Flexural Strength Of Test Specimens Research Articles

Thermal shock resistance of additively manufactured alumina

AbstractThe mechanical behavior and cracking patterns of thermally‐shocked additively manufactured alumina were investigated. The flexural strength of test specimens that had been heated to temperatures ranging from 200°C to 1000°C and then rapidly quenched in water was determined at ambient temperature by four‐point bending. Results indicated that the surface cracking patterns had a multifractal structure and that an increase in the thermal shock temperature led to an increase in the density and uniformity of the crack network. The flexural strength results were analyzed with Weibull statistics, where the Weibull moduli for most of the thermal shock conditions tested were found to be statistically indistinguishable. It was also found that a significant decrease (∼50%) in flexural strength occurred for heating temperatures ≥300°C. The effect of the manufacturing method on cracking patterns is discussed, as well as the implication of the material behavior for practical applications of these materials.

The Effect of Polymerization Methods and Fiber Types on the Mechanical Behavior of Fiber-Reinforced Resin-Based Composites.

Glass fibers were introduced to increase the fracture resistance ofresin-based composites restorations; however, the poor polymerization between fibers andresin-based compositewere sometimes noted and can cause debonding and failure. The purpose of this study was to investigate the effects of different polymerization methods as well as fiber types on the mechanical behavior of fiber-reinforcedresin-based composites. Seventy-five specimens were fabricated and divided into one control group and four experimental groups (n = 15), according to the type of glass fiber (strip or mesh) and polymerization methods (one- or two-step). A 0.2-mm-thick fiber layer was fabricated with different polymerization methods, on top of which a 1.8 mmresin-based compositelayer was added to make a bar-shape specimen, followed by a final polymerization. Specimens were tested for flexural strength and flexural modulus. The failure modes of specimens were observed by scanning electron microscopy. The fiber types showed significant effect on the flexural strength of test specimens (F = 469.48, p < 0.05), but the polymerization methods had no significant effect (F = 0.05, p = 0.82). The interaction between these two variables was not significant (F = 1.73, p = 0.19). In addition, both fiber type (F = 9.71, p < 0.05) and polymerization method (F = 12.17, p < 0.05) affected the flexural modulus of test specimens; however, the interaction between these two variables was not significant (F = 0.40, p = 0.53). The strip fibers showed better mechanical behavior than mesh fibers and were suggested for resin-based composites restorations reinforcement; however, different polymerization methods did not have a significant effect on the strength and failure mode of fiber-reinforcedresin-based composites.

An Experimental Study of pH Value and Flexural Strength of Cement Sand Mortar with Surface Untreated Multi-Walled CNTs

Background/Objectives: The paper describes the study carried out on test specimens of cement mortar composite admixed with multi-walled carbon nanotubes (CNTs) in order to investigate the physical property changes under nano-level hydration. Methods/Statistical Analysis: In this study, the standard engineering tests such as pH value identification, flexural strength test and compression strength tests were carried out for both control and test specimens which were cast and cured as per Indian Standard specifications. Test specimens of cement mortar composite consisted of ordinary Portland cement and river sand added with 0.2% (by weight of cement) pristine multi-walled CNTs ultrasonicated but without any surface treatment. Findings: The pH value of ultrasonicated multi-walled CNTs dispersed in de-ionised (DI) water was first determined and found to be 6.85. The pH of control mix without multi-walled CNTs was 12.64 and the pH of test mix with multi-walled CNTs was 12.37. The percentage addition of multi-walled CNTs was very small and hence the reduction in alkalinity was found to be equally small. Flexural strength of test specimens showed 23%, 31.41% and 31.46% increase at 7, 28 and 45 days respectively over control specimens. Compressive strength of test specimens showed 6.1% increase at 28 days over control specimens. Application/Improvements: In view of improvement in flexural strength in mortar, addition of multi-walled CNTs to concrete elements may help in improving their performance under dynamic loading. Further improvements are required to study the effect of an increased percentage addition of multi-walled CNTs without any surface treatment and without any surfactant in cement sand mortar (1:3).

Effect of alkali content of cement on properties of high performance cementitious mortar

The use of very low water-to-binder ratio (w/b) in high-performance cementitious mixtures (HPCM) such as ultra-high performance concrete (UHPC) is gaining popularity. Typically these mixtures consist of Portland cement, pozzolans, water, aggregate, chemical admixtures and steel fiber. The properties of such mixtures including workability, strength, dimensional stability and durability are sensitive to the quality and the proportions of the materials used. In particular, due to high cementitious materials content and low w/b ratio of these mixtures, the alkali content of Portland cement can have a significant effect on the fresh and hardened properties. However, there is limited information available in the literature on the influence of cement alkalinity on the properties of these mixtures. In order to have a closer examination of the influence of alkali content of cement on the properties of such mixtures, a series of Portland cement mortars having a w/c ratio of 0.20 and a range of cement alkali contents were evaluated in this study. The workability, setting time, compressive strength, drying shrinkage, rapid chloride ion penetration, volume of permeable voids and alkali–silica reaction potential of HPCM using reactive aggregate were studied as a function of the alkali content of cement ranging from 0.49% to 0.88% Na2Oeq. The test results showed that when the alkali content of cement was higher than 0.70%, the workability of HPCMs decreased significantly as the alkali content increased. An increase in the alkali content of cement delayed the time of final setting, reduced the compressive strength, and increased the rapid chloride ion permeability, drying shrinkage and volume of permeable voids of HPCM. As the alkali content of cement increased, rapid and significant expansion due to ASR was observed in HPCM, along with significant loss in flexural strength of test specimens, even though the w/c was maintained at 0.20. Identical set of tests were conducted on parallel HPCM specimens containing Class F fly ash as a cement replacement material, and significant differences in results were observed when compared with pure Portland cement mixtures.

Acoustic emission analysis of fiber-reinforced composite in flexural testing

Objectives. The aim of this study was to examine the emission of acoustic signals from six commercially available fiber-reinforced composites (FRC) used in the frameworks of fixed partial dentures in material bending. Methods. FRC test specimens were made of six commercially available fiber products of polyethylene or glass and five light-curing resins. FRC test specimens were polymerized with a hand light-curing unit or with a light-curing oven. The flexural test for determination of ultimate flexural strength of test specimens ( n=6) was based on the ISO 10477 standard after the specimens were stored in air or in water for two weeks. The acoustic emission (AE) signals were monitored during three-point loading test of the test specimens using a test with increasing loading levels until the specimens fractured. Results. Generally, stress level required for the AE activity initiation ranged from 107 MPa (Ribbond) to 579 MPa (everStick). The ultimate flexural strength of FRC specimens were higher, ranging from 132 to 764 MPa, being highest with everStick and Vectris FRC, and lowest with Ribbond FRC. ANOVA showed a statistically significant difference between the initiation of AE activity and the ultimate flexural strength according to the brand ( p<0.001), storing conditions ( p<0.001) and polymerization procedure ( p<0.001). AE activity and ultimate flexural strength correlated significantly ( p<0.010, r=0.887). Significance. The result of this study suggested that AE activity in FRC specimens started at a 19–32% lower stress level than occurred at final fracture.

Preliminary investigation of a novel retentive system for hydrofluoric acid etch-resistant dental ceramics

Statement of problem. A potential limitation to clinical use of In-Ceram and In-Ceram Spinell dental ceramics has been the inability to etch fit surfaces. Purpose. This study investigated a novel retentive system for In-Ceram and In-Ceram Spinell ceramics. Material and methods. The system, Bateman etch retention system, relies on incorporation of plastic chips on the surface of a specimen. The plastic chips were subsequently burnt-out to leave pits on the fitting surface of the ceramic restoration. The effect of these surface pits on flexural strength of test specimens was compared with unetched and sandblasted samples. Shear bond strengths between clean and saliva contaminated samples and Panavia TC resinous cement were also determined. Results. The Bateman etch retention system significantly reduced the flexural strength of both In-Ceram and Spinell ceramic specimens compared with unetched and sandblasted samples ( p < 0.05). No significant differences were discovered between shear bond strengths of uncontaminated Bateman etch retention system and sandblasted samples. However, mean shear bond strengths of saliva-contaminated Bateman etch retention system In-Ceram samples were substantially greater than those of saliva contaminated sandblasted samples ( p < 0.05). Conclusion. The Bateman etch retention system method should be the subject of additional investigation. (J Prosthet Dent 1997;78:275-80.)