Fracture Strength Values Research Articles

Comparative study of the mechanical properties of fiber‐reinforced denture base resin

AbstractPoly(methyl methacrylate) (PMMA) is used for removable prostheses. However, PMMA denture base resin does not meet all the mechanical requirements of prostheses. The aim of this in vitro study was to compare the transverse strength, modulus of elasticity, and impact strength values of nonreinforced heat‐polymerized and microwave‐polymerized denture base resin with those of denture base resin reinforced with continuous unidirectional E‐glass, woven E‐glass, and ultrahigh‐molecular‐weight polyethylene fibers. The mechanical properties of polymer reinforced with polyethylene fibers showed no significant increase in flexural properties. However, reinforcement with Stick fiber improved the mechanical properties. The test specimens that expressed low fracture strength values showed void spaces inside the test specimens. © 2009 Wiley Periodicals, Inc. J Appl Polym, 2009

Influence of intraradicular post and crown ferrule on the fracture strength of endodontically treated teeth

The aim of this study was to investigate the fracture strength of endodontically treated teeth restored with different posts and variable ferrule heights. Sixty freshly extracted human canines were treated endodontically and randomly assigned to 6 groups (n=10), being restored with custom-made cast post-and-core (CP0 and CP3 groups), prefabricated post and composite resin core (PF0 and PF3 groups), and composite resin (CR0 and CR3 groups). The CP0, PF0 and CR0 groups presented no ferrule and the CP3, PF3 and CR3 presented 3 mm of coronal structure. All teeth were restored with full metal crowns. The fracture strength was measured in a universal testing machine at 45 degrees to the long axis of the tooth until failure. Data were analyzed statistically by 2-way ANOVA and Tukey's test (alpha=0.05). When the mean fracture strength values were compared (CP0 group - 820.20 N, CP3 group - 1179.12 N; PF0 group - 561.05 N; PF3 group - 906.79 N; CR0 group - 297.84 N; and CR3 group - 1135.15 N) there was statistically significant among the groups (p<0.05), except for the three groups with 3 mm of coronal remaining, which were similar to each other. The results of this study showed that the ferrule in crowns promoted significantly higher fracture strength in the endodontically treated teeth.

Bulge testing and fracture properties of plasma-enhanced chemical vapor deposited silicon nitride thin films

The mechanical properties and fracture behavior of silicon nitride (SiN x ) thin film fabricated by plasma-enhanced chemical vapor deposition is reported. Plane-strain moduli, prestresses, and fracture strengths of silicon nitride thin films deposited both on a bare Si substrate and on a thermally oxidized Si substrate were extracted using bulge testing combined with a refined load-deflection model of long rectangular membranes. The plane-strain moduli and prestresses of SiN x thin films have little dependence on the substrates, that is, for the bare Si substrate, they are 133 ± 19 GPa and 178 ± 22 MPa, respectively, while for the thermally oxidized substrate, they are 140 ± 26 GPa and 194 ± 34 MPa, respectively. However, the fracture strength values of SiN x films grown on the two substrates are quite different, i.e., 1.53 ± 0.33 GPa and 3.08 ± 0.79 GPa for the bare Si substrate and the oxidized Si substrate, respectively. The reference stresses were computed by integrating the local stress of the membrane at the fracture over the edge, surface, and volume of the specimens and fitted with the Weibull distribution function. For SiN x thin film produced on the bare Si substrate, the volume integration gave a significantly better agreement between data and model, implying that the volume flaws are the dominant fracture origin. For SiN x thin film grown on the oxidized Si substrate, the fit quality of surface and edge integration was significantly better than the volume integration, and the dominant surface and edge flaws could be caused by buffered HF attacking the SiN x layer during SiO 2 removal.

Fracture strength of different soldered and welded orthodontic joining configurations with and without filling material

The aim of this study was to compare the mechanical strength of different joints made by conventional brazing, TIG and laser welding with and without filling material. Five standardized joining configurations of orthodontic wire in spring hard quality were used: round, cross, 3 mm length, 9 mm length and 7 mm to orthodontic band. The joints were made by five different methods: brazing, tungsten inert gas (TIG) and laser welding with and without filling material. For the original orthodontic wire and for each kind of joint configuration or connecting method 10 specimens were carefully produced, totalizing 240. The fracture strengths were measured with a universal testing machine (Zwick 005). Data were analyzed by ANOVA (p=0.05) and Bonferroni post hoc test (p=0.05). In all cases, brazing joints were ruptured on a low level of fracture strength (186-407 N). Significant differences between brazing and TIG or laser welding (p<0.05, Bonferroni post hoc test) were found in each joint configuration. The highest fracture strength means were observed for laser welding with filling material and 3 mm joint length (998 N). Using filling materials, there was a clear tendency to higher mean values of fracture strength in TIG and laser welding. However, statistically significant differences were found only in the 9-mm long joints (p<0.05, Bonferroni post hoc test). In conclusion, the fracture strength of welded joints was positively influenced by the additional use of filling material. TIG welding was comparable to laser welding except for the impossibility of joining orthodontic wire with orthodontic band.

Service life prediction for refractory materials

Ultrasonic pulse velocity testing and image analysis were used to predict the thermal stability of cordierite–mullite refractories. Two compositions used as substrates in fast firing of porcelain whiteware, characterized by different microstructure and crack propagation behavior, were investigated. Fracture strength and fracture toughness values were obtained from three point bending test and chevron notched specimen technique, respectively. The measurement of the ultrasonic velocity was used to assess the material degradation with increasing number of thermal-shock cycles and specimen damage was monitored using image analysis to obtain further evidence of material degradation. The correlation between thermo-mechanical properties, ultrasonic velocity, microstructure, crack-propagation behavior and thermal-shock resistance was discussed. A remarkable similarity was found between the variation of ultrasonic velocity (when measured through the length of the refractory plates) and fracture strength with number of thermal shock cycles. On the other hand, the development of surface microcracking, as monitored by image analysis, is in good agreement with the variation of KIC with the number of thermal-shock cycles. The variation of the \(\frac{d\sigma_{\rm f}}{dE_{\rm dyn}}\) ratio with number of thermal-shock cycles shows the highest gradient of the investigated trends and it is proposed as a promising parameter to differentiate refractory materials regarding their different thermal shock behavior. Service life prediction models for refractory plates, from measured values of ultrasonic velocity and surface damage analysis, were proposed and validated.

Fracture behaviour of zirconia ceramic cantilever fixed dental prostheses in vitro

Objective. Evaluation of the fracture resistance of all-ceramic cantilever fixed dental prostheses (FDPs) manufactured from zirconia frameworks and veneered with a press ceramic. Material and Methods. Two mandibular premolars were prepared either with a box inlay cavity or with a full crown chamfer preparation and then duplicated. 40-three-unit cantilever FDPs replacing one premolar, with a group size of eight for each design, were manufactured. In group i-i the cantilever FDPs were retained by two inlays, in group i-c by an inlay–crown combination, and in group c-c by two crowns. The frameworks in groups i-c-R and c-c-R were reinforced by an additional shoulder on the oral side of the zirconia frameworks. All FDPs were subjected to thermal cycling (TC) and 600,000 cycles of mechanical loading (ML) with 50 N. The load to fracture was measured and fracture sites were evaluated. Results. The mean fracture values ranged from 172 N to 792 N. Fracture-strength values were significantly lower for the i-i retained FDPs than for the i-c and c-c combinations. There was no significant effect of the reinforcing shoulder in groups i-c-R and c-c-R. For FDPs with a crown on the terminal tooth, fractures were usually within the distal wall of the distal crown. Conclusions. Inlay–inlay retained cantilever FDPs cannot withstand the mastication forces expected. Fracture load values for inlay–crown and crown–crown-retained FDPs encourage further clinical investigation. The mode of fracture indicates that reinforcement of the distal crown wall might enhance fracture resistance.

Microstructure and material properties of double-network type fibrous (Al 2O 3–m-ZrO 2)/t-ZrO 2 composites

Al 2O 3–(m-ZrO 2)/t-ZrO 2 composites with a novel double-network microstructure were fabricated by multi-pass extrusion process using polymer bound ceramic green body. A simultaneous micro- and macro-level microstructure tailoring was made where unidirectionally aligned two-phase Al 2O 3–(m-ZrO 2) fibers were enclosed in a t-ZrO 2 phase connected in a network formation and this network was further enclosed in a thicker t-ZrO 2 phase. Composite green rods were hot extruded and reassembled in parallel for extrusion and after several passes of extrusion very fine microstructure with dimension of a few micrometers was obtained. Material properties such as hardness, bending strength and fracture toughness were measured for the composites. Microstructure characterization was carried out by SEM technique. In the 4th passed Al 2O 3–(m-ZrO 2)/t-ZrO 2 composites, the outer network of t-ZrO 2 was 15 μm, inner network 0.8 μm and the inner Al 2O 3–(m-ZrO 2) core was 2.5 μm. The highest hardness, fracture strength and toughness values were about 1452 Hv, 1006 MPa and 8.6 MPa m 1/2, respectively, in the sample sintered at 1500 °C.

Investigations of subcritical crack propagation of the Empress 2 all-ceramic system

Introduction The mechanical properties and slow crack propapagation of the all-porcelain system Empress ® 2 (Ivoclar Vivadent, Schaan, Liechtenstein) with its framework compound Empress ® 2 and the veneering compounds “Empress ® 2 and Eris ® were examined. Methods For all materials, the fracture strength, Weibull parameter and elastic moduli were experimentally determined in a four-point-bending test. For the components of the Empress ® 2 system, the fracture toughness K IC was determined, and the crack propagation parameters n and A were determined in a dynamic fatigue method. Using these data, life data analysis was performed and lifetime diagrams were produced. The development of strength under static fatigue conditions was calculated for a period of 5 years. Results The newly developed veneering ceramic Eris ® showed a higher fracture strength ( σ 0 = 66.1 MPa) at a failure probability of P F = 63.2%, and crack growth parameters ( n = 12.9) compared to the veneering ceramic Empress ® 2 ( σ 0 = 60.3 MPa). For Empress ® 2 veneer the crack propagation parameter n could only be estimated ( n = 9.5). This is reflected in the prognosis of long-term resistance presented in the SPT diagrams. For all materials investigated, the Weibull parameter m values (Empress ® 2 framework m = 4.6; Empress ® 2 veneer m = 7.9; Eris ® m = 6.9) were much lower than the minimum demanded by the literature ( m = 15). Significance The initial fracture strength value alone is not sufficient to characterize the mechanical resistance of ceramic materials, since their stressability is time-dependent. Knowledge about the crack propagation parameters n and A are of great importance when preclinically predicting the clinical suitability of dental ceramic materials. The use of SPT diagrams for lifetime calculation of ceramic materials is a valuable method for comparing different ceramics.

Fracture strength of teeth with flared root canals restored with glass fibre posts

To investigate the fracture strength and pattern of failure of teeth with weakened roots reconstructed by different procedures. In an in vitro study root posts were placed in 50 endodontically treated canines, divided into 5 groups (n=10) as follows: cast metallic post; glass fibre post with smaller diameter than the root canal; glass fibre post with smaller diameter than the root canal + glass fibre strips; glass fibre post with smaller diameter than the root canal + accessory glass fibre posts; anatomical post (glass fibre post with smaller diameter than the root canal, relined with low viscosity composite resin). Posts were luted with resin cement and the coronal portion of posts was constructed with composite resin. Metallic crowns were cemented on the posts. Specimens were submitted to compressive load in a universal testing machine. Fracture strength values of each group were compared. Fracture strength values were for Groups 1-5 respectively: 1087.06; 745.69; 775.41; 920.64; 876.12kgf, with significant differences between Groups 1 and 2 and between Groups 1 and 3 (p<0.05). Observed patterns of fracture were: Group 1 - 100% of roots fractured; Groups 2 and 4 - variable fracture modes; Group 3 - 60% of fractures occurred in the cervical root third; Group 5 - 50% of failures occurred in the coronal portion of the post. The fracture strength of teeth with cast metallic posts, teeth with anatomical posts or teeth with glass fibre posts combined with accessory posts was similar. All teeth restored with cast metallic posts presented fractures and were unfavourable to maintenance of the remaining tooth structure. Teeth with fibre posts (Groups 2 to 5) presented variable fracture modes; however, the maximum percentage of unfavourable fractures was 30%.

Effect of grain width and aspect ratio on mechanical properties of Si3N4 ceramics

Sintering additives Y2O3 and Al2O3 with different ratios ((Y2O3/Al2O3) from 1 to 4) were used to sinter Si3N4 to high density and to induce microstructural changes suitable for raising mechanical properties of the resultant ceramics. The sintered Si3N4 ceramics have bi-modal microstructures with elongated β-Si3N4 grains uniformly distributed in a matrix of equiaxed or slightly elongated grains. Pores were found within the grain boundary phase at the junction regions of Si3N4 grains. The highest average aspect ratio (length/width of the grains) of ∼4.92 was found for Y2O3/Al2O3 ratio of 2.33 with fracture toughness and strength values of ∼7 MPam1/2 and 800 MPa, respectively. The effect of microstructure, specifically grain morphology, on mechanical properties of sintered Si3N4 were investigated and found that the aspect ratio of the elongated grains is the most important microstructural feature which controls mechanical properties of these ceramics.

In Vitro Evaluation of Five Core Materials

This in vitro study determined the fracture strength of five core materials supported by two different endodontic dowels. Diametral tensile strength and microhardness of the three resin composite core materials used in this study were also tested. The fracture strength study used one lanthanide-reinforced flowable resin composite (Ti-Core Auto E), one titanium- and lanthanide-reinforced composite (Ti-Core), one lanthanide-reinforced composite (Ti-Core Natural), and two metal-reinforced glass ionomer core materials (Ketac Silver and GC Miracle Mix). Two types of dowels were used: a multitiered, split-shank threaded dowel with a flange (#1 Flexi-Flange) and one without a flange design (#1 Flexi-Post). The specimens were divided into ten groups. Each tooth/dowel and core specimen was placed in a special jig at 45 degrees and subjected to a load by a universal testing machine. The diametral tensile strength and the microhardness of the three resin composite core materials were measured by a universal testing machine and Barcol hardness tester, respectively. All test groups contained ten specimens. The fracture strength value of the resin composite core materials was significantly larger ( p < 0.0001) than those for the metal-reinforced glass-ionomer core materials. Analysis of variance (ANOVA) also showed that the Flexi-Flange dowel interacted with Ti-Core and Ti-Core Auto E to significantly ( p < 0.0013) increase the fracture strength relative to the Flexi-Post. One-way ANOVA revealed that there were no significant differences between them in terms of diametral tensile strength. The Barcol hardness values of the composite core materials were statistically different ( p < 0.0001), with the Ti-Core the highest, followed by Ti-Core Natural, then Ti-Core Auto E. Resin composite core material performed better than glass ionomer material in this in vitro study. The flowable composite core material performed about the same in terms of fracture strength and diametral tensile strength compared with nonflowable composites. Combined with certain core materials, the flange design increased the fracture strength of the tooth/dowel and core combination.

Fabrication of Binary Ni‐Nb Bulk Metallic Glass with High Strength and Compressive Plasticity

Off‐eutectic Ni61.5Nb38.5 alloy, exhibiting the highest glass‐forming ability in the binary Ni‐Nb system, can be cast into the 1.5mm‐diameter fully amorphous rods by using copper mold injection casting method. Room temperature uniaxial compression tests yield for the high fracture strength and compressive plastic strain values of about 3.4GPa and 2%, respectively. The successful fabrication of the bulk metallic glassy samples in the binary Ni‐Nb alloy is of great interest to prepare large dimension Ni‐based bulk metallic glasses as structural materials.

Design and production of ceramic laminates with high mechanical resistance and reliability

A design and processing approach for high failure resistance and increased damage tolerance in laminated ceramic structures is presented. Layers of different compositions are stacked in order to develop a specific residual stress profile by the sintering process. The fracture toughness of the laminate is related to the residual stress. The fracture toughness behaviour can be tailored so that surface defects are forced to grow in a stable way before becoming critical. In this way a ceramic with a unique value of fracture strength is obtained. Laminates composed of alumina/mullite and alumina/zirconia layers have been designed and fabricated. These materials possess a strength of 700 MPa with a standard deviation of <4%. The strength is insensitive to surface damage and in good agreement with the design value.

Partial coverage restoration systems on molars – comparison of failure load after exposure to a mastication simulator

This in vitro study evaluated the failure load of partial coverage restorations (PCR) made of various materials cemented on natural molars after exposure to the mastication simulator. Sixty-four maxillary molars were divided into four groups of 16 test specimens each. The specimens in one group remained unprepared (group NP); the teeth in the other groups were prepared equally according to standardized guidelines and restored with the following PCR: Group GO (Gold-Pontor-MPF; Metaux Precieux SA, Metalor, Neuchatel, Switzerland), group TA (Targis; Ivoclar Vivadent AG, Schaan, Liechtenstein) and group EM (IPS-Empress; Ivoclar Vivadent AG). The restorations in group GO were cemented conventionally, while those in groups TA and EM were luted adhesively. Groups NP and GO served as control groups. All test specimens were subjected to 1.2 million cycles (F = 49 N) in a mastication simulator. Subsequently, all test specimens were loaded occlusally until fracture occurred using an universal testing machine. All specimens withstood the masticating simulation. The median (IQR = x(0.25)-x(0.75)) failure loads were as follows: group NP: 1960.3(1480.5-2227.5) N, group TA: 1478.6(1293.4-1856.7) N and group EM: 1400.1(1043.1-1721.6) N. All test specimens of group GO achieved fracture strength values which exceeded a fracture load of 5500 N. The values of group GO were statistically significantly higher than those of groups NP, TA and EM (P < 0.00001). Furthermore, the results of group NP were significantly higher (P = 0.0226) than those of group EM. The results of groups NP and TA (P = 0.2022) as well as of groups TA and EM (P = 0.5340) did not differ significantly. The median values of all PCR systems obtained were within the limits of clinical acceptance. Long-term clinical investigations which take additional parameters into consideration are required before the composite-based Targis(R) (Ivoclar Vivadent AG) material can be recommended for indirect PCR.

Effect of cyclic loading on fracture strength of endodontically treated teeth restored with conventional and esthetic posts

Introduction:Esthetic post and core systems were recently introduced. There are few reports regarding their behavior under cyclic loading.Objectives:This study compared the effect of cyclic loading on survival rate, residual strength and mode of fracture of endodontically treated teeth restored with esthetic and direct metallic post systems subjected to mechanical cyclic loading.Materials and Methods:Thirty canines were endodontically treated, decoronated and prepared for metal free ceramic crowns, leaving 1.5 mm of dentin for ferrule effect. They were distributed in 3 groups and restored as follows: group 1 with zirconia posts (Cosmopost) and glass-ceramic cores (IPS Empress Cosmopost); group 2 with fiber reinforced composite posts (FibreKor) and group 3 with titanium posts (AZthec Anchor). Direct resin composite (Build It FR Resin Composite) was used as core in groups 2 and 3. All specimens were restored with all ceramic crowns (IPS Empress 2). A resin cement/adhesive system (Cement It/Bond It Primer A+B) was used to lute the posts to root canals and metal free porcelain crowns to the teeth preparation. Specimens were subjected to mechanical load of 250 N for 500,000x at a frequency of 1.7 Hz and then to static load until failure in a universal testing machine. Data were analyzed using One-way ANOVA and Fischer Exact tests α=0.05.Results:All groups had 100% survival rate after cyclic loading; fracture strength values (SD) in N were: group 1 = 886.5(170.6), group 2 = 762.2(113.6) and group 3 = 768.9(72.9); there was no difference among groups (p=0.08); the percentage of mode of favorable fracture found was: group 1 = 60%, group 2 = 90% and group 3 = 50%; there was no correlation between the mode of failure and post and core system used (P=0.142).Conclusions:Esthetic post and core systems showed statistically equivalent fracture strength values, mode of failure and survival rate compared to conventional direct metallic post and resin composite core system after cyclic loading.

Modulus, Fracture Strength, and Brittle vs. Plastic Response of the Outer Shell of Arc-grown Multi-walled Carbon Nanotubes

The fracture strengths and elastic moduli of arc-grown multi-walled carbon nanotubes (MWCNTs) were measured by tensile loading inside of a scanning electron microscope (SEM). Eighteen tensile tests were performed on 14 MWCNTs with three of them being tested multiple times (3×, 2×, and 2×, respectively). All the MWCNTs fractured in the “sword-in-sheath” mode. The diameters of the MWCNTs were measured in a transmission electron microscope (TEM), and the outer diameter with an assumed 0.34 nm shell thickness was used to convert measured load-displacement data to stress and strain values. An unusual yielding before fracture was observed in two tensile loading experiments. The 18 outer shell fracture strength values ranged from 10 to 66 GPa, and the 18 Young's modulus values, obtained from a linear fit of the stress–strain data, ranged from 620 to 1,200 GPa, with a mean of 940 GPa. The possible influence of stress concentration at the clamps is discussed.

Fracture resistance of different partial-coverage ceramic molar restorations: An in vitro investigation

The authors conducted a study to evaluate the influence of preparation design on reliability and fracture resistance of press-ceramic posterior partial-coverage restorations (PCRs) under fatigue. They compared the results for PCRs fabricated of a new press ceramic (IPS e.max Press-VP 1989/4, Ivoclar-Vivadent, Schaan, Liechtenstein) with results for ceramic inlays and unprepared molars. The authors randomly divided 96 human upper molars into six equal groups. Control group NP specimens remained unprepared. Control group IN specimens received a mesio-occlusal-distal (MOD) inlay preparation. The test groups received PCR preparation designs based on group IN's inlay design, with additional cuspal reduction that increased from group to group. The authors fabricated 16 ceramic inlays and 64 PCRs of IPS e.max Press and luted them adhesively. All specimens underwent masticatory fatigue loading (1.2 million cycles, 1.6 hertz, 98 newtons), 5,300 thermal cycles and observation for fracture patterns. Afterward, the authors loaded all surviving specimens until fracture. No fractures occurred during the exposure to the masticatory simulation. After undergoing loading in a universal testing machine, the groups showed no significant differences in fracture strength values (P = .6026). Thus, the different preparation designs of the PCRs demonstrated no significant influence on the restorations' fracture resistance. The median failure loads ranged from 1,567 to 1,960 newtons. All-ceramic PCRs for molars made of IPS e.max Press were shown to be fracture-resistant, results comparable with those of natural unprepared teeth. When a posterior ceramic PCR is indicated, the clinician should perform a defect-oriented preparation that preserves tooth structure. Further clinical investigations are recommended to verify the authors' in vitro results.

Effect of dentin bonding and ferrule preparation on the fracture strength of crowned teeth restored with dowels and amalgam cores

It is necessary to obtain an adequate bond at the core/dentin junction where the majority of failures occur. The effect of recently developed dentin bonding agents on the fracture resistance of endodontically treated teeth at the amalgam core/dentin junction is unclear. The purpose of this study was to evaluate the effects of 2 dentin bonding agents and a ferrule preparation on the fracture resistance of crowned mandibular premolars incorporating prefabricated dowel and silver amalgam cores. Sixty extracted mandibular second premolars were divided into 6 groups of 10 each. The coronal portion of each tooth was removed at the cemento-enamel junction (CEJ) in the first 3 groups. In the other groups, teeth were sectioned 1 mm above the CEJ to create a ferrule. After root canal preparations, prefabricated dowels (ParaPost) were placed. The first group served as a control and was tested without application of bonding agents and without incorporation of a ferrule design. In the second and third groups, respectively, an autopolymerizing adhesive (Superbond D-Liner) and a dual-polymerizing adhesive (Panavia F) were applied to tooth surfaces before restorative procedures. For the fourth (ferrule) group, no bonding agent was applied, but a 1-mm ferrule preparation was used. In the fifth (ferrule+D-Liner) and sixth (ferrule+Panavia F) groups, respectively, autopolymerizing and dual-polymerizing bonding agents were used in conjunction with the ferrule preparation. After amalgam core fabrication, Ni-Cr full cast crowns for each group were prepared and cemented. All specimens were stored in water for 1 week and thermal cycled 1000 times between 5 degrees and 55 degrees C. A compressive shear load was applied at an angle of 135 degrees to the crown, and the maximum load at fracture (N) was recorded. The data were analyzed with 1-way ANOVA and Tukey Honestly Significant Difference tests (alpha=.05). Significantly higher fracture strength values were demonstrated for the ferrule+Panavia F (652.5 N), ferrule+D-liner (649.1 N) and ferrule (592.4 N) groups, respectively, than for the other groups. The next highest fracture strength values were found for the D-Liner (485.0 N) and Panavia F (486.3 N) groups. The control group (376.6 N) demonstrated the lowest fracture strength in all test groups (P<.001). A ferrule preparation or a bonding agent designed for silver amalgam core-dentin bonding can each increase the fracture strength for teeth receiving cast crowns after endodontic therapy and dowel and amalgam core restorations.

Electrical and mechanical properties of superconductingMgB2/Mg metal matrix composites

MgB2/Mg composites were prepared using a metal matrix composite fabricationmethod that offers the potential to produce superconducting wires as analternative approach to the powder in tube process. To obtain composites,MgB2 and Mg powders were mixed at different weight fractions and uniaxially pressed in acylindrical die under the pressure of 0.5 and 1.0 GPa for two hours at varioustemperatures. The x-ray diffraction technique was used for phase identification.Temperature dependence of resistivity and magnetization measurements werecarried out to determine superconducting properties. The effects of compositefabrication temperature and the addition of the Mg on the mechanical properties ofMgB2/Mg composites were investigated. For this purpose, the compressive mechanical testing wasperformed to measure the elastic modulus and fracture strength values of the composites. Itwas found that the relative weight fraction of the Mg and the fabrication conditions of thecomposites have considerable effect on the superconducting and mechanical properties ofthe composites.

Processing of bulk metallic glasses with high strength and large compressive plasticity in Cu50Zr50

Fully metallic glassy rods of 1.5 mm diameter were successfully prepared in binary Cu50Zr50 alloy by copper mould injection casting method. The samples were characterized by X-ray diffraction, differential scanning calorimetry and high-resolution transmission electron microscopy (HRTEM). Room temperature uniaxial compression tests for the Young’s modulus, fracture strength and total strain yield values of about 88 GPa, 2550 MPa and 11.7%, respectively. Significant work hardening is also observed from the stress–strain curves. The 1–2 nm scale medium-range ordering revealed by HRTEM investigations is thought to be responsible for the high strength, significant work hardening and large plasticity of the samples.