Flat Shoulder Research Articles

Effect of re-filling probe hole on tensile failure and fatigue behaviour of friction stir spot welded joints in Al–Mg–Si alloy

In this study, the fatigue behaviour of Al–Mg–Si aluminium alloy joints joined by friction stir spot welding (FSSW) was investigated. FSSW was performed using a specially designed double-acting tool consisting of outer flat shoulder and inner retractable probe, which could re-fill probe hole of the joints. Lap-shear specimens with probe hole and re-filled one were fabricated. The tensile strength of the joint with re-filled hole was higher than that of the joint with probe hole, where shear fracture through the nugget occurred in both joints. The re-filling process increased effective cross sectional area of the nugget, resulting in higher tensile strength. Fatigue tests were conducted using lap-shear specimens at a stress ratio of R = 0.1. The fatigue strength of the joint with re-filled probe hole was nearly the same as, but lower than, at low and high applied loads, respectively, that of the joint with probe hole. The pull out of the nugget, i.e., plug type fracture, was seen in the joint with re-filled probe hole, while shear fracture through the nugget was observed in the joint with prove hole. The observation of fatigue crack growth path revealed that the plug type fracture through the upper sheet was responsible for the observed lower fatigue strength of the joint with re-filled prove hole at high applied loads.

Microtensile bond strength between crown and root dentin and two adhesive systems

Since bonding agent effectiveness is usually evaluated on coronal substrates, available knowledge for judging the effectiveness of bonds to root dentin is insufficient. The objective of this study was to evaluate the bond strength of 2 adhesive systems to crown, cervical finish line, and post space dentin. Twenty bovine maxillary incisors were used in this study. Teeth were sectioned along the cemento-enamel junction using a low-speed diamond blade to separate the crowns and roots. Then the crowns and roots were each divided into 2 groups, according to the 2 adhesive systems tested (n=10). The facial enamel surfaces of the crowns were abraded with 600-grit silicon carbide paper to expose flat, midcoronal dentin surfaces. Drills and a diamond rotary cutting instrument were used in a low-speed handpiece to prepare post spaces in the root canals. The same diamond rotary instrument was used to prepare horizontally flat surfaces in the cervical areas, similar to the horizontal aspect of a shoulder finish line. Composite resin was placed incrementally into the post spaces, over the flat cervical shoulder areas, and on the coronal dentin. Bonded beam specimens (0.5 mm(2) of cross-sectional area) derived from crown, cervical finish line, and post space dentin, were prepared for microtensile bond testing and tested in tension. Data were analyzed using 2-way ANOVA and Tukey post hoc test (alpha=.05). Failure patterns of tested specimens were analyzed using scanning electron microscopy. The mean tensile bond strength values (SD) (MPa) were: Single Bond-crown: 29.8 (4.0); Single Bond-finish line: 18.7 (4.3); Single Bond-post space: 17.0 (4.8); Clearfil SE Bond-crown: 30.1 (6.4); Clearfil SE Bond-finish line: 30.4 (5.3); and Clearfil SE Bond-post space: 17.0 (4.2). Bond strengths to post space dentin were lower than those to coronal dentin for both adhesives (P<.001). However, no significant difference was observed between coronal and finish line dentin for Clearfil SE Bond. Bond strength was reduced when adhesives were used in bonding to post space dentin. Cervical finish line sites bonded using Clearfil SE Bond adhesive yielded bond strength similar to that of coronal dentin sites.

In vitro fracture resistance of posterior metal-ceramic and all-ceramic inlay-retained resin-bonded fixed partial dentures

Inlay-retained resin-bonded fixed partial dentures (RBFPDs) are conservative prosthetic restorations; however, their resistance to fracture is not clear. The purpose of this study was to compare fracture loads of posterior complete coverage metal-ceramic restorations with all-ceramic inlay-retained RBFPDs. Thirty-two posterior ceramic RBFPD restorations were divided into 4 groups (n=8): (1) Complete metal-ceramic fixed partial dentures (MC-FPDs) fabricated of Ni-Cr-based alloy (Wirolloy) and veneered with a ceramic (IPS d.SIGN) as the control group; (2) inlay-retained metal-ceramic (MC RBFPDs) with the same materials as the control; (3) inlay-retained lithium disilicate (LD) glass-ceramic (IPS Empress 2) RBFPDs; and (4) inlay-retained zirconia-based (Z) ceramic (Cercon) RBFPDs. Control specimens were prepared to receive conventional complete MC-FPDs designed to include a 1.3-mm-circumferential, 90-degree flat shoulder with rounded angles. Inlay-retained RBFPD specimens were prepared with 2-mm occlusal reduction but without bevels at the occlusal or gingival margins. Specimens were loaded and fracture loads (N) measured at fracture with a universal testing machine at a crosshead speed of 1.0 mm/min and 250 kgf load cell. Data were analyzed with 1-way ANOVA and Duncan test (alpha=.001). Fracture loads (mean +/- SD) were greatest for control specimens (1318.43 +/- 211.00 N) and Z-RBFPD (1247.70 +/- 262.51 N) specimens as compared to MC-RBFPD or LD-RBFPD (P < .001). MC-RBFPD exhibited the next highest fracture loads (958.01 +/- 194.29 N), and LD-RBFPD exhibited the significantly lowest values (303.23 +/- 92.54 N) of the materials tested (P < .001). Inlay-retained zirconia-based ceramic RBFPDs demonstrated the greatest fracture resistance among all inlay-retained restorations tested.

Mixed-mode fatigue crack propagation in thin T-sections under plane stress

Data that can be used in the fatigue analysis of flat T-section bars subjected to axial loading and local restraint are presented. The paper describes how finite element analysis has been used to obtain stress fields in the vicinity of a crack or crack-like flaw introduced into the fillet (i.e. high-stress) region of the component. The effect of both the position and inclination of the crack has been investigated. The inclination of the crack to the transverse direction is varied in such a way that a combination of mode I (tension opening) and mode II (in-plane shear) crack tip conditions are created in the component when subjected to axial loading which is applied to the entire flat shoulder of the projection. Linear elastic fracture mechanics finite element analyses have been performed, and the results are presented in the form of J integrals and notch and crack configuration factors for a wide range of component and crack geometric parameters. These parameters are chosen to be representative of typical practical situations and have been determined from evidence presented in the open literature. The extensive range of notch and crack configuration factors obtained from the analyses are then used to obtain equivalent prediction equations using a statistical multiple non-linear regression model. The accuracy of this model is measured using a multiple coefficient of determination, R2, where 0 &lt; R2 &lt; 1. This coefficient is found to be greater than or equal to 0.98 for all cases considered in this study, demonstrating the quality of the model fit to the data. Predictive equations for stress intensity factors and J-integral values, which are based on the elastic stress concentration factor, are also developed. A crack propagation methodology, based on existing theory coupled with these predictive equations, is then presented for this type of component and loading.

Tungsten–tellurite glass: a new candidate medium for Yb 3+-doping

Yb 3+-doped tungsten–tellurite glasses with compositions of (50–70)TeO 2–(30–10)WO 3–20Li 2O, (80–90)TeO 2–(10–0)WO 3–10BaO, (65–75)TeO 2–(25–15)WO 3–10La 2O 3, (55–65)TeO 2–(35–25)WO 3–10Bi 2O 3 and (80–85)TeO 2–(10–5)WO 3–10Nb 2O 5 (mol%) have been prepared. Thermal stability and spectroscopic properties of Yb 3+-doped ternary tungsten–tellurite glasses have been measured. Yb 3+-doped La 2O 3- and Nb 2O 5-containing ternary tungsten–tellurite glasses possess the difference between the glass transition temperature ( T g) and the onset crystallization temperature (T x ), ΔT (=T x −T g )>160 °C, a flat absorption shoulder located between 940 and 960 nm region with absorption cross-sections >0.5×10 −20 cm 2, secondary emission cross-sections (at ∼1.02 μm)>0.7×10 −20 cm 2, and the ratios of secondary-to-primary peak emission cross-sections, σ s/ σ p>70%, respectively.

Crown margin design: A dental school survey

A survey of dental schools in the United States and Puerto Rico was conducted concerning ceramometal crown margin design. The crown margin designs taught most often were the flat shoulder, the 45-degree bevel shoulder, and the chamfer.

Thermodynamic properties of molten Na‐Te solutions

AbstractThermodynamic properties of liquid Na‐Te solutions were measured over the range 0–52 at.% Na at temperatures between 573 and 873 K by means of alloy concentration cells. Beta alumina was used as the solid electrolyte. The following properties were derived from the emf data: ΔG, ΔH, ΔS, the excess heat capacity CE p and the excess stability, ES. The Gibbs energy, enthalpy and entropy showed marked negative deviations. The plot of excess stability versus composition exhibits a rather flat shoulder between 10 and 20 at.% Na and a broad maximum or shoulder near 50% Na indicating maximum short‐range ordering near these compositions. Liquidus and invariant points on the phase diagram as well as the Gibbs energies of formation of the solid compounds NaTe3, NaTe and Na2Te have also been determined.

Mixtures of alkanes with polar molecules showing internal rotation: an unusual composition dependence of C pE of 1,2-dichloroethane + an n-alkane

Excess molar volumes V E at 298.15 K have been determined as a function of mole fraction x for several mixtures belonging to the series 1,2 – dichloroethane (1,2 – C 2H 4Cℓ 2) + an n-alkane (n-C ℓH 2ℓ+2), ℓ = 7,10,14,16. The instrument used was a vibrating-tube densimeter. For the same mixtures and at the same temperature, a Picker flow calorimeter was used to measure excess molar heat capacities C p E at constant pressure. V E is positive for all systems, with V E (x 1 = 0.5 amounting to 0.918 cm 3.mol −1 for x 1 1,2-C 2H 4Cℓ 2 + x 2n-C 7H 16 , and to 1.622 cm 3 mol −1 for x 11,2-C 2H 4Cℓ 2 + x 2n-C 16H 34. The results on C p E are strikingly unusual in that for ℓ = 7 a deep minimum is observed at x 1 ≈ 0.3, and a pronounced, rather flat shoulder (almost a second minimum) around x 1 ≈ 0.75. With increasing ℓ, C p E (x 1,min) becomes more negative and concomitantly the shoulder less prominent. This behavior is reminiscent of the shapes of C p E(x 1) reported by Wilhelm (1979a) for mixtures of 1,2 – C 2H 4Cℓ 2 with cyclohexane and methylcyclohexane, and – most interestingly – by Grolier (1984) and Inglese (1982, 1984) for mixture of cyclic diethers with n-alkanes and cyclohexane.

Thermal death of a hydrocarbon bacterium in a nonaqueous fluid.

A hydrocarbon-utilizing Brevibacterium which grew into the oil phase of an oil-water system was tested for survival at elevated temperature. Cells suspended in oil and cells that had been resuspended in aqueous solution were tested by placing 1-ml samples of the cell suspension in small test tubes immersed in a controlled-temperature water bath. The resultant survival curves in oil consisted of two parts, a flat shoulder obtained in the first half of the heating period, followed by a break indicating rapid die-off. The break in the curves occurred after 50% of the cells were killed. This occurred at exposures of 25, 15, and 8 min for 78, 88.6, and 96.2 C, respectively. The survival curve for 63.5 C in the aqueous solution was a rapid, exponential die-off. The actual increase in survival of the organism in oil is reflected by the length of the shoulder portion. The shoulder occurs only in an oil medium and is increased by decreasing temperature and increasing age of the culture.

The survival of Micrococcus radiodurans irradiated at high LET and the effect of acridine orange.

SummaryThe radiation survival curve of Micrococcus radiodurans consists of a long flat shoulder, followed by an exponential part. When acridine orange is added to the growth medium after irradiation, the shoulder is reduced without changing the final slope. A method is described whereby a measure of repair is obtained from the length of shoulder, and a measure of unrepaired damage from the final slope. With changing LET, these two features of the curve differ. The final slope has a definite optimum LET for maximum sensitivity at a value very near to that for yeast and higher organisms. The length of the shoulder steadily increases as LET increases, suggesting that the target for inactivating the repair mechanism is different from the lethal target.

Photon-Induced Reactions

A detailed derivation is given of the Breit-Wigner formula for the case where one particle is a photon. The half-width ${\ensuremath{\Gamma}}_{\ensuremath{\gamma}}$ is found to have all the qualitative properties of a heavy particle half-width: It is proportional to the level spacing $D$ and to $X{P}_{l}(X)$ where $X=\ensuremath{\kappa}R$ and ${P}_{l}$ is the penetration probability for an uncharged particle. ${\ensuremath{\Gamma}}_{\ensuremath{\gamma}}$ also depends explicitly on the details of the many-particle structure of the compound state, so that single-particle estimates of ${\ensuremath{\Gamma}}_{\ensuremath{\gamma}}$ appear to be of limited applicability.The formulas are applied to recent $\ensuremath{\gamma}\ensuremath{-}n$ measurements on ${\mathrm{O}}^{16}$, ${\mathrm{N}}^{14}$, and ${\mathrm{F}}^{19}$. The breaks in the ${\mathrm{O}}^{16}$ excitation curve are due to resonances in ${\mathrm{O}}^{16}$, except for the threshold, which presumably does not represent a resonance. At higher energies the giant $\ensuremath{\gamma}\ensuremath{-}n$ electric dipole resonances are interpreted as indicating a certain "coherence" in the motion of the compound state, classically represented as countercurrent neutrons and protons. It is suggested that a flat shoulder in the excitation curves below the giant resonance may represent incoherent electric dipole excitation rather than coherent magnetic dipole and electric quadrupole excitation. The matrix elements necessary to fit the measured magnitudes are surprisingly large, which suggests that the one-particle wave functions have quite similar shapes in the ground state and in highly excited states.

A Dead Sea Scroll Jar at the Oriental Institute

The Oriental Institute of the University of Chicago has recently acquired by purchase from the Jordan Government, through the cooperation of Mr. G. Lankester Harding of the Jordan Department of Antiquities, one of the jars from the Scroll Cave near 'Ain Feshkha.' The jar, complete with cover, had been assembled from over one hundred fragments at the Palestine Archaeological Muiseum under the supervision of Mr. Harding and Pare R. de Vaux (O. P.) of the ecole Biblique, and was dispatched to the United States by air freight in October, 1950, with the courteous assistance of Fr. Roland Murphy (O. Carm.), then Fellow at the American School at Jerusalem. It was lost in transit, located with the assistance of Prof. A. H. Detweiler of Cornell University in the course of a visit to the Jerusalem School in January 1951 and arrived at Chicago a month later in its original packing but sadly in need of repair because not a few of the joins had come apart in shipment. Reassembled by the Institute's preparator, Mr. Robert Hanson, the jar itself (not counting the lid) has a height of 71.7 cm., a maximum diameter of 4.7 cm. and a maximum circumference of roughly 79 cm. Its large tubular body is set upon a low base only 13.1 cm. in diameter and slightly concave in shape, and is constricted at the top by a flat shoulder that ends in an abbreviated neck with an opening 16.5 cm. across. The diameter of the mouth thus exceeds that of the base and for reasons that should be obvious. Though an element of unevenness in the surface of the shoulder precludes a tight fit, there can be no doubt that the accompanying bowl-shaped lid was of a type intended to cover the mouth of jars of this kind, matching the jar in ware, fitting nicely over the neck and reproducing in inverted form and on a smaller diarmeter the base and the first few centimeters of the body of the jar itself. The lid arbitrarily assigned to the Chicago jar has a height of 6.4 cm. and a diameter of 18.7 cm. Its circumference is 59 cm. At the top it ends in what is really an inverted base 7.5 cm. across, the transition from base to bowl-shaped body being made by a shallow trough exactly fitting the finger-tips of a hand taking hold of it. The ware is well-levigated reddish clay covered with a slip that has flaked off in many areas; it is now of a dirty creamy color and may originally have been somewhat darker. The color of the ware itself is fresh and clearly visible along the edges of the fragments, both those still in place as assembled at Jerusalem and those reset at Chicago, showing that the jar had been smashed only recently arid not in antiquity, perhaps when the illicit search for additional manuscripts was conducted in the Cave shortly before its excavation. The body of the jar reflects in the unevenness of its surface the method of its construction, a suc-