Physico-mechanical properties of the wood of freijó, Cordia goeldiana (Boraginacea), produced in a multi-stratified agroforestry system in the southwestern Amazon

ABSTRACT Agroforestry systems (AFSs) integrate, through sustainable practices, agricultural and forest crops for the production of wood and food, providing environmental services, and conserving biodiversity. The freijó (Cordia goeldiana) has potential for cultivation in the Amazon for timber purposes, but data on the characteristics of its wood produced in AFSs are scarce. Our objective was to determine the physical-mechanical properties and suggest technological applications of freijó wood produced in a multi-stratified AFS established in the state of Rondônia, Brazil in 1996. Agricultural and forest species were established in the AFS in double rows with 5.0-m x 2.5-m spacing. Three 19-year-old freijó trees were harvested for chemical, physical (density and dimensional stability), and mechanical (compression, static bending, Janka hardness, and shear strength) characterization of the wood. The wood presented a chemical composition similar to tropical hardwoods, was moderately heavy (582.63 kg m-3), and had high dimensional stability in comparison with other consecrated woods on the market (longitudinal, radial, and tangential retraction = 0.25, 4.27, and 6.83%, respectively). The values determined for parallel (32.32 MPa) and perpendicular compression (8.02 MPa), specific strength (55.32 MPa kg-1 m-3), parallel (2373.33 N) and perpendicular Janka hardness (2326.67 N), strength to static bending (63.5 MPa), and shear (5.94 MPa) were similar to the values observed in other high-density tropical woods grown in either monoculture plantations or natural forests. The wood under study is suitable for manufacture of high-value-added products, such as fine furniture, residential floors, musical instruments and structural pieces.

Push-Out Bond Strength, Characterization, and Ion Release of Premixed and Powder-Liquid Bioceramic Sealers with or without Gutta-Percha

Objective. To evaluate the push-out bond strength of premixed and powder-liquid bioceramic sealers with or without gutta-percha (GP) cone. Materials and Methods. Radicular dentin samples were prepared from 80 single-rooted human teeth. After root canal preparation using ProTaper® and irrigation with NaOCl and EDTA, teeth were divided according to the root canal sealer ( n = 20 ): AH Plus®, EndoSequence® BC Sealer™, ProRoot® Endo Sealer, and BioRoot™ RCS. Samples were randomly divided into two subgroups ( n = 10 ): GP-S: root canal filling using the single-cone technique, or S: filling with only sealer. Specimens were kept at 37°C and 100% humidity in calcium-free PBS for 30 days. The push-out bond strength was measured in MPa. Fractured specimens were observed at 25x to evaluate the type of failure. pH and calcium ion release were measured at different experimental periods. Raman and SEM-EDAX analyses were performed for root canal sealers. Data were analysed using three-way analysis of variance (ANOVA) and post hoc Tukey test at a significance of P < 0.05 . Results. Push-out bond strength was greater for samples obturated with only sealers (S) than samples obturated with the single-cone technique (GP-S) ( P < 0.05 ). BioRoot™ RCS had greater bond strength than EndoSequence® BC Sealer™. Adhesive failures between cement and gutta-percha cone (87.5%) were predominant in the GP-S. Cohesive failures were predominant for S (80%). BioRoot™ RCS and ProRoot® ES presented higher alkalinization potential than the premixed sealer (EndoSequence® BC Sealer™). Powder-liquid bioceramic sealers (BioRoot™ RCS and ProRoot® ES) released the highest cumulative amount of calcium (28.46 mg/L and 20.05 mg/L). Conclusion. Push-out test without gutta-percha cone presents higher bond strength for bioceramic sealers. Powder-liquid calcium silicate-based sealers present greater bioactivity related to alkalinization potential and calcium ion release.

Comparison of Silicon Die Strength Using Different Loading Anvil Shapes

Die fracture strength measurement is important to assess the robustness of a specific silicon die such that it is strong enough to resist die crack. There are several methods used to measure the strength of silicon die and 3-point bend test is the most common. However, the impact of the loading anvil shape on die strength results needs to be investigated. This paper discusses the comparison of die strength characterization using different loading anvil shapes in a 3-point bend test. The anvil shapes considered were wedge shape and needle shape. Die strength calculations were all done using the standard 3-point bend formula for flexural stress. Statistical analysis of the results revealed that die strength measured using wedge shape loading anvil is not significantly different from the strength measured using the needle shape loading anvil. Therefore, using the needle shape loading anvil in a 3-point bend test could still provide die strength results comparable with the results using the standard wedge shape loading anvil.

Pressure Assisted Development and Characterization of Al-Fe Interface for bi-metallic Composite Castings: An Experimental and Statistical Investigation for Low Pressure Regime

Review of the available literature indicates that development of metal reinforced castings present intriguing prospects but carry inherent challenges owing to differences in thermal coefficients, chemical affinities, diffusion issues and varying nature of intermetallic compounds. It is supported that pressure application during solidification may favorably influence the dynamics of the aforementioned issues, nevertheless, not only certain limitations have been cited but also some pressure and process regimes have not been found to be investigated and optimized. This work employs the pressure-assisted approach for bi-metallic steel reinforced aluminum composite castings at low-pressure regime and thoroughly investigates the role of three process parameters namely pouring temperature (800°C-900°C), pressure (10–20 bars) and holding time (10–20 sec) for producing sound interfaces. Taguchi L9 orthogonal array has been employed as DOE while dominant factors have been determined via ANOVA and Grey relational analysis multi-objective optimization technique. Supplementary analysis through optical micrographs, SEM and EDS has been relied upon to quantify interfacial layer thicknesses and to study microstructural and compositional aspects of the interface. Nano-indentation tests under static and dynamic loading have also been performed for mechanical strength characterization. It has been found that uniform interfaces with verifiable diffusion are obtainable with pouring temperature being the most influential parameter (PCR 92.84%) in this pressure regime. Optimum parameters determined from the work, yield ~ 328% thicker interface layer, 19.42% better nano-hardness and 19.10% improved cooling rate when compared to the process conditions with least parametric levels.

Mechanical strength characterization and modeling of hydroxyapatite/tricalcium phosphate biocomposite using the diametral-compression test

This study reports the enhanced mechanical resistance of the composite bioceramics of hydroxyapatite (HAP) and tricalcium phosphate (β-TCP) used as bone substitute. HAP/β-TCP mixture was prepared by wet mixing of powders and characterized. Effects of powder manufacturing and sintering temperature on the densification, microstructure and mechanical properties of the composite were studied. The rupture strength (σr) was calculated using the Brazilian test. At 1250 °C, the relative density and mechanical strength of the HAP/β-TCP ceramics reached the maximum value of 89% and 43 MPa, respectively. Experimental results were modeled by the finite element method to determine the stress distribution in the compacted disc.

Fracture Strength Characterization of the Die Active Side and Back Side for a Realistic Die Crack Assessment

This paper discusses the characterization of an integrated circuit (IC) silicon die fracture strength to have a realistic die crack assessment. The evaluation was conducted using a 3-point bend test setup to measure the die strength of actual IC dies. Both the active side and the back side of the IC die were tested for 2 types of dies with different active side circuit layout. Results showed that the difference in the die active side circuit layout or structure has impact on die strength. It was also found that the active side was weaker than the back side. This implies that both the active side and the back side of an actual IC die must be subjected to fracture strength characterization to have an assessment that would be in a better agreement with real condition. Using only the strength of the back side would result in over-estimating the die strength. The common approach of using the fracture strength of the die back side to characterize the die strength is not realistic and can mislead the assessment of die crack or semiconductor package robustness.