Reduction In Bending Strength Research Articles

A probabilistic approach to the evaluation of the bending strength of timber beams with integration of data from on-site tests

A probabilistic method to evaluate the bending strength of maritime pine beams (Pinus pinaster Aiton) was explored. The beams were subjected to an experimental campaign that started by allocating them to a visual strength grade and segmenting them lengthwise into clear wood and weak zones. The weak zones are associated with a reduced bending strength that is caused by the presence of knots or grain deviation. Non-and semi-destructive techniques were used to gather information regarding the physical and mechanical properties of the clear wood. Bending tests were carried out until failure to determine the strength of the beams. The method to predict the structural behaviour of the elements was developed under a probabilistic framework based on Monte Carlo simulations in which the reference properties of the beams were assigned randomly based on their probability distributions. The results show that the characteristic strength values assigned to the timber pieces after strength grading only frequently underestimate their strength and that the probabilistic method applied could be used to safely explore the capacity reserve of the timber elements.

Microstructure–mechanical properties correlation in spark plasma sintered Ti–4.8 wt.% TiB2 composites

Abstract Ti TiB2 composites were fabricated from powder mixtures via spark plasma sintering method. Mechanical behavior of the sintered composites were then investigated via both routine and nanoindentation methods. Results indicated a significant increase in ultimate tensile strength and hardness of the composite, when the sintering temperature is raised. Besides common increase in the relative density of the composite, such a behavior was also attributed to the higher amounts of in-situ formed TiB whiskers. The remarkable reduction in bending strength is probably due to limited formability of unreacted coarse TiB2 particles and agglomerated in-situ formed phases. Such findings were then discussed in detail, based on the nanomechanical behavior of the primary and in-situ formed phases in Ti TiB2 composite sintered at 1200 °C. It was concluded that the superiority of mechanical properties in the mentioned sample may be due to high strength primary and in-situ formed reinforcements distributed homogenously in the matrix. Such reinforcement also provided high strength interfaces, according to interfacial nanoindentation approaches.

Physico-mechanical properties of light red meranti (Shorea spp.) and kedondong (Canarium spp.) wood heat treated in convection oven

Physico-mechanical properties of light red meranti and kedondong wood heat treated in a laboratory at 160, 180 and 200 °C for 5, 7 and 9 h were investigated. Weight loss of the treated samples increased along with treatment severity. Heat treatment reduced the hygroscopicity of the wood where reduction in equilibrium moisture content and a positive moisture excluding efficiency was observed. Reduction in bending strength as function of increasing treatment temperature and time were also recorded.

The effect of de- and re-polymerization during heat-treatment on the mechanical behavior of Scots pine sapwood under quasi-static load

Loss in strength and ductility is a major drawback for the heat-treatment of solid wood. Previous studies focused mainly on the de-polymerization of cell wall constituents as a cause and the importance of the preferential removal of hemicelluloses. This study tested the hypothesis that the mechanical behavior of wood is additionally affected by re-polymerization reactions within the cell wall matrix during heat-treatment. This was achieved by comparing changes in chemical composition, FT-IR spectra, and mechanical properties of Scots pine sapwood that was heat-treated in either dry state in superheated steam or in wet state using pressurized hot water. Although preferential de-polymerization of hemicelluloses was evident for both heat-treatment techniques, the analysis of the chemical composition and FT-IR spectroscopy indicated additional re-polymerization reactions within the cell wall matrix of dry heat-treated wood. The consequent formation of covalent bonds and cross-links increased the resistance against compression loads and hindered inelastic deformation during bending. This resulted in an additional reduction in bending strength and strain energy density of dry compared to wet heat-treated wood. Re-polymerization reactions during heat-treatments of wood in dry state were suggested as the main cause for the brittle failure under bending loads, while the effect of hemicellulose-removal on brittleness was much smaller than stated previously.

Microstructural characterisation and mechanical properties of spark plasma-sintered TiB2-reinforced titanium matrix composite

ABSTRACTTitanium and titanium matrix composites, reinforced with TiB2 particles, have been synthesised by the spark plasma sintering method at 1050°C under 50 MPa pressure, using mixtures of 2.4 wt.-% TiB2 and 97.6 wt.-% Ti powders. The changes in microstructural features and mechanical properties were investigated. XRD results and SEM observations confirm the formation of TiB whiskers as a result of the reaction between Ti and TiB2. However, some unreacted TiB2 particles have remained in the composite owing to the incomplete chemical reaction between matrix and additives. The measured mechanical properties demonstrate that the increase in hardness and tensile strength with TiB2 addition is mainly attributed to the generation of TiB whiskers, increase in relative density and decrease in grain size, while the reduction in bending strength is possibly due to the plastic restraint imposed on the matrix by the TiB whiskers and unreacted TiB2 particles.

Designing an antibacterial acrylic resin using the cosolvent method -Effect of ethanol on the optical and mechanical properties of a cold-cure acrylic resin.

Antimicrobial cetylpyridinium chloride (CPC) has low miscibility with acrylic resin monomer but can be homogeneously mixed using ethanol as a cosolvent. This study investigated the effects of ethanol addition on the properties of a cold-cure acrylic resin. Ethanol was an excellent cosolvent for CPC and methyl methacrylate monomer (MMA), but the cured resin exhibited a strong change in coloration to yellow (ΔE*ab>8) and a drastically reduced bending strength (from 97 to 25 MPa) and elastic modulus (from 2.7 to 0.6 GPa) when equal volumes of ethanol and monomer were used together, possibly due to the solvation and deactivation of radicals by ethanol. However, these unfavorable effects diminished when the ethanol/MMA ratio was reduced to 0.25, and became smaller when each specimen was depressurized and excess ethanol was removed. Thus, it may be possible to develop a molecularly uniform antibacterial acrylic resin with acceptable color and strength using this simple technique.

Microfibrillated Lignocellulose Enables the Suspension-Polymerisation of Unsaturated Polyester Resin for Novel Composite Applications.

A new route towards embedding fibrillated cellulose in a non-polar thermoset matrix without any use of organic solvent or chemical surface modification is presented. It is shown that microfibrillated lignocellulose made from cellulose with high residual lignin content is capable of stabilising an emulsion of unsaturated polyester resin in water due to its amphiphilic surface-chemical character. Upon polymerisation of the resin, thermoset microspheres embedded in a microfibrillated cellulose network are formed. The porous network structure persists after conventional drying in an oven, yielding a mechanically stable porous material. In an application experiment, the porous material was milled into a fine powder and added to the polyester matrix of a glass fibre-reinforced composite. This resulted in a significant improvement in fracture toughness of the composite, whereas a reduction of bending strength and stiffness was observed in parallel.

Strength Improvement of Glass Substrates by Using Surface Nanostructures

Defects and heterogeneities degrade the strength of glass with different surface and subsurface properties. This study uses surface nanostructures to improve the bending strength of glass and investigates the effect of defects on three glass types. Borosilicate and aluminosilicate glasses with a higher defect density than fused silica exhibited 118 and 48 % improvement, respectively, in bending strength after surface nanostructure fabrication. Fused silica, exhibited limited strength improvement. Therefore, a 4-μm-deep square notch was fabricated to study the effect of a dominant defect in low defect density glass. The reduced bending strength of fused silica caused by artificial defect increased 65 % in the presence of 2-μm-deep nanostructures, and the fused silica regained its original strength when the nanostructures were 4 μm deep. In fragmentation tests, the fused silica specimen broke into two major portions because of the creation of artificial defects. The number of fragments increased when nanostructures were fabricated on the fused silica surface. Bending strength improvement and fragmentation test confirm the usability of this method for glasses with low defect densities when a dominant defect is present on the surface. Our findings indicate that nanostructure-based strengthening is suitable for all types of glasses irrespective of defect density, and the observed Weibull modulus enhancement confirms the reliability of this method.

Chemical Corrosion of Liquid-Phase Sintered SiC in Acidic/Alkaline Solutions Part 1. Corrosion in HNO3 Solution

The corrosion behavior of the liquid-phase sintered SiC (LPS-SiC) was studied by dipping in 3.53 mol/L HNO3 aqueous solution at room temperature and 70 °C, respectively. The weight loss, strength reduction and morphology evolution of the SiC specimens during corroding were revealed and also the chemical corrosion process and mechanism of the SiC specimens in the acidic solution were clarified. The results show that the corrosion of the LPS-SiC specimens in the HNO3 solution is selective. The SiC particles are almost free from corrosion, but the secondary phases of BaAl2Si2O8 (BAS) and Y2Si2O7 are corroded via an acid-alkali neutralization reaction. BAS has a higher corrosion rate than Y2Si2O7, resulting in the formation of the bamboo-leaf-like corrosion pits. As the SiC specimens etched in the HNO3 solution at room temperature for 75 days, about 80 μm thickness corrosion layer forms. The weight loss and bending strength reduction of the etched SiC specimens are 2.6 mg/cm2 and 52%, respectively. The corrosion of the SiC specimens is accelerated in the 70 °C HNO3 solution with a rate about five times bigger than that in the same corrosion medium at room temperature.

Vibrational problems of timber beams with knots considering uncertainties

A stochastic model of the dynamic behavior of sawn timber beams of Argentinean Eucalyptusgrandis is herein presented. The aim of this work was to study the influence of the timber knots in the dynamical response of timber beams. The presence of knots is known to be the main source of the lengthwise variability and reduction in bending strength and stiffness in timber beams. The following parameters of the timber knots are considered stochastic: position along the beam span and within the beam cross section, shape and dimensions. Experimental data, obtained from bending and density tests, are employed to find the timber modulus of elasticity and density. On the other hand, the characteristics of the timber knots used in the stochastic model were obtained from a visual survey performed with 25 beams of the same species. The problem of the natural vibration frequencies of the timber beam is approximated with the finite element method. Numerical results are obtained using Monte Carlo simulations (MCS). The uncertainties of the timber knot parameters and their influence are quantified with the probability density function of the frequencies. Statistical results obtained by means of MCS are compared with experimental measurements in order to assess the accuracy of the stochastic model. The present approach that gives a more realistic description of timber structures correlates better with experiments.

Bending strength and internal bond strength of wood-based boards subjected to various exposure conditions

Phenol–formaldehyde resin-bonded particleboard (PF board), methylene diphenyl diisocyanate resin-bonded particleboard (MDI board), aspen oriented strand board (aspen board), Scots pine oriented strand board (pine board), methylene diphenyl diisocyanate resin-bonded medium-density fiberboard (F-MDI board), and melamine–urea–formaldehyde resin-bonded medium-density fiberboard (F-MUF board)—six board types overall—were subjected to high relative humidity (90 %, 20 °C) or cyclic humidity of high/low relative humidity (90/45 %, 20 °C) for 5 years. The PF board and aspen board showed reduction in bending strength [modulus of rupture (MOR)] and internal bond strength (IB); however, the MDI board, pine board, F-MDI board, and F-MUF board showed almost no reduction. Furthermore, the boards were subjected to outdoor exposure and Test B (boiling for 2 h) from the Japanese Industrial Standard (JIS); the results showed large reduction in the MOR and IB of the PF board and aspen board. In contrast, outdoor exposure did not greatly reduce the MOR and IB of the F-MUF board and F-MDI board. Although the IB of the F-MUF board reduced after the JIS Test B because of using low-durability resin, the IB retention was as high as 87.8 % for 5-year outdoor exposure.

Flexural properties of z-pinned composite laminates in seawater environment

Unidirectional carbon-fibre reinforced composite laminates with and without z-pins were immersed in artificial seawater and exposed to two different temperature levels (−1.75 and 50 °C), as well as thaw–freeze cycles (+20/−20 °C). The investigation described is focused on the question to which degree seawater absorption, as well as bending properties are influenced by z-pin reinforcement. The results indicate an increasing influence of the z-pin reinforcement on the water sorption rate, while the sorption rate of unpinned laminates is lower. This is a result of the additional diffusion pathways of the moisture ingress into the laminate caused by the inserted z-pins which in turn change the micro-structure. Furthermore, the sorption rate depends on the immersion temperature. Laminates immersed into seawater with higher temperatures (50 °C) display a significantly higher diffusion rate than those immersed in colder seawater (−1.75 °C) or those immersed under thaw–freeze conditions (+20/−20 °C). Z-pin reinforced laminates with a unidirectional fibre orientation show a reduced bending strength by about 31 %, as well as a reduced flexural modulus by about 11 % in comparison to unpinned samples. Unpinned and z-pinned samples that were exposed to a seawater environment for 1344 h show a reduced flexural modulus depending on the immersion temperatures. As opposed to flexural modulus, flexural strength is not affected by immersion time or temperature. The overall bending strain energy that is necessary for a complete fracture of the unpinned samples under 4-point bending loads can be described with the value of the elastic bending strain energy. In contrast to this the overall bending strain energy of the z-pinned laminates is composed of two different components –the elastic bending strain energy and the post-fracture strain energy. The post-fracture strain energy occurs after exceeding the flexural strength. The overall bending strain energy of z-pinned and unpinned samples without immersion into seawater is around 7.2 J, while the percentage of the post-fracture energy of the pinned samples is 40 % with respect to the overall bending strain energy. The duration of the immersion into water and higher water temperatures increases the overall bending strain energy for both unpinned and pinned samples. The increase is higher for z-pinned samples and is mainly caused by the increase of the post-fracture energy.

Effects of heat treatment on phase contents and mechanical properties of infiltrated B4C/2024Al composites

The B4C/2024Al composites were successfully produced by pressureless infiltration method, and the effects of heat treatment on phase content and mechanical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and mechanical properties testing. The results show that phases of B4C/2024Al composites include B4C, Al, Al3BC, AlB2 and Al2Cu. The phase species remain unchanged; however, the phase content of the composites changes significantly after heat treatment at the temperature of 660, 700, 800 or 900 °C for 12, 24 or 36 h. It is found that the heat treatment results in not only considerable enhancement in hardness, but also reduction in bending strength of the composites. Heat treatment at 800 °C for 36 h does best to hardness of the composites, while at 700 °C for 36 h it is the most beneficial to their comprehensive mechanical properties.

Effect of hydroxyapatite with different morphology on the crystallization behavior, mechanical property and in vitro degradation of hydroxyapatite/poly(lactic-co-glycolic) composite

This work describes the effect of hydroxyapatite with different morphology of nano-particle (n-HA) and whisker (w-HA) on the properties of hydroxyapatite/poly-lactic-co-glycolic acid (HA/PLGA) composite. The crystallization behavior, mechanical property and in vitro degradation of HA/PLGA composite were studied by scanning electron microscope, differential scanning calorimeter, polarized optical microscopy, electromechanical universal tester and soaking in simulated body fluid (SBF) at 37 °C for 2, 4, 8, 12 and 16 weeks, comparing with pure PLGA. The results showed that n-HA had better mechanical increment effect for PLGA than w-HA, because of the more uniformly dispersion in PLGA matrix without any cavities and the better promotion crystallization effectiveness in HA/PLGA composite than w-HA. However, the in vitro degradation showed that w-HA could keep denser microstructure so that the w-HA/PLGA composite had lower bending strength reduction percent than the n-HA/PLGA composite, owing to the higher crystallinity of w-HA and the more perfectly microcrystalline of PLGA (PLGA/w-HA) than n-HA. The study would be of guidance to select the suitable filler for poly(lactic acid) (PLA) or PLGA polymers in manufacturing bone fracture internal fixation material in future.

Mechanical properties of heat-treated wooden material utilized in the construction of outdoor sitting furniture

The present study examined the bending moment capacity and rigidity of T-type out-of-plane furniture joints and investigated the effects of heat treatment, wood species, and joint type factors on these joints. Heat treatment method clearly decreased the modulus of rupture (MOR) and the modulus of elasticity (MOE) of selected wood species. The bending strength of wood samples was reduced after the heat treatment, decreasing with increased loss of mass. For the heat-treated T-type joints, maximum bending strength values were obtained with Iroko (Chlorophora excelsa) for both mortise and tenon (MT) joints and blind MT (BMT) joints. The lowest reduction in bending strength was observed in Ash (Fraxinus excelsior L.) constructed with MT joints and with BMT joints. In general, the BMT joint had higher bending strength than MT joints. The best rigidity constant (7.21) was obtained with control Iroko BMT joints, while the worst rigidity constant (15.10) was obtained with control Oriental spruce (Picea orientalis L.) MT joints. In terms of heat-treated samples, the best rigidity constant (7.59) was obtained with Black pine (Pinus nigra L.) MT joints, while the worst rigidity constant (14.01) was obtained with Oriental spruce BMT joints. The maximum performance in joint stiffness was determined for Iroko sample BMT joints and Iroko MT joints. Lowest reduction in joint stiffness was observed in Scotch pine MT joints and Ash BMT joints. Heat treatment, wood type, and joint type had a significant effect on the bending strength of T-type MT post-rail joints. BMT joints produced from heat-treated Iroko wood can be considered as the most durable T-type joint for outdoor sitting furniture construction.

Degradation behavior of hydroxyapatite/poly(lactic-co-glycolic) acid nanocomposite in simulated body fluid

To investigate the effect of hydroxyapatite(HA) on the degradation behavior of hydroxyapatite/poly(lactic-co-glycolic) acid (HA/PLGA) nanocomposite, the degradation experiment of n-HA/PLGA composite and pure PLGA were carried out by soaking in simulated body fluid(SBF) at 37°C for 1, 2, 4 and 6 months. The change of intrinsic viscosity, thermal properties, inner structure, bending strength reduction, surface morphology and the surface deposit of n-HA/PLGA composite and pure PLGA with respect to the soaking time were investigated by means of UbbeloHde Viscometer, differential scanning calorimeter (DSC), scanning electron microscope(SEM), electromechanical universal tester, a conventional camera and X-ray diffraction (XRD). The results showed that n-HA played an important role in improving the degradation behavior of n-HA/PLGA composite, which can accelerate the degradation PLGA and endow it with bioactivity, after n-HA was detached from PLGA during the degradation, so that n-HA/PLGA composite may have a more promising prospect of the clinical application than pure PLGA as bone fracture internal fixation materials.

Sheep model for osteoporosis: Sustainability and biomechanical relevance of low turnover osteoporosis induced by hypothalamic–pituitary disconnection

Hypothalamo-pituitary disconnection (HPD) leads to low bone turnover and osteoporosis in sheep. To determine the sustainability of bone loss and its biomechanical relevance, we studied HPD-sheep 24 months after surgery (HPD + OVX-24) in comparison to untreated control (Control), ovariectomized sheep (OVX), and sheep 12 months after HPD (HPD + OVX-12). We performed histomorphometric, HR-pQCT, and qBEI analyses, as well as biomechanical testing of all ewes studied. Twenty-four months after HPD, histomorphometric analyses of the iliac crest showed a significant reduction of BV/TV by 60% in comparison to Control. Cortical thickness of the femora measured by HR-pQCT did not change between 12 and 24 months after HPD but remained decreased by 30%. These structural changes were caused by a persisting depression of osteoblast and osteoclast cellular activity. Biomechanical testing of the femora showed a significant reduction of bending strength, whereas calcium content and distribution was found to be unchanged. In conclusion, HPD surgery leads to a persisting low turnover status with negative turnover balance in sheep followed by dramatic cortical and trabecular bone loss with consequent biomechanical impairment.

A Simple Effective Flaw Model on Analyzing the Nanofiller Agglomeration Effect of Nanocomposite Materials

A special mechanics/material phenomenon involving nanocomposites is the agglomeration of nanofillers at high volume fractions of nanofillers. Numerous experimental investigations on nanocomposites have indicated a significant decrease in mechanical properties, due to the agglomeration of nanofillers. This paper describes a simple effective flaw model to correlate the local mechanical behavior of agglomerated nanoparticles with the change in global strengths of nanocomposites. The estimated bending strength reduction from our model is shown to be similar to experimental results reported by previous researchers. These results can be used as a guide for future nanocomposite design and development. Future nanomaterial manufacturing should be focused on eliminating the largest agglomerates, rather than limiting the nanofiller volume fraction. Meanwhile, by reducing the nanofiller agglomerate size, we expect that a high critical nanofiller volume fraction could be obtained to delay the mechanical property reduction.

Geometrical Effects of Pitting Corrosion on Strength and Deformability of Steel Rectangular Plates Subjected to Uniaxial Tension and Pure Bending

Strength and deformability of steel plates for marine use are studied from the viewpoint of geometry of corrosion pits. In the present study, the effect of actual pit shapes has been investigated by the non-linear, large deformation and three-dimensional finite element analyses for simulated corrosion surfaces generated by a probabilistic model of corrosion process. The tensile strength of corroded plates with semi-ellipsoidal pits is found to be estimated by the empirical formula obtained from that with conical pits,where the estimation is based on the minimum cross sectional area of the plate. The deformability of the corroded plates subjected to uniaxial tension could be estimated by the surface roughness represented by the difference of averaged plate thickness and that at the section of minimum cross sectional area. This study also shows that the reduction of the bending strength due to semi-ellipsoidal pitting corrosion is higher than that of compressive/shear/tensile strength. An empirical formula for the reduction of bending strength due to semi-ellipsoidal pits is proposed which can be a useful tool for condition assessment of aged marine structures.

Mechanical properties of ZrB 2–SiC(ZrSi 2) ceramics

Mechanical properties of ZrB 2–SiC and ZrB 2–ZrSi 2–SiC ceramics in the temperature range from 20 to 1400 °C were studied. It was found that the introduction of zirconium silicide resulted in pore-free ceramics having bending strengths of 400–500 MPa over a wide range of boride–carbide compositions. Zirconium silicide additive did not lead to significant strength and hardness changes at low temperature, but essentially increased Weibull modulus, and, therefore, the reliability of the ceramics. However, zirconium silicide additions resulted in noticeably reduced bending strength in ZrB 2–SiC based composites at 1400 °C.