletal muscle

1. 1. The concentration of the free radicals in muscle tissue mitochondria changes with the phase of muscle contraction. 2. 2. Potassium cyanide (KCN) influences the shape of the isotonic tetani mechanograms; the contraction is still strong and qualitatively comparable in amplitude to untreated controls. 3. 3. On the other hand, the correlation between the free radical concentration and muscle contraction is lost. 4. 4. The free radical concentration in isolated mitochondria is influenced by KCN and potassium ferricyanide. 5. 5. The free radical concentration changes due to the electron flow in the respiratory chain. 6. 6. Inhibition of the respiratory phosphorylation by KCN could affect the free radical level.

Mechanism of extraneuronal adrenaline release induced by K+ -free medium and ouabain, but not by high KCl in vas deferens of guinea-pig and rat

The effects of K+-free medium, ouabain or high KCl on the contractile response and spontaneous efflux of adrenaline were analyzed in denervated guinea-pig or rat vasa deferentia preloaded with 3 x 10(-5) M (+/-)-adrenaline. The K+-free medium-induced contraction of guinea-pig tissues was related to the concentration of adrenaline used during preloading and was suppressed by the addition of 2.5 mM Rb+ but not by 2.5 mM Cs+. The contractile effects of K+-free medium and 10(-5) M ouabain, but not the response to high KCl, were prevented by 5 x 10(-6) M phentolamine or 3 x 10(-5) M deoxycorticosterone. These contractions, therefore, appear to be mediated by adrenaline released from the extraneuronal compartment. The K+-free medium- or ouabain-induced contractions of denervated rat vasa deferentia were small in comparison with those of the guinea-pig tissue. The amount of spontaneous efflux of adrenaline from the guinea-pig preparation was significantly enhanced by omission of K+ or by 10(-4) M ouabain but not by 80 mM KCl. K+-free medium and 3 x 10(-5) M ouabain merely elicited a small membrane depolarization accompanied by a slight decrease of membrane resistance in the guinea-pig vas deferens, whereas 30 mM KCl markedly altered these electrical parameters. From these findings, it is suggested that the rapid increase in extraneuronal amine release following inhibition of Na+-K+-ATPase may be due to some direct effect of K+ deficiency or of ouabain on the binding between the enzyme and the catecholamine rather than to alterations of membrane properties as a consequence of enzyme inhibition.

146 LONG TERM LEFT VENTRICULAR POSTERIOR WALL ECHOCARDIO- GRAPHIC CHANGES IN DUCHENNE MUSCULAR DYSTROPHY

Cardiac pathology in Duchenne's muscular dystrophy (DMD) is principally left ventricular posterior wall (LVPW) fibrosis. The aim of this study was to track long term LVPW echocardiographic (echo) changes in DMD. Echoes were recorded each 12 months from 19 boys with known DMD over 3 years and compared to controls. LVPW endo- and epicardium were digitized and % thickening and % thinning at standardized time intervals were determined; 15/19 had two-dimensional echoes. As previously reported, impaired diastolic relaxation was an early finding. The ratio of peak systolic LVPW to end diastolic LVPW was 2.06 (controls) to 1.83 (boys with DMD) (p<.01), but a given boy's ratio was not predictive. All 19 had LVPW thickness, adjusted for body size, below the control mean (p<.01). The major finding was that two wall pattern groups emerged: Group I-LVPW thickness increased normally with time and body surface area but at a low percentile curve. Group II-LVPW decreased progressively and in 4, almost no systolic LVPW thickening was found. Two-dimensional echoes were studied for change in cavity size during contraction. All Group I patients had normal two-dimensional echoes. All Group II patients had abnormally decreased LV free wall contraction. Sequential abnormal findings in DMD patients are impaired LVPW relaxation, decreased LVPW thickness in systole and end diastole, and a contraction impairment imaged with two-dimensional echo.

146 - Ca free contraction in rat uterine smooth muscle.

146 - Ca free contraction in rat uterine smooth muscle.

ＨＴ８０鋼溶接部不溶着切欠からのぜい性破壊発生特性

To assess the degree of embrittlement in a transformed HAZ and the possibility of additional embrittlement caused by hot straining, brittle fracture initiation behavior from a notch of poor penetration in a weldment of HT 80 steel of 31 mm thickness has been investigated by measuring critical crack opening displacement (COD) at fracture. Three points bend specimens of 15 mm thickness were extracted from butt joint with weld defect of poor penetration, and the tip of the notch was located on a fusion' line in modified single=bevel joints, or, it was located on a weld metal in modified single-Vee joints. In these butt joints the degree of hot straining was altered by changing a intensity of tensile restraint in modified Lehigh restraint test specimens.Heat input had large effect on the fracture toughness of fusion line, and reference temperature (Tr: critical COD of 0.25 mm) was markedly riled with increasing the heat input up to 42 KJ/cm. Fusion line and coarse-grained region of the HAZ was susceptible to hot straining embrittlement whereas the weld metal was not. The quantitative relation between the intensity of tensile restraint and the increase in reference temperature (ΔTr) was obtained. Small region ahead of the poor penetration in the joint of high tensile restrain received severe hot straining and showed high Tr temperature, and it was concluded that this severe hot straining was caused by restricting the free contraction of the weldments.In the as welded and hot strained conditions, all the specimens with notch of poor penetration were more brittle than the specimens with fatigue pre-crack extracted from parent material, and thermal stress relief had disadvantage effect on fracture toughness of fusion line. In the most specimens extracted from modified double-bevel joints, crack propagated along fusion line.

鋳造体の適合性におよぼす中子の影響

All the casting prepared for the present experiment could not be produced without any shrinkage and deformation. Although asbestos lining surely decreased the cast shrinkage, the casting could almost never become larger than the wax pattern. Under the circumstances the conventional crown model of the casting, of which the core height is three quarters of the outer side wall height, could have larger concave than the wax pattern by lining the ring with two folds of wet asbestos or more. Such a deformation favorable for the good fitness may possibly be caused by larger size of the core. Results of the pressure measurement on the pattern in the investment revealed that the anisotropic and heterogeneous setting expansion of the investment in the casting ring would be induced by the presence of the wax pattern itself. The investment is partitioned by the pattern into two parts, the core portion and the portion between the pattern and the ring wall. Each portion of the investment would seem to behave somewhat independently in setting. The well fitting of the crown casting may be attributed never to the full compensation for the cast shrinkage, but to the favorable deformation caused by the beneficial expansion of the core and the impediment of it to the free contraction of the cast alloy in solidification.

Fluid Flows from Axisymmetric Orifices and Valves

The present finite element analysis seeks an approximate solution for the minimization of a functional which is related to the axisymmetric irrotational flow of an ideal fluid as it passes through orifices, valves, or nozzles and emerges as a free-surface jet. The resulting set of linear equations for the nodal values of the velocity potential is symmetric and banded, which can be efficiently solved by the computer. Location of the free surface profile requires the use of an iterative scheme, which is apparently always convergent. Then velocity and pressure distributions can subsequently be evaluated quickly. Curvilinear interior solid boundaries cause no computational difficulties, although results near a convex surface tend to be less accurate than results in other regions. The method can produce good accuracy for such quantities as free surface profiles, and contraction and discharge coefficients; in most, but not all, flow regions it will also produce good results for velocity and pressure distributions. Computer execution time is generally modest.

The Behavior of Fabrics in Shear

The effect of heat-setting on the properties of a nylon monofil fabric in shear has been investigated, and considerable changes have been found to occur. These changes particularly depend on whether heat-setting is done with the specimen held at fixed dimensions or allowed free contraction. Photographs of the actual contact area at fila ment crossovers are presented to interpret many of the resulting shear properties. It has also been found that bending properties of the filaments were unaffected by heat-setting, and that the bending stiffness of the filaments may significantly contribute to the fabric shear resistance. In addition, a new dynamic method of measuring the cyclical/energy loss of the fabric in shear has been devised. General agreement was found between loss values thus obtained, and with those obtained by the static method described in an earlier paper (Part I).

溶接継手の外的拘束に影響する要因について

Weld cracking is influenced by both reaction stress during cooling and properties of weld metal and heat-affected zone. The problems of weld cracking, therefore, should be explored not only from metallurgical standpoint but also from standpoint of reaction stress. Researches on effect of reaction stresss during cooling or restraint on weld cracking are now undertaken by the authors, especially for first-pass-weld-cracking of restrained welds of some mild and high strength steels. At earlier stage of the research project, informations on what factors influence to reaction stress under restraint were wanted for reasonable research planning. The present paper was prepared as preliminary informations for the subsequent test planning.In a restrainning system shown in Fig. 1 shrinkage force will be produced by hindered contraction or extension of first-pass weld metal during cooling. Analytical investigation was conducted on the extension of weld metal. The anaiysis is based on the assumptions that behavior of mother plate (B) and restraining members (C) is elastic during cooling, however, in the weld metal will be produced some plastic deformations under the stress-strain relation as shown in Fig. 3. The extension (λw) of weld metal at a given temperature below about 300°C is obtained bypwhw/ph⋅λwn+λw=Swhere ph and pwhw are rigidity or force per unit weld length required for unit extension of mother plates and weld metal respectively, and S is free contraction between restrained length (l) of mother plate. Relations of λw versus rigidity ratio pwhw/ph are shown in Fig. 4 for a few values of S. Larger extension of weld metal will be produced under smaller rigidity ratio and larger free contraction.Free contraction S will be influenced by heat input and overall cooling behavior of mother plate of length l. Under a given heat input the overall cooling rate or heat loss from the mother plate of length l will be increased as the decrease of heat capacity or length (l) and thickness (h) of mother plate.It will be concluded, therefore, that under a given heat input reaction stress of weld metal at a given temperature is influenced by the following factors ;1) restraint coefficient (p), which contains restrained length (l) and ratio of sectional area of mother plate to restraining members.2) thickness (h) of the mother plate.3) restrained length (l) of the mother plate.4) rigidity of weld metal (pwhw).Figs. 8 and 9 show some calculated examples of the effect of l and h on the extension of weld metal.

Thermal Fatigue Combined with Mechanical Stress

The strength characteristics of metallic materials which are to be subjected to thermal stress cycling superimposed on mechanical stress is of interest from the practical point of view in design purpose. The authors have pointed out in the previous papers an importance of the consideration of the problem in relation with the strength characteristics of materials in cyclic mechanical strain fatigue and creep rupture at elevated temperature, and have presented some analytical and experimental works in this line.In the present paper, the thermal fatigue combined with steady mechanical stress is treated. The elongation of material is not prohibited and the mechanical mean stress does not decrease with number of cycles of thermal stress. There is another mode of combination of mechanical stress and thermal stress cycling, that is, both of mechanical and thermal stress are cycling. This category of problem has been discussed in another paper of the authors. The interest of the present study is placed on the former problem, and the fracture life and deformation of austenitic stainless steel subjected to cyclic thermal and steady mean stress is discussed in connection with both strength characteristics of fully reversed thermal stress cycling and simple creep rupture.Test condition of combination of cyclic thermal stress amplitude Δσ and steady mechanical stress σm is characterized by the stress ratio Δσ/σm. Thermal stress in hollow cylindrical specimens arose by prohibiting free longitudinal expansion and contraction of the specimen subjected to temperature cycling. The mechanical mean stress in tension is applied by pull head mechanism. In the test of small stress ratio, specimen elongates and it causes relaxation of the mean stress. In order to realize the test condition of thermal fatigue under mean steady stress, the relaxation of mean stress must be compensated. This function is realized by a relay mechanism, in which a pulling head worked by the signal sent from the electric circuit of wire strain gage mounted on a weighing bar that is installed in series with specimen. The lower stress level in the cycling of combined stresses is taken as the basis of the automatic control of combined stresses, and the control unit is set to maintain the level of the minimum stress constant.From the present study the followings are concluded:(1) Fracture life of materials subjected to thermal fatigue combined with tensile mean stress can be predicted approximately from both test data of completely reversed thermal stress cycling and simple creep rupture, by employing the criterions of fatigue damage and life consumption in creep rupture for the material subjected to simultaneous cyclic variation of stress and temperature. The analytical results are in good agreement with experimental results on 18-8 Cb stainless steel where Δσ/σm is chosen as 0.5, 1 and 2.(2) Tensile deformation of materials subjected to combined thermal cycling and tensile mean stress, where tensile mean stress is larger compared with thermal stress amplitude, is estimated from the test data of simple tensile creep, by using the principle of strain hardening for the material subjected to simultaneous cyclic variation of stress and temperature. The analytical results are approximately in agreement with experimental results where Δσ/σm is smaller than unity.

22Cr-1Cuフェライト系および18-8オーステナイト系不銹鋼の熱疲労

The problem of failure of structures subjected to cyclic thermal stresses is of interest both from fundamental and also practical points of view. The thermal stress arises because of thermal strain which is produced in consequence of constraint of free thermal expansion or contraction of structures. Thus, the thermal strain is an independent variable in the present problem.The authors, as well, have been interested in the problems of lifetime of metals subjected to varying temperature or combined variation of temperature and stress, and have published some reports in this line. The present study is undertaken to obtain information regarding fundamental problems of thermal cycling of heat resistant alloys. For this purpose, a thermal cycling test apparatus was manufactured and the tests were performed, using 22Cr-1 Cu ferritic and 18-8 austenitic stainless steels. The followings are the results from our studies:(1) The apparatus for thermal cycling give good patterns of both temperature cycling and thermal stress cycling for the thermal cycling test.(2) Temperature dependency of failure life of thermal cycling on AISI 318 type stainless steel is not so remarkable as compared with the case of creep rupture life under temperature cycling for the same material.(3) From a series of thermal cycling tests for mean temperature of 650°C on 318 type stainless steel, it is found that variation of wall thickness of hollow specimen from 0.5mm to 1.5mm has no significant effect on the failure life.(4) If mean temperature is adopted as a basis of test temperature, the data of tests where minimum temperature is taken during temperature cycling as a basis of test condition can be estimated as well, provided that temperature dependency of failure life of thermal cycling is known.(5) In thermal cycling tests, adoption of total strain amplitude which is to be composed of elastic and plastic strains is practically more useful than that of plastic component of strain.(6) From the present experiments some pertinent problems which are to be developed are clarified.

収縮阻止による熱応力が残留オーステナイト量に及ぼす影響

Thermal contraction in cooling was prevented as a representation of a special thermal stress in the surface layer of steel induced by quenching. The effects of such thermal stress on retained austenite (γR) were as follows. (A) Experiments on high carbon alloy steels. (1) The tensile stress induced by preventing the thermal contraction increased linearly with decreasing temperature and indicated the maximum value at Ms temperature, that was about 10 kg/mm2. (2) The amount of γR was markedly increased by preventing the thermal contraction. This is contrary to the expectation from the mechanism of martensite transformation which has been interpreted from the criterion of shearing stress. (3) The effective temperature range of stress on γR existed between 100∼150°C above Ms point and room temperature. Also the most effective temperature lies in the vicinity of Ms temperature. (4) The rise of cooling velocity at the range of above Ms temperature increased the amount of γR as the result of increment of induced tensile stress. (5) At below Ms temperature, the rise of cooling velocity decreased the amount of γR, similarly to free contraction cooling. Therefore it appears that there is no effect of stress on the thermal stabilization of austenite. (B) Stabilization of austenite by preventing the thermal contraction was not observed in medium and low carbon alloy steels, and in low carbon alloy steel the amount of γR was decreased, contrary to the case with high carbon alloy steels.

ON ALUMINIUM SLAB CASTING

(1) The CastingThe effect of Fe, Si, Cu or Mn upon casting cracks of aluminium ingots were investigated by measuring shrinkages or cracks which were found in casting into a particular metal mould (See Fig. (2)). Results obtained are as follows: There is a relationship of casting and mould temperature within a limited range which favors prevention of cracking, varying according to the kind and the content of the impurities. The higher the casting temperature, the larger the shrinkage, and so the casting at higher temperature promotes the opportunity for cracks. Cracks which were found in such cases as hindrance of free contraction, become finer by slow cooling but larger by the rapid cooling, and also the higher the purity of Al, the finer they become generally.In this experiment, the cause of cracking was assumed, in a general way, to lie in the stress due to the disparity of the solidification range of the alloy, but in practical operation, the tendency to cracking is to a marked degree affected by other factors for example, the casting technique.(2) On the Developement of the Faults in the Slab Ingots.The relation between casting techniques and cracks appearing in aluminium ingots has been studied with a practical tilting mould. These experiments were made for the purpose to find and prevent the developement of faults in aluminium ingots. The faults of the ingots were examined by means of specific gravity and hardness tests or microscopic examinations, and also the change of temperature inclination in the course of pouring.The pouring temperature and the temperature of moulds affect seriously the cracks. The rate of casting, the shape of the runner, the degree of tilting the mould, etc. also influence the cracking. Among these, it was found: when the pouring temperature is high the temperature gradient along the vertical direction becomes large, and the gradient in the neighbourhood of the gate becomes much larger than in the opposite portion, and in such a condition, cracking appears mainly on the gate side.From change of the thickness of slabs, the following formula was introduced:Hy=(2Ha+ql2)/2lx-q/2x2On the other hand, the developement of faults were identified by calculating the ratio of q to H, where the former is the force by which the slab tends to contract to the inner direction and the latter is that by which it tends to maintain the original form (See Fig. 50)