Study of Bismuth Telluride Crystal Strength

The article presents results of strength tests of bismuth telluride prismatic samples obtained by growing crystals. These crystals have semiconductor properties and are used in the heat machines, the run-ability of which largely depends on the strength of crystals. Data available in the literature are significantly different from each other. It has been shown that, the most consistent strength tests results are obtained in case of bend testing. The measurement results of the elasticity modulus and tensile strength are given. For tests, an INSTRON testing machine with maximum direct stress of the 1000 H was used.

High Strain-Rate Compressive Properties of Carbon/Epoxy Laminated Composites – Effects of loading direction and temperature

The high strain-rate compressive characteristics of a cross-ply carbon/epoxy laminated composite in the three principal material directions or fibre (1-), in-plane transverse (2-) and throughthickness (3-) directions are investigated on the conventional split Hopkinson pressure bar (SHPB) over a range of temperatures between 20 and 80 °C. A nearly 10 mm thick cross-ply carbon/epoxy composite laminate fabricated using vacuum assisted resin transfer molding (VaRTM) was tested. Cylindrical specimens with a slenderness ratio (= length/diameter) of 0.5 are used in high strain-rate tests, and those with the slenderness ratios of 1.0 and 1.5 are used in low and intermediate strain-rate tests. The uniaxial compressive stress-strain curves up to failure at quasi-static and intermediate strain rates are measured on an Instron testing machine at elevated temperatures. A pair of steel rings is attached to both ends of the cylindrical specimens to prevent premature end crushing in the 1-and 2-direction tests on the Instron testing machine. It is shown that the ultimate compressive strength (or failure stress) exhibits positive strainrate effects and negative temperature ones over a strain-rate range of 10–3 to 103/s and a temperature range of 20 to 80 °C in the three principal material directions.

Deformation of EPS Foam Under Combined Compression-Shear Loading: Experimental and Computational Analysis

Expanded Polystyrene (EPS) foam material is widely used as an energy absorption engineering material. Its compression behaviour, both quasi-statically and dynamically, has been studied widely. However, its mechanical behaviour under combined compression-shear loading is poorly understood due to the difficulty of performing such tests. A novel test rig is presented to perform combined compression-shear loading tests in quasi-static loading conditions. Different densities of EPS foam were tested with this apparatus using a universal Instron testing machine. The compressive and shear stresses were obtained and compared, the results show that the shear stress at yield of EPS foam under combined compression-shear loading is much lower compared with the compressive stress at yield. On the other side, the compressive stress at yield can as high as 40% lower compared with pure compression. The FEA simulations were performed using the Abaqus/explicit 6.14 code and it is found the numerical predictions and experimental results agree closely, which indicates that our FE models exhibit good reliability in predicting the response of EPS foam under such loading conditions.

Effect of Metal Extension of Crown in the Screw Access Channel of a Posterior Implant Abutment on the Retention of Cement Retained Prosthesis

Purpose: Reducing the height of the implant abutment due to limited interarch space decreases the surface area for retention of cemented restorations. The purpose of this in vitro study was to see whether engaging the screw access channel with metal extension compensates for the loss of retention of posterior crowns cemented on shorter abutments. Material and Methods: Four identical prefabricated abutments were mounted on implant replicas embedded in acrylic resin blocks. Three of these abutments were reduced in height by 1 mm, 2 mm, and 3 mm respectively and one was left unmodified. Two sets of base metal crowns were fabricated for each abutment, one without and one with the metal extension inside the screw access channel. The crowns were cemented using Tempbond NE. The tensile forces required to separate the cemented crowns from abutments were measured using an Instron testing machine. Statistical analysis of the data was performed using a 2-way analysis of variance and Fisher's protected least significant difference at 0.05 level of significance. Results: An increase of 24% to 261% in retentive forces was observed for the group having metal extension in the screw access channel. Statistically significant differences (P < .001) were found among 2 types of crowns and four heights of abutments. Generally, the retentive forces were reduced in magnitude as the abutment height was reduced. Conclusion: The retention of a casting cemented to posterior implant abutments is influenced by the height of the abutment and the metal extension engaging the screw access channel. The crowns made with a metal extension showed superior retention values.

Comparison of the Initial Repeated Bond Strength among Three Orthodontic Bonding Systems

One of the problems that often occurred during orthodontic treatment is bracket failure. This is usually the result either of the patient’s accidentally, applying inappropriate forces to the bracket or of a poor bonding technique. Thus, a significant number of teeth have to be rebonded in an orthodontic practice. Objective: The aim of this study was to evaluate the in vitro initial repeated shear bond strength of the three adhesive systems at two and five minutes after placement of a bracket. Materials and Methods: The three bonding agent adhesives are System1+, Rely-a-bond, Unite. Two hundred and forty human premolar teeth were divided into two groups, a control and an experimental group. Each group was further divided into three subgroups for bonding brackets with the three different adhesives. Only the teeth in the experimental group were sequentially bonded and debonded two times with the same adhesive. The teeth in control and experimental groups were tested for shear bond strength (at two and five minutes after the bracket was bonded) with an Instron testing machine. Results: The studies were found that : (1) there were differences between the shear bond strength of each adhesive in the control and experimental group. Unite had the highest shear bond strength followed by Rely-a-bond and System1+ at two minutes and five minutes, (2) the experiment group ( rebonded brackets) had higher shear bond strength than control group and Unite had in significant difference (p<0.05) of initial repeated bond strength with System1+ and Rely-a-bond at two minutes and five minutes and (3) there were mostly significant difference (p<0.05) between repeated shear bond strength at two minutes and repeated shear bond strength at five minutes. Conclusion: There were significant difference of the initial repeated shear bond strength of each adhesive. The orthodontists should be aware of applying force for tooth movement into the repeated bonding brackets.

Effects of physical and morphological properties of roots on fracture resistance

ABSTRACT Objective: The aim of this study was to determine how physical and morphological properties affect the fracture resistance of roots, and which criteria are important for root specimen standardization in fracture resistance studies. Materials and Methods: Seventy-five freshly extracted human canine teeth were selected. Crowns were sectioned from the cement–enamel junction and the root lengths were set at 16 mm. Then they were prepared up to ProTaper F3 file. Each root was numbered and data were obtained by measuring mesiodistal and buccolingual dimensions, volume, weight, and density. Tests for fracture strength were performed using an Instron Testing Machine (Instron Corp. MA, USA). The force was applied axially, angled at 45 degrees with a constant speed of 1 mm/min. For each sample, the force at the time of fracture was recorded in Newtons. Results were evaluated statistically using linear regression analysis. Results: Volume and weight of the roots had more effect than mesiodistal or buccolingual dimensions on root fracture resistance. Conclusions: In root fracture resistance studies, volume or weight of the roots must be standardized when distributing roots to groups.

Assessing the effect of Alnus roots on hillslope stability in order to use in soil bioengineering

The role of plant roots in stabilizing slopes is obvious, but the amount of the effect is varied in different species. The purpose of this study was to evaluate the effect of alder (Alnus subcordata) roots on hillslope stability. The profile trenching method was used to obtain root characteristics and a standard Instron testing machine was used for determining the tensile strength of roots. Direct shear test with undisturbed samples was used for determining the soil strength parameters. Using the results of biotechnical characteristics and the Wu model, the reinforcement effect was calculated. Using the reinforcement values and soil strength parameters and Slip4Ex program, factor of safety with and without vegetation was calculated. The obtained results indicated that the root density and number of roots decreased with increasing depth and the average root area ratio was 0.071% ± 0.01. Tensile strength decreased with increasing diameter of roots following the power function with an average of 16.29 ± 3.10 MPa. The minimum and maximum of reinforcement were 0.55 KPa and 110.76 KPa, respectively. The results of this paper augment the knowledge about biotechnical characteristics of root systems of Alder species and indicate that this species increases the factor of safety about 16.79%.

Antibacterial and mechanical properties of propolis added to glass ionomer cement

ABSTRACTObjective:To investigate whether adding ethanolic extracts of propolis (EEP) might influence the antibacterial and mechanical (shear-peel band strength [SPBS]) properties of conventional glass ionomer cement (GIC) used in orthodontic band cementation.Materials and Methods:The cement was divided into four groups: one using the original composition and three with 10%, 25%, and 50% EEP added to the liquid and then manipulated. An antimicrobial assay, broth-dilution method was used to determine the antibacterial capacity of the GIC containing EEP. Eighty teeth were used for the mechanical assay, and an Instron testing machine was used to evaluate the SPBS. Kolmogorov-Smirnov and Kruskal-Wallis tests were used for statistical analyses.Results:GIC with the addition of 25% and 50% EEP activated inhibition of Streptococcus mutans (ATCC 25175) growth, but this effect did not occur in the group to which 10% EEP was added or in the control GIC group. There was no significant difference between the groups in terms of SPBS (P &gt; .05).Conclusions:The addition of EEP may increase antibacterial properties without negatively modifying the mechanical properties of conventional GIC.

Fracture Strength of Three All-Ceramic Systems: Top-Ceram compared with IPS-Empress and In-Ceram

ABSTRACT Purpose The purpose of this study was to investigate the fracture loads and mode of failure of all-ceramic crowns fabricated using Top-Ceram and compare it with all-ceramic crowns fabricated from well-established systems: IPS-Empress II, In-Ceram. Materials and methods Thirty all-ceramic crowns were fabricated; 10 IPS-Empress II, 10 In-Ceram alumina and 10 Top-Ceram. Instron testing machine was used to measure the loads required to introduce fracture of each crown. Results Mean fracture load for In-Ceram alumina [941.8 (± 221.66) N] was significantly (p < 0.05) higher than those of Top-Ceram and IPS-Empress II. There was no statistically significant difference between Top-Ceram and IPS-Empress II mean fracture loads; 696.20 (+222.20) and 534 (+110.84) N respectively. Core fracture pattern was highest seen in Top- Ceram specimens. How to cite this article Quran AF, Haj-Ali R. Fracture Strength of Three All-Ceramic Systems: Top-Ceram Compared with IPSEmpress and In-Ceram. J Contemp Dent Pract 2012;13(2): 210-215.

Use of Microcrystalline Cellulose Prepared from Cotton Fabric Waste to Prepare Poly(butylene succinate) Composites

The mechanical properties, thermal behaviors and morphology of poly(butylene succinate) (PBS)/microcrystalline cellulose (MCC) composites were investigated. The MCC used in this study was prepared by hydrolyzing cotton fabric waste with 2.5 N hydrochloric acid at 100°C for 30 min. PBS was melt mixed with three loading of MCC (10, 20 and 30 wt%) in an internal mixer, followed by compression molding into 0.3-mm sheet. The effects of MCC on the tensile properties, thermal stability, crystallization and morphology were investigated using the Instron testing machine, thermogravimetric analyzer, differential scanning calorimeter and scanning electron microscope, respectively. The incorporation of MCC into PBS results in a significant increase in the Young’s modulus but a decrease in the tensile strength and elongation at break. Moreover, the thermal degradation of the composites was not improved after introducing MCC into PBS. It was also found that, the MCC did not affect the melting temperature, but induced a slight increase in the crystallization temperature of the composites. The SEM micrographs show brittle fracture surfaces of the composites where the pull out MCC particles and pull out holes were observed.