Unloaded End Research Articles

Load-deflection and surface properties of coated and conventional superelastic orthodontic archwires in conventional and metal-insert ceramic brackets

Properties of coated archwires, which have been introduced for esthetic demands during orthodontic treatments, along with the use of tooth-colored brackets, are not clear. The aim of this study is to compare the load-deflection and surface properties of coated superelastic archwires with conventional superelastic archwires in conventional and metal-insert ceramic brackets. In this experimental study, 3 types of archwires including ultraesthetic polycoated, ultraesthetic epoxyresin coated and conventional (uncoated) superelastic nickel-titanium (NiTi) archwires were used in each of 2 types of brackets including conventional and metal-insert ceramic. To simulate oral environment, all specimens were incubated in artificial saliva using thermocycling model and then were tested in three-bracket bending test machine. Loading and unloading forces, plateau gap and end load deflection point (ELDP) were recorded. Archwires were investigated with a stereomicroscope before and after the experiment. Two-way ANOVA and Tukey tests were used at P<0.05. Epoxyresin archwires produced lower forces (19 to 310 gr) compared to polycoated (61 to 359 gr) and NiTi (61 to 415 gr) (P<0.0001). The maximum ELDP (0.43 mm) was observed in epoxyresin archwires (P<0.001). Coatings of some epoxyresin wires were torn and of polycoated wires peeled off. Conventional ceramic bracket produced higher loading forces with polycoated and NiTi archwires and lower unloading forces with all 3 types of archwires compared to metal-insert type (P<0.05). Epoxyresin-coated archwire had the lowest force and highest ELDP. Coatings were not durable in these experimental conditions. Conventional ceramic bracket produced higher frictional force compared to metal-insert type.

Aesthetic nickel titanium wires--how much do they deliver?

The purpose of this study was to evaluate and compare the force levels of aesthetic Ni-Ti wires to regular Ni-Ti wires of the same dimension and evaluate their mechanical properties. Aesthetic and regular maxillary superelastic Ni-Ti wires (0.016 × 0.022) from four different manufacturers (G&H Wire Company, TP Orthodontics, GAC International, and Ortho Organizers) were selected and grouped I-IV. The loading and unloading values were compared using a three-point bending test. The unloading end values were also recorded to evaluate the recovery of archwires after each deflection. The unloading values were recorded at 0.5, 1.5, and 2.5 mm after loading deflections of 1, 2, and 3 mm, respectively. Cross-sectional scanning electron microscopy was used to assess the coating thickness of aesthetic wires. The results, statistically analysed, showed a significant decrease in force values for the aesthetic wires in groups I, III, and IV (P < 0.001) as compared to regular Ni-Ti wires of the same dimension from the same manufacturer. There was no significant difference in force values for group II wires. A statistically significant decrease in force values of epoxy-coated wires was observed in groups I, III, and IV only. This is of obvious clinical significance during wire selection. The group II coated wires, however, exhibited forces comparable to their regular Ni-ti wires with a difference that was statistically insignificant. The end values of aesthetic wires showed almost complete recovery for groups I, II, and III after 2 and 3 mm deflections.

Slip behaviour at cyclic pullout tests under transverse tension

In case of a reinforced concrete structure being exposed to bond stresses that transfer great forces, a relative displacement between reinforcing bar and concrete occurs. The slip is an important parameter in order to evaluate the quality of the bond concerning repeated pullout loads. A rapid slip increase is caused by bond weakening due to longitudinal cracks resulting from transverse tension. Within the bond area the slip is not uniformly distributed along the reinforcing bar. It is still unexplained how far fatigue and transverse tension affect the distribution. This paper focuses on the development of the slip curve under repeated loading and transverse tension. Results from cyclic pullout tests were applied and particularly the slip difference between the loaded and unloaded end of the pullout bar was investigated. It could be observed that both an increase in load cycles and transverse tension did not cause an appreciable change in slip difference.

Variable thermal loading analysis on (111) plane of single crystal gold

The temperature response on the properties of single crystal gold (111) plane at elevated temperatures was considered in this work. The ability to perform nanoindentation experiments at elevated temperatures opens up significant new possibilities in nanotechnology. The experiments are performed at various temperatures of 373 K, 473 K and 573 K with tailor made Berkovitch tip of radius 100 nm to study the behavior of single crystal gold. The new phenomenon of material bouncing back under the indenter at the end of unloading was clearly noted, due to the accumulation of high energy. The results for different temperatures were compared. Our experiments clearly show the onset of the first burst of dislocation glide, which is indicated by a sudden increase of displacement with no increase of loading, the onset of plastic deformation in connection with the periodic bursts, and the strain hardening, softening and release effects. Pile up was also observed. The complete elastic range was found. There was significant drop in the hardness, elastic modulus and the increase in depth with increasing temperature. The elastic recovery was reduced at higher temperatures.

Micromechanical behavior of granular materials with inherent anisotropy under cyclic loading using 2D DEM

This paper presents the micromechanical behavior of granular materials due to different initial inherent anisotropic conditions during cyclic loading using the discrete element method (DEM). Oval particles were used to model the samples. Three samples, with three different inherent anisotropic conditions based on the particle’s bedding direction, were prepared and subjected to biaxial cyclic loading. The differences in the inherent anisotropic conditions of the samples affect the stress–strain-dilative behavior of granular materials. The width of the stress–strain cyclic loops decreases as the preferred bedding angle changes from vertical to horizontal. Contact fabric evolution is found to be dependent on the inherent anisotropic fabric of the sample during loading and unloading. The fabric anisotropy is dominant for horizontal particle bedding at the end of loading and for vertical particle bedding at the end of unloading. A change in fabric anisotropy is observed only for the first few loading–unloading cycles for the given conditions depicted in the present study.

Analytical Method for Failure of Anchor-Grout-Concrete Anchorage due to Concrete Cone Failure and Interfacial Debonding

Depending on the relevant material properties, failure of grouted anchor anchorage to concrete can result from pullout of concrete cones, debonding at either anchor-grout or grout-concrete interface, fracture of anchor, and combination of some of these failure modes. The intention of the present study is to present an analytical method for analyzing the concrete cone failure during the process of interfacial debonding by using deformation compatibility conditions at the anchor-grout and grout-concrete interfaces. The tensile stress in the anchor and interfacial stresses at the two interfaces are formulated at different loading stages. It is assumed that interfacial debonding modeled as an interfacial shear crack only appears at the anchor-grout interface and is initiated from the loaded end. The concrete cone and interfacial debonding failures are analyzed according to the sizes and material properties of the anchorage. Three different failure modes are considered, including concrete cone failure at the unloaded end without interfacial debonding, interfacial debonding plus concrete cone failure at the same height as the interfacial shear crack tip, and interfacial debonding plus concrete cone failure at the unloaded end. In each case, the load for the initiation of the concrete cone failure, and the cone angle are determined analytically. Subsequently, material and structural parameters are adopted to study their influences on the failure modes and calculated results. It is found that if the embedment length is relatively long, the concrete cone failure occurs within a local scope. If the concrete diameter is large enough, the failure mode is the interfacial debonding without concrete cone failure. The conclusions provide useful references for engineering practice such as designing grouted anchor anchorage to concrete in light of different needs and failure modes.

Post-buckled precompressed subsonic micro-flight control actuators and surfaces

This paper describes a new class of flight control actuators using post-buckledprecompressed (PBP) piezoelectric elements to provide much improved actuatorperformance. These PBP actuator elements are modeled using basic largedeflection Euler-beam estimations accounting for laminated plate effects. Thedeflection estimations are then coupled to a high rotation kinematic model whichtranslates PBP beam bending to stabilator deflections. A test article usingPZT-5H piezoceramic sheets built into an active bender element was fitted withan elastic band which induced much improved deflection levels. Statically thebender element was capable of producing unloaded end rotations on the order of ± 2.6°. With axial compression, the end deflections were shown to increase nearly four-fold.The PBP element was then fitted with a graphite–epoxy aeroshell which wasdesigned to pitch around a tubular stainless steel main spar. Quasi-static benchtesting showed excellent correlation between theory and experiment through ± 25° of pitch deflection. Finally, wind tunnel testing was conducted at airspeeds up to 120 kts(62 m s−1,202 ft s−1). Testing showedthat deflections up to ± 20° could be maintained at even the highest flight speed. The stabilator showed no flutter ordivergence tendencies at all flight speeds. At higher deflection levels, it was shownthat a slight degradation deflection was induced by nose-down pitching momentsgenerated by separated flow conditions induced by extremely high angles of attack.

Modeling Feedback Scheme of Empty Cars in Unloading End of Heavy Haul Railway

The transportation organization of heavy haul railway is complex in China, especially, the feedback of empty cars. On the basis of reference to the existing research results, and deep analysis of the characteristics of empty cars distribution of heavy haul railway, the authors construct the feedback schematic model of empty cars in unloading end of heavy haul railway. The minimum quantity of the combined trains and the time for combination is taken as the model goal and solution algorithm on the basis of minimum cost and maximum flow is formulated. Daqin railway is taken as an example and relevant conclusions of feedback scheme of empty cars of heavy haul railway, through an analysis of calculation results, are drawn.

Bond Stresses Along Plain Steel Reinforcing Bars in Pullout Specimens

Although recent research has recognized the existence of relationships between bond stress, slip and bar force, mechanics-based analytical prediction models for bond of plain reinforcement based on pullout specimens have not yet been established. This study establishes mechanics-based relationships between bond stress, bar force, slip at the unloaded end of the bar, and slip along the length of plain steel reinforcing bars in pullout specimens. Two 200 mm (7.9 in.) diameter by 800 mm (31.5 in.) long pullout specimens reinforced with instrumented built-up hollow reinforcing bars were tested. The derived mechanics-based relationships show that bond stress is a function of relative bar slip, slip is a function of bar force, and bar force is a function of bond stress. It is shown both analytically and experimentally that bond stress magnitudes vary along the length of the bar at all applied loads. Maximum pullout resistance was observed just before slip initiated at the unloaded end of the bar, and the bond resistance subsequently reduced as slip increased. The location of the peak bond stress shifts from the loaded end toward the unloaded end of the specimen with increasing applied load. This study also demonstrates that a previously-developed theoretical two-step bond stress-slip model captures the essential features of bond behavior observed experimentally in pullout specimens once the authors accounted for the debonding adjacent to the loaded end of the specimen.

4061 ポリマーブレンドの疲労き裂進展の有限要素解析(G03-13 き裂進展(2),G03 材料力学)

The stress distribution and deformation of acrylonitrile-butadiene-styrene resin with a single edge notched specimen at the crack tip are obtained by the finite element analysis under the cyclic loading condition. At the end of unloading in one cycle, the crack surface away from the crack tip is closed. However, the surface by the crack tip is opened even though the applied stress is equal to zero. The stress at the crack tip increases with the increase the cycles like the strain hardening behaviors similar to that of metals. In addition, the position of maximum stress moves to ligament away from the crack tip and then back and passes the crack tip, and moves to the crack surface. Since the craze is caused by the tensile stress, the movement induces expanding the damage region at crack tip.

Heat Stress Facilitates the Recovery of Atrophied Soleus Muscle in Rat

Effects of heat stress on the recovery of atrophied soleus muscle were studied in rats. Ten-week-old male Wistar rats were randomly divided into cage control (CC) and 5-day hindlimb suspension group (HS). The half of the rats in group HS was exposed to heat stress (41 degrees C for 60 min) in an incubator immediately after the hindlimb suspension (HS-H) and the other group of rats was not heat stressed (HS-C) prior to 10 days of ambulation recovery. One group of cage control rats (CH) was also exposed to heat similarly. The soleus muscles were dissected at four time points, i.e., immediately after the suspension (or heat stress), and 3, 5, and 10 days after the recovery (n=8 per group at each time point). The absolute wet weight and water and protein content of whole soleus muscle in group HS-C were approximately 36, 27, and 8 mg less than CC (p <0.05). Thus, the percentage contribution of water and protein loss to the decrease in muscle weight was 75 and 22%, respectively. Although water content, as well as muscle weight, was elevated within 3 days, the increase of protein was delayed. Heat exposure prior to recovery accelerated the increase in protein content even in the control group. These phenomena were closely associated with 72-kD heat shock protein (HSP72) content. It is suggested that heat stress applied at the end of hindlimb unloading facilitated the recovery of atrophied soleus muscle of rat, through possibly HSP72-related events of protein metabolism. The data also indicated that the combination of heat and mechanical stress evoked larger and long lasting HSP72 response than does heat or mechanical stress alone.

Crack initiation and Extension Characteristics of Ceramic/Metal Joint under Cyclic Loading.

Crack initiation and extension characteristics of tension side, view side and compression side of ceramic/metal joints were investigated under cyclic bending loading. Location of cracks and propagations were investigated by SEM and X-ray compositional analysis methods. The stress and strain distribution under cyclic bending loading were investigated by FEM analysis. The results obtained are as follows. (1) Crack initiation occurred at ceramic/interlayer interface at the specimen corner under cyclic bending loading. The unstable fracture occurred from the interface crack. At the 84∼90% of mean strength, crack initiated at ceramic/interlayer interface at the specimen corner. (2) After a main crack occurred many microcracks appeared in order near the main crack region with the increase of maximum stress. Finally they united to the main crack under cyclic loading. The length of crack was increased with increasing maximum stress. The curve slopes of crack lengths versus stresses also increased with increasing maximum stress. Under constant cyclic bending loading, the cracks intermittently grew. (3) At compression side, when the absolute value of maximum stresses were higher than those of tension side, cracks started on the ceramic/interlayer interface and grew up to about 40μm, and finally halted. (4) The crack initiations occurred at the ceramic/brazing filler interface. The location of crack initiation under cyclic bending loading was same as monotonic strength. (5) The crack length increment was decelerated with increasing energy release rate, then increased. The difference of the relationship between crack length increment and energy release rate was less than that of crack length increment and maximum stress. (6) From the FEM analysis, the plastic deformation progressed in interlayer when specimen was loaded and the plastic strain of interlayer left when unloaded. In the interlayer of interface, as compressional plastic strain was constrained by materials around it, tensile residual stresses occured at the compression side at end of unloading. That is why crack initiation occurred in the compression side.

Modernization of the electric furnace SKZ-8.40.1/9

1. To eliminate chilling at the unloading end of electric conveyor furnaces for heat treatment, it is recommended to change the design of the heaters in the third zone of the furnace and to arrange for separate voltage supply to the end heaters via a transformer. This increases the productivity of the furnaces by 10% and cuts down on rejects. 2. Using accurate calculation methods in analyzing the operation of complex units of electric furnaces is a reserve for raising their productivity.

A Photoelastic Approach to Transient Stress Problems Employing Low-Modulus Materials

Abstract The objective of the program discussed in this paper was to develop a method, using photoelasticity and low-modulus materials, for studying dynamic stress distributions. Early in the program a number of low-modulus materials were studied and Hysol 8705 (a urethane-rubber compound) was selected as the most promising. A complete study of its mechanical and optical properties was made under static and dynamic loadings. It was established, that Poisson’s ratio ν is independent of rate of loading, the stress fringe value fσ is independent of rate of loading for strain rates greater than 8 in/in/ sec, and both the modulus of elasticity E and the strain fringe value fϵ were dependent oil the rate of loading. The specific energy loss for the material was about 10 per cent for the stress ranges associated with photoelastic determinations. Experimental observations of photoelastic fringe patterns in a rectangular strut subjected to axial impact were made to illustrate the potential of the method. Three different end conditions were imposed on the unloaded end of the strut: (a) A free end normal to the axis; (b) a fixed end normal to the axis; and (c) a free end inclined 45 deg to the axis. For the cases where the ends were normal to the axis it was found that the fringes followed the same law of reflection as the law for stresses given by elementary wave theory.