Strength Values Range Research Articles

Variations in Size of Sugarcane Bagasse Fiber as Raw Material for Making Environmentally Friendly Plates

Plastic is a material that is often used as a storage medium, equipment and also furniture to support human activities, but plastic is not easily broken down by the environment. Bioplastic technology is one of the efforts made to address the problem of plastic packaging which can pollute the environment. Environmentally friendly plates, bioplastic products made from tapioca, glycerol and sugar cane bagasse. This research aims to determine the effect of variations in the size of bagasse on tensile strength, elongation at break, water resistance and biodegradability of environmentally friendly plates and to obtain the best formulation of varying sizes of bagasse as raw material for making environmentally friendly plates. This research used a Completely Randomized Design (CRD) with one factor, namely variation in the size of the bagasse. The results of this research show that there is a real influence between tensile strength, water resistance and biodegradability, however, in the elongation test, variations in bagasse did not have a significant effect. Tensile strength values range from 20.00 N/mm2 to 47.72 N/mm2. The largest elongation value is 4.08%. The highest water resistance is at room temperature, namely 88.86% with a degree of curvature of 16⁰ and in water with a temperature of 60⁰C, namely 85.02% with a degree of curvature of 18.75⁰. Variations in the size of bagasse also affect the biodegradability of environmentally friendly plates which ranges from 11.77% to 14.65%. The best treatment is a sample with a variety of bagasse sizes of 60 mesh, because it has high strength compared to other samples.

Weathering and River Erosion: Insights from the Variation of Intact Rock Strength in Rhyodacites

The relationship between weathering and fluvial erosion is important in shaping the incisions of bedrock channels. In rhyodacites from Paraná Volcanic Province, plucking and macro-abrasion processes are predominant in the fluvial incision process, according to field observations. Using the intact rock strength as a proxy for the weathering, this paper analyzes how the strength of rhyodacites behave along a cross section of a bedrock channel and seeks to understand how this affects erosion. Topography and intact rock strength were surveyed continuously along a 30 m cross section using a Schmidt hammer, model N. Mean, median, and standard deviation were calculated for each meter of the section. The topographic amplitude of the bed in the section is 30 cm, featuring an almost flat geometry. The average strength values range from 30 to 59 R (7.65 to 58.15 MPa). Despite the small topographical amplitude, the general behavior of the rock strength follows the macrotopography of the bed, increasing in the high zones and decreasing in the low zones. The standard deviation, interpreted as directly proportional to the degree of weathering, follows the microtopography of the bed (amplitude ≈ 10 cm), being greater in low areas and smaller in high areas. This association between standard deviation of strength and microtopography reveals the seasonal variation of the water level in the channel, whereby higher moisture in low-lying areas intensifies the weathering of the rock. Weathering affects the density of rhyodacites in the area with a minimum reduction of 11.2% being calculated. This enhances the erosion processes by plucking and macroabrasion by reducing the intact rock strength. The susceptibility of the rhyodacites to weathering, despite the differences within the section, favors the maintenance of the rectangular geometry of the channel and shows how erosive processes are affected by the condition of the rock. The study revealed that the notion of decreasing the intact rock strength towards the banks associated with greater weathering in higher areas, cannot be generalized, as it depends on the geometry of the channel section, the lithological nature of the bed, and the frequency of flows.

A synthetic strategy towards sulfonated all-aromatic polyamides and poly(benzoxazole-co-amides)

Herein, we describe the synthesis and properties of a liquid crystal all-aromatic polyamide with tunable sulfonated content that can be converted into its poly(benzoxazole-co-amide) analog using a simple thermal treatment step. The parent all-aromatic polyamide, poly(3,3′-dihydroxybenzidine terephthalamide) (DHTA), is modified by incorporating a sulfonated comonomer, 2,5-diaminobenzenesulfonic acid (DABS) (i.e., 5, 10, 25, and 50 mol% DABS), to yield sulfonated, random copolyamides (DHTA-y-DABS). The ortho-positioning of the hydroxyl group relative to the amide bond allows DHTA-y-DABS to undergo a cyclodehydration reaction from 200 to 450 °C, forming a sulfonated poly(benzoxazole-co-amide) while preserving the sulfonate functionalities. Swelling experiments show that the DHTA-y-DABS-Na+ films exhibit water uptake values ranging from 9 to 41 wt%. PBO-y-DABS-Na+ films swell between 4 and 15 wt% in water. Dry films exhibit excellent mechanical properties. Young's moduli are between 8 and 10 GPa, yield strength values range from 117 to 215 MPa and elongation at break values range from 3 to 10%.

Influence of Heat Input on the Weldability of ASTM A131 DH36 Fillet Joints Welded by SMAW Underwater Wet Welding

Naval vessels face multiple risks that can damage their hulls during navigation, leading to on-site repairs through the shield metal arc welding (SMAW) process and underwater wet welding (UWW). This paper presents a weldability study to identify the optimal heat input parameters to improve ASTM A131 DH36 welded joints quality, development, and sustainability. This study analyzes the influence of heat input on the microstructure and mechanical properties of underwater wet welding fillet joints welded with shield metal arc welding at 4 m water depth in a real-life environment located at the bay of Cartagena (Colombia). The methodology involves nondestructive and destructive tests, including visual inspection, fillet weld break, scanning electron microscopy (SEM), X-ray diffraction (XRD), Vickers hardness, and shear strength tests. The welds microstructure is composed of ferrite, pearlite, retained austenite, bainite, and martensite; the hardness values range from 170 HV1 to 443 HV1, and the shear strength values range from 339 MPa to 504 MPa. This indicates that high thermal inputs improve the weld quality produced by the underwater wet welding technique and can comply with the technical acceptance criteria of AWS D3.6, making them more sustainable, with less welding resources wastage and less impact on marine ecosystems.

Mechanical and acoustic absorption properties of lightweight fly ash/slag-based geopolymer concrete with various aggregates

Acoustic absorption and thermal insulation play a key role in modern buildings to make living comfortable and energy-saving. This paper aims to study the workability, physical and mechanical properties, thermal conductivity, and acoustic absorption of modified geopolymer concrete (GPC) with various types of lightweight aggregates (LWA) such as extruded polystyrene foam beads waste (EPS), vermiculite, or lightweight expanded clay aggregate (LECA). The mixtures of geopolymer concrete have been modified by substituting for the ordinary aggregates (dolomite) by volume with various ratios of 0, 25, 50, 75, and 100% for each type of LWA. Besides, the mechanisms of specimens were examined by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and mapping. The results illustrated that the compressive strength values range between 8.5 and 47.50 MPa. The hardened density of concrete was between 1500 and 2450 kg/m3, and thermal conductivity was between 0.45 and 1.16 W/m.K. Geopolymer concrete was considered an acoustic absorption and thermally insulating material. Geopolymer concrete was considered an acoustic absorption and thermally insulating material. EPS, vermiculite, and LECA will be beneficial for applications in lightweight geopolymer concrete due to their capability to reduce weight and excellent thermal conductivity, and the property of improving acoustic absorption. The mechanical results indicated that 25% LECA was the best compared with the ratios of other LWA and gained 35.0, 2.7, and 4.3 MPa of compressive, splitting tensile and flexural strength, respectively. It had positive workability; the thermal conductivity was 1.1 W/m.K, and hardened density was decreased to 10% compared to the control. In addition, LECA is considered the superior and suitable material for acoustic absorption compared with other aggregates.

Influence of Stress Relief Annealing Parameters on Mechanical Properties and Decomposition of Eutectic Si Network of L-PBF Additive Manufactured Alloy AlSi10Mg

This paper evaluates the effect of stress-relieving heat treatment on the AlSi10Mg alloy prepared by additive manufacturing using the Laser Powder Bed Fusion (L-PBF) with print parameters: 370 W, 1400 m/s, and 50 μm. The as-built state and four different annealing modes (240 °C/2 h, 240 °C/6 h, 300 °C/2 h, and 300 °C/2 h/water-quenched) are investigated. To determine the effect of the annealing mode on the mechanical properties of the L-PBF AlSi10Mg alloy, heat-treated samples were compared with the as-built state and with each other. The mechanical properties of the samples were determined by tensile and hardness tests. The strength in the as-built state is 488 MPa, depending on the method of heat treatment, the strength values range from 296 MPa to 417 MPa, and the HV10 hardness values are in accordance with the measured strength values. Furthermore, the microstructure of the samples was investigated by scanning electron microscopy (SEM) analysis, which was then linked to the measured mechanical properties. The composition of the microstructure of the alloy and its influence on the mechanical properties were determined by energy dispersive spectroscopy (EDS) analysis. Furthermore, the differences between the individual heat treatments in comparison with the as-built state were analyzed and the phenomenon of decomposition of the silicon network after reaching specific temperatures was discussed and confirmed. The paper evaluates the effect of dwelling time on stress relief annealing. It was found that if annealing at intermediate temperatures of 240 and 300 °C is applied, changes in structure and mechanical properties are more temperature- than dwell-time-dependent.

Mechanical Properties of Pervious Concrete Containing East Borneo Local Aggregate

This article identifies the potential of East Borneo local aggregates as a material in producing pervious concrete. East Borneo has to import material from another island (Palu / Central Sulawesi), which ends up with a high price in the concrete unit. In addition, high population growth, continual urbanization, rapid infrastructure development have reduced the infiltration area. This problem increases surface runoff, which can involve flooding. Research on the potential of local aggregates for porous concrete materials needs to be carried to reduce this problem. In this study, several coarse aggregates in East Borneo were used: Senoni, Cermin, Suryanata, and Muara Asa aggregates. This material is compared with Palu aggregate, which currently use in East Borneo. The tests such as compressive strength, split tensile strength, and flexural strength were carried out. Results of this research show that the concrete performance varies widely amongst the different aggregates. The compressive strength, flexural strength, and split tensile strength values range from 9.06 MPa to 21.97 MPa, 1.99 MPa to 3.98 MPa, and 1.38 MPa to 2.95 MPa respectively. Overall, Senoni aggregate is found as the best quality compared to other local aggregates. This research provides an overview of East Borneo local materials as infrastructure development to reduce dependence on Palu materials.

Microstructure, mechanical properties and fracture behavior of NiCoCrTiAl and FeNiCoCr new alternative binders for WC based hardmetals

Hardness and fracture strength of WC-Ni-Co-Cr-Ti-Al cemented carbides have been measured at room temperature in as-HIPed and solution-aged conditions. These treatments are applied to modify the size of gamma prime precipitates, which are intrinsically formed within the metallic binder of these ceramic-metal composites during the sintering process. Compositions containing approx. 28–29 vol% metal content exhibit hardness values in the range of those reported for similar grades of WC-Co hardmetals. Optimized aluminum additions lead to materials with fracture strength values only 15% lower than those reported for the same WC-Co commercial references. These results suggest gamma prime precipitation hardening as a potential strategy for improving the performance of WC-Co materials at high temperatures.Regarding Fe-Ni-Co-Cr alloys are potential candidates for partial substitution of Co content in WC-based hardmetals. It has been investigated WC coarse grade with 15 wt%(FeNiCoCr). The Cr content has been adjusted in order to avoid the precipitation of M7C3 carbides. Within the corresponding carbon windows, fracture strength values range from 2.8 GPa to 3.0 GPa. These values are within the range of standard WC-Co grades with similar binder contents and WC grain sizes.

Environmental friendly packaging based on rice liquid as edible film: a feasibility study

Rice liquid is the water obtained from the process of washing rice. This waste is easy to get because Indonesian people tend to eat rice as their main staple food which results in a lot of rice liquid. The rice liquid waste can be used as the main ingredient of an edible film. This study aims to determine the effect of the addition of sorbitol concentration on the characteristics of the edible film from rice liquid waste which includes thickness, tensile strength, elongation and water vapor transmission rate. The method used in this study is one-way ANOVA completely randomized design (CRD) with 3 variations of sorbitol concentrations, they are: 2%, 4%, and 6% and was carried out three times. The data obtained from the research were then analyzed at a significant level of P<0.05. The parameters tested include thickness, tensile strength, elongation and water vapor transmission rate. The research data shows that the thickness values obtained are between 0.01367 mm - 0.2453 mm, tensile strength values range from 180.61 kgf.cm−2 -159.28 kgf.cm−2, elongation between 190.613% - 186.920%, and water vapor transmission rates between 1.3004 g.m−2.h−1- 4.6444 g.m−2.h−1. The addition of sorbitol variation does not have significant effect (P>0.05) on the tensile strength, elongation and water vapor transmission rate, but had a significant effect (P<0.05) on the thickness of the edible film. A good variation of sorbitol by producing a good edible film made from rice liquid waste is a variation of sorbitol with a sorbitol concentration of 2%.

CHANGES IN THE COMPOSITION AND PROPERTIES OF THE HOST ROCKS OF COAL DEPOSITS IN YAKUTIA UNDER THE INFLUENCE OF CRYOGENESIS

The results of laboratory tests carried out on rock samples of the Kharbalakhskoye coalfield located in Central Yakutia revealed significant secondary changes having taken place in the host rocks containing the coal. Evidently, under transformation processes, it is not only the composition of the rocks that had changed, but also the nature of structural bonds that have a great influence on their physical and mechanical properties. Thus, the ultimate strength values of coal-containing sandstone and siltstone samples under uniaxial compression vary from 20 to 30 MPa, while under uniaxial tension, the ultimate strength values range from 6 to 10 MPa. These relatively low numerical values pertaining to the physicomechanical properties of rocks, which are generally atypical for long-flame coal deposits, are almost 50% lower than those of analogous rocks hosting other coal deposits in Russia. It is considered that the mechanical strength properties of the rocks of the Kharbalakhskoye field are due to significant cryogenic processes. A comparative analysis of the properties of core samples obtained from boreholes drilled in 2019 with samples from a quarry obtained several decades ago reveals signs of transformation of rocks in the Kharbalakhskoye field due to phase transitions of freezing and thawing water.

Geochemical, Index, and Strength Appraisals of Granite-derived Residual Soils

This research work examined the geochemical, index, and strength properties of lateritic residual soils from granitic parent rock in Akure, southwestern Nigeria. The aim is to underscore the potential use of such soils as engineering fills materials. The geochemical method involved the use of X-Ray Fluorescence (XRF). The major oxides determined from this analysis were used for the geochemical quantifications of the soils. Analysis of soil index properties involved consistency limits, grain size distribution and specific gravity tests, while the strength analysis involved compaction and unconfined compressive strength (UCS) tests. Results obtained from the index analysis classified the soil profile into behavioral groups VII and VI. These indicates that the soils are of high to intermediate plasticity and compressibility. The UCS values vary from 272.6 to 377.2 kPa while the shear strength values range from 138.8 to 188.6kPa, indicating good bearing capacity. The geochemical results revealed iron-oxide variations as the major influential constituent within the soil profile. Furthermore, the more lateriterizad zones correspond with the more competent horizons. The residual soils from the study area are found to be suitable materials in engineering construction works as Sanitary landfills and Subgrade materials.

Combined effect of mineral admixtures and fine aggregate on the mechanical properties of ultrahigh performance concrete

The aim of this study was to determine combined effect of mineral admixtures namely fly ash, silica fume as an alternative for cement, and fine aggregate including natural whiter sand (NWS) and finely ground quartz sand as partial replacement of natural river sand (NRS) on the mechanical properties of ultrahigh performance concrete (UHPC) containing steel fiber. Concrete was produced by replacing NRS with 22% upto 100% of NWS consists of particle sizes of 5 to 1800 µm, simultaneously combined with binding materials like fly ash (20, 30 and 40%) and silica fume (5 to 15%) as a substitute for cement in mixtures containing Dramix® 3D steel fiber 65/35 at 100kg/m3, and water curing temperature variation ranging follow ambient temperature from 28-34°C. The results indicated that the NRS was replaced with 100% NWS of 5…1800 µm fraction by weight of NRS, in UHPC containing 20% of fly ash combined with silica fume at the replacement levels of 5 to 15% contributed to improved mechanical properties. Detailed, compressive strength of UHPC obtained values 122, 128, 117, 115.3, and 118.5 MPa respectively. Similar results were also observed for the splitting tensile strength attained at 11.6, 11.9, 11.5, 10.5, 10.2 MPa, respectively, while flexural strength values range between 18.8 to 25.4 MPa. These values higher than compared to that of the NRS reference specimens without containing NWS at 28 days of curing. The achieved experimental results demonstrated that the addition of locally available NWS can be a good substitute for NRS, and therefore, can be effectively used in construction activities, which in turn reduces the depletion on the NRS resources. Furthermore, utilization of by-product materials reduces the carbon footprint of cementitious composites production as well as environmental pollution concerns.

Critical discussion of perpendicular to grain tension testing of structural timber – case study on the European hardwoods ash, beech and maple

ABSTRACT Knowledge about perpendicular to grain tension behavior of wood is essential, since in construction tension stresses perpendicular to grain cannot be avoided completely. Especially for hardwoods, the data basis is scarce. EN 338 design values are with 0.6 N/mm² characteristic strength set very low. The US-American National Design Specifications even set this value to zero and make local reinforcements mandatory. This paper compares strength and stiffness values attained with newly-designed, little, prismatic specimens and EN 408 structural timber specimens to evaluate the current European design values. Little specimen’s characteristic strength values range from 7.2 to 10.6 N/mm² and are assumed to be real material properties. EN 408 specimen values are with approximately 4.0 N/mm² lower. These lower values are mainly due to stress peaks introduced by the force introduction. Strength values attained for the medium-dense European hardwoods beech, ash and maple exceed EN 338 design values by a factor of six to seven. Adaptation of the EN 338 design value is not recommended, though. The abundance of influencing factors makes clear that the design value and the ensuing design code have to be synchronized carefully by tedious testing in order to make use of the perpendicular to grain tension strength potential of the selected hardwoods.

Investigations into Ti-15Mo-W Alloys Developed for Medical Applications.

The β-Ti alloys have attracted the attention of researchers due to their excellent properties and their remarkable biocompatibility. The present study evaluated the mechanical behavior analysis (hardness, compressive strength, and modulus of elasticity) of the Ti-15Mo-W system. For experimental research, we chose the TiMo15 biocompatible alloy as a starting material. In order to improve the mechanical properties, we added tungsten amounts of 3.88 to 12.20 wt.% and analyzed the results obtained. The successive melting of the samples was done using a vacuum arc furnace in a copper crucible cooled with water. Following micro-structural investigations, we found this alloy possessed a homogeneous structure and showed β-phase predominance. The investigated alloys have good mechanical properties—the mean Vickers micro-hardness values are between 251 to 321 HV, the compressive strength values range from 717 to 921 MPa, and the modulus of elasticity is between 17.86 and 45.35 GPa. These results are compatible to the requirements of a metallic material for medical applications as artificial implant devices.

High-strength epoxy nanocomposites for 3D printing

Clay-based nanoscale filler materials are commonly used to impart unique and desirable properties to polymer resins. Small volume fractions of nanoclay have disproportionately large effects on stiffness, toughness, strength, and gas barrier properties of polymer matrices due to their high surface-to-volume ratio and platelet morphology. Recent work has suggested that highly loaded epoxy/clay/fiber mixtures possess desirable rheological properties for use as feedstock materials for direct-write 3D printing, but little is known about the effects of the deposition process on the resulting properties of the printed composites. In this work we characterize the effects of a functionalized nanoclay on the rheological properties and printing behavior of an epoxy resin in the absence of fiber reinforcements, and investigate the effects of clay content and the deposition process on the thermo-mechanical properties of the resulting 3D-printed epoxy/clay nanocomposites. The rheological properties of ink formulations containing up to 12.5 wt% nanoclay are measured using parallel plate rheometry, and the thermo-mechanical properties of the printed composites are measured using 3-pt flexural testing, dynamic mechanical analysis, and thermo-gravimetric analysis. Flexural strength values range from 80 MPa to 100 MPa for cast samples and printed samples tested transverse to the printing direction, and up to 143 MPa for printed samples tested parallel to the print direction. Although the observed anisotropic strength values indicate that the deposition process does impart orientation to the nanoclay, the strength in each direction is significantly greater than values reported for 3D printed thermoplastic composites, suggesting that the epoxy/clay system has high potential for further development as a 3D printing feedstock material.

Engineering Properties of Volcanic Tuff from the Western Part of Yemen

This paper deals with a study of the physical and mechanical characteristics of volcanic tuff and ignimbrite from six quarries located at different areas in the western part of Yemen (Manakha, Jahran, Bakhran, Dar Al-Hanash, Abaser and Soraifa). In the region, volcanic tuffs and ignimbrite are locally known by their location names and have been used as solid masonry and cladding stones. All the investigated pyroclastic rocks belong to the Tertiary volcanic. The standard physical and mechanical tests (void ratio, porosity, density, specific gravity, water absorption, uniaxial compressive strength and tensile strength) were carried out on the tuff and ignimbrite samples collected from different parts of the region. Laboratory tests revealed that the void ratio average values range between 0.12 and 0.37, the porosity ranges between 10.57 and 27.12%, the dry density ranges between 1.66 and 2.25 gm/cm3, specific gravity ranges from 1.45 to 1.94, and water absorption ranges from 4.69 to 16.39%. The measured uniaxial compressive strength values range from 24 to 68 MPa, and the tensile strength values range between 4 and 10 MPa. These tuffs and ignimbrites generally are light green, gray, beige, or yellowish in color. With these colors they are favoured for building, coating and decorative stone. This paper concludes that the studied stones have acceptable to good properties as dimension stone. Jahrani and Manakhi tuffs are the best quality, whereas Hanashi ignimbrite is of poorer quality.

Geological and geomechanical properties of the carbonate rocks at the eastern Black Sea Region (NE Turkey)

Turkey located in the Alpine-Himalayan Mountain Belt has 35% of the natural stone reserves of the world and has good quality marble, limestone, travertine and onyx reserves especially in the western regions of the country. The eastern Black Sea Region with a 1.4 million meters cubes reserve has a little role on the natural stone production in the country. For this reason, this paper deals with investigation on the potential of carbonate stone in the region and determination of the geological and geo-mechanical properties of these rocks in order to provide economic contribution to the national economy. While the study sites are selected among the all carbonate rock sites, the importance as well as the representative of the sites were carefully considered for the region. After representative samples were analyzed for major oxide and trace element compositions to find out petrochemical variations, the experimental program conducted on rock samples for determination of both physical and strength properties of the carbonate rocks. The results of the tests showed that there are significant variations in the geo-mechanical properties of the studied rock groups. The density values vary from 2.48 to 2.70 gr/cm3, water absorption by weight values range from 0.07 to 1.15% and the apparent porosity of the carbonate rocks are between 0.19 and 3.29%. However, the values of the UCS shows variation from 36 to 80 MPa. Tensile and bending strength values range from 3.2 to 7.5 MPa and 6.0–9.2 MPa respectively. Although the onyx samples have the lowest values of apparent porosity and water absorption by weight, these samples do not have the highest values of UCS values owing to occurrence of the micro-cracks. The UCS values of the rock samples were also found after cycling tests However, the limestone samples have less than 5% deterioration after freezing-thawing and wetting-drying tests, but travertine and onyx samples have more than 15% deterioration. Exception of the apparent porosity values of travertine samples, all geo-mechanical properties of the studied carbonate rocks were determined in the acceptance values given by Turkish Standards Institute (TSE) for using as a natural dimension stone. After these investigations, it is anticipated that in the near future the number of quarries and factories will increase and more types of natural stones will be discovered in the eastern Black Sea Region and thus this will provide economic contribution to the economy of the country.

Mechanical and piezoresistive properties of thin silicon films deposited by plasma-enhanced chemical vapor deposition and hot-wire chemical vapor deposition at low substrate temperatures

This paper reports on the mechanical and piezoresistance characterization of hydrogenated amorphous and nanocrystalline silicon thin films deposited by hot-wire chemical vapor deposition (HWCVD) and radio-frequency plasma-enhanced chemical vapor deposition (PECVD) using substrate temperatures between 100 and 250 °C. The microtensile technique is used to determine film properties such as Young’s modulus, fracture strength and Weibull parameters, and linear and quadratic piezoresistance coefficients obtained at large applied stresses. The 95%-confidence interval for the elastic constant of the films characterized, 85.9 ± 0.3 GPa, does not depend significantly on the deposition method or on film structure. In contrast, mean fracture strength values range between 256 ± 8 MPa and 600 ± 32 MPa: nanocrystalline layers are slightly stronger than their amorphous counterparts and a pronounced increase in strength is observed for films deposited using HWCVD when compared to those grown by PECVD. Extracted Weibull moduli are below 10. In terms of piezoresistance, n-doped radio-frequency nanocrystalline silicon films deposited at 250 °C present longitudinal piezoresistive coefficients as large as −(2.57 ± 0.03) × 10−10 Pa−1 with marginally nonlinear response. Such values approach those of crystalline silicon and of polysilicon layers deposited at much higher temperatures.

Quality control of glulam: shear testing of bondlines

In quality control of glulam, shear testing of bondlines is required. However, in relevant standards the method of applying shear stress to the bondline is only exemplified by a principle schematic. Based on this schematic a considerable variety of test equipments is in use nowadays. Depending on the respective construction of the test equipment as well as on the execution of testing, the resulting stress in the bondline is not pure shear but rather a combination of shear and normal stresses. When the normal stresses are acting as tensile stresses perpendicular to the bondline, the registered shear strength values range considerably below the pure shear stress level, whereas compression stresses perpendicular to the grain lead to an overestimation of the shear strength of the bondline. To overcome this deficiency, a prototype of a modified shear test device was developed, which ensures a clearly defined state of shear loading of the specimens. Based on extensive comparative testing it is shown that by performing compression tests at an oblique angle to the grain of 14° the above mentioned problems can be avoided.

In vitro peel/shear bond strength evaluation of orthodontic bracket base design

Objectives: The adhesive capacity of 17 different bracket types was evaluated in an in vitro peel/shear test. Methods: Silane-treated metal bars were used as substrates with all bonding being performed using the orthodontic adhesive Concise. The effect of aluminium oxide air abrasion on the bonding performance of recycled metal bracket bases was evaluated. Morphological examination of the bracket bases was carried out under scanning electron microscopy. Statistics analysis included one-way ANOVA with Tukey's Studentized Range Test, two-way ANOVA and Weibull analysis. Results: Mean peel/shear bond strength values range from 13.9 MPa for Allure Accu Arch, a ceramic bracket type, to 1.6 MPa for the plastic bracket CeramaFlex Advant Edge. Allure Accu Arch performed the best of all the ceramic brackets. However, bracket wing fracture was observed. The metal brackets Mini masters and Omni Arch showed no significant difference in bond strength compared with the ceramic bracket Allure Accu Arch ( P < 0.01). Conclusion: The type of the bracket base determines its adhesive capacity. Sandblasting the base of recycled metal brackets had no uniform effect.