Reduction In Bending Strength Research Articles

Wood Degradation after Windthrow in a Northern Environment

Severe windthrows often require salvage operations that can lead to increased costs. Given these extra costs, it is of paramount importance to make sure that wood degradation does not become so advanced that significant value loss is incurred. The rate at which wood deteriorates is a function of many factors, including species and climate. The study was conducted in a northern area affected by two partial windthrows. Logs from the damaged area were collected for two species, balsam fir (Abies balsamea) and black spruce (Picea mariana). Logs were classified into one of three degradation classes based on visual assessments. A sample of logs from standing trees was also collected. In total, 167 logs were sampled. Each log was sawn and one piece of lumber was selected from each to determine the bending strength and stiffness and the visual grade. The time since tree death, as determined from dendrochronology, ranged from 1 to 31 years. The visual grade of the lumber was not affected after 1 year but severe downgrades were observed after 4 years. Moisture content decreased rapidly for both species during the first year and continued to decrease until 4 years after mortality. No clear decrease in bending stiffness was identified even though such a tendency was noticed for older black spruce windthrows. Bending strength became variable after 4 years for balsam fir and was reduced after 4 years for black spruce. Windthrows older than 7 years will produce low visual grade timber of reduced bending strength and possibly of lower bending stiffness.

One Year of Transgenic Overexpression of Osteoprotegerin in Rats Suppressed Bone Resorption and Increased Vertebral Bone Volume, Density, and Strength

RANKL is an essential mediator of bone resorption, and its activity is inhibited by osteoprotegerin (OPG). Transgenic (Tg) rats were engineered to continuously overexpress OPG to study the effects of continuous long-term RANKL inhibition on bone volume, density, and strength. Lumbar vertebrae, femurs, and blood were obtained from 1-yr-old female OPG-Tg rats (n = 32) and from age-matched wildtype (WT) controls (n = 23). OPG-Tg rats had significantly greater serum OPG (up to 260-fold) and significantly lower serum TRACP5b and osteocalcin compared with WT controls. Vertebral histomorphometry showed significant reductions in osteoclasts and bone turnover parameters in OPG-Tg rats versus WT controls, and these reductions were associated with significantly greater peak load in vertebrae tested through compression. No apparent differences in bone material properties were observed in OPG-Tg rat vertebrae, based on their unchanged intrinsic strength parameters and their normal linear relationship between vertebral bone mass and strength. Femurs from OPG-Tg rats were of normal length but showed mild osteopetrotic changes, including reduced periosteal perimeter (-6%) and an associated reduction in bending strength. Serum OPG levels in WT rats showed no correlations with any measured parameter of bone turnover, mass, or strength, whereas the supraphysiological serum OPG levels in OPG-Tg rats correlated negatively with bone turnover parameters and positively with vertebral bone mass and strength parameters. In summary, low bone turnover after 1 yr of OPG overexpression in rats was associated with increased vertebral bone mass and proportional increases in bone strength, with no evidence for deleterious effects on vertebral material properties.

Evaluation of the Physical and Mechanical Properties of Medium Density Fiberboard Made from Old Newsprint Fibers

The goal of this study was to investigate the use of old newsprint (ONP) fiber as raw material for laboratory made medium density fiberboard (MDF). Effect of ONP fiber mixed with virgin aspen (Populus deltoides) fiber and the press time (3, 4, and 5 min) on the properties of MDF panels were determined. Panels were produced using aspen fibers in surface layer and combination of aspen fibers and ONP fibers in core layer. Physical (thickness swelling) and mechanical properties of the panels were determined according to the procedure of EN standards. This study showed reduction in bending strength and internal bond strength of the panels as ONP fiber was loaded from 35 to 70% in core layer. Thickness swelling of MDF panels was drastically increased with addition of ONP fiber to the panels’ furnishes. Based on the findings of this study, it appears that ONP can be considered as a potentially suitable raw material for manufacturing MDF products without having any significant adverse influence on the panel properties.

Dioxin exposure in contaminated sawmill area: The use of molar teeth and bone of bank vole (Clethrionomys glareolus) and field vole (Microtus agrestis) as biomarkers

Developmental disorders of teeth are among the most sensitive targets of polychlorinated dibenzo-p-dioxin and -furan (PCDD/F) exposure. In rats, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) reduces dose-dependently the size of molars, most severely the third lower molars. Dioxins also have effects on developing bone, including altered bone mineral density as well as reduced bending breaking force and stiffness. The aim of this study was to evaluate the use of the third lower molar and long bones as biomarkers of PCDD/F exposure in two wild vole species, the bank vole (Clethrionomys glareolus) and the field vole (Microtus agrestis) collected from a PCDD/F contaminated former sawmill area. Survey of soil and biota of the sawmill area indicated a PCDD/F contamination with a congener profile characteristic for the chlorophenol wood preservative Ky-5. The PCDD/F concentration in the bank vole was notably higher than in the field vole. The third molar of the bank vole was significantly smaller in dioxin-exposed animals compared to control group, while there was no difference between these two groups in the field vole. No significant alterations were observed in bone density and strength in either species except for reduced bending strength of the femur neck in bank vole males exposed to dioxins. Even though the bone changes are among the sensitive endpoints of dioxin-exposure, high variability due to age, size and gender limits their use as biomarkers of wildlife exposure. In conclusion, the size of molar teeth seems to be a sensitive and robust biomarker for PCDD/F exposure in wild bank vole populations and thus worth of further studies.

The effect of global slope of grain on the bending strength of scaffold boards

A study is described, carried out on specially prepared specimens, that specifically examines the effect of slope of grain on the bending strength of scaffold boards. Each specimen was visually graded and both the modulus of rupture and modulus of elasticity in bending determined. From the effect of slope of grain on the reduction of bending strength revised visual grading rules have been suggested that include a slope of grain limit of 1 in 12. It has also been demonstrated that machine grading is as effective at determining the adverse effect of slope of grain on board strength as it is for other defects such as high rate of growth and knots.

Einfluss der hydrothermischen Behandlung von Pinus radiata D. Don auf ausgewählte Eigenschaften des Holzes | Influence of hydrothermal treatment of Pinus radiata D. Don on specific characteristics of the wood

Pinus radiata wood was treated under hydrothermal conditions(steam) in an autoclave. The effect of temperature and time were studied. Bending strength, equilibrium moisture content, swelling and pH value of residual water were determined. Following effects were determined: a) a reduction of pH value, b) a considerable reduction of wooden mass, c) a reduction of equilibrium moisture up to 75% air humidity was registered. With higher air humidity no differences between treatments were detected, and d) with higher temperatures and longer treatment time, a reduction of bending strength was ascertained.

Influence of Environmental Aging on Properties of Polymeric Mortars

The emergence of polymeric mortars as a class of materials with applications in civil engineering requires a systematic study of their properties, including mechanical strength and durability under severe environmental conditions. This study reports results based on tests of polymeric mortars, both with epoxy and polyester resins, after exposure to (1) immersion both in distilled and in salt water, (2) salt fog spray cycles (8 h of salt fog, followed by 16 h drying, at 35°C), and (3) temperature cycles [12 h at 20 and 50°C, respectively, with relative humidity (RH) kept at 80%]. Additional tests for humidity cycles at fixed temperature and ultraviolet rays are reported elsewhere. Moisture absorption is analyzed based on mass changes for submerged specimens and Fickian type behavior evaluated. Compressive and bending strength degradation, as well as increase of brittleness, are examined for these accelerated actions and preliminary interpretation advanced. The relative severity of the effects is graphically displayed, tabulated, and analyzed. Brittleness increases more rapidly, under salt fog, for epoxy mortar and bending strength reduction at 10,000 h is also higher (50%) for epoxy mortar than for polyester mortar (32%). Thermal cycles also provoked greater deterioration of bending strength on epoxy mortars. Compressive tests led to results of similar tendency, but with smaller differences.

Oblique bending in U-shaped steel sheet piles

U-shaped Larssen steel sheet piles are normally driven in pairs. The common interlock may be crimped or welded to prevent inter-pile movement, creating an asymmetric section which may exhibit a reduced bending strength due to oblique (biaxial) bending. The recently introduced Eurocode 3: part 5 takes this into account and applies a reduction factor on bending strength. This paper provides information on the selection of values for the reduction factor and will be of interest to designers of U-section steel sheet pile retaining walls. Experimental tests carried out on one-sixth scale U-piles are reported, together with a theoretical analysis of oblique bending. The research shows that freedom of lateral movement is important to the development of oblique bending. Furthermore, pile walls restrained against lateral movement by soil–structure interaction, among other things, will not exhibit significant oblique bending.

Oblique bending in U-shaped steel sheet piles

U-shaped Larssen steel sheet piles are normally driven in pairs. The common interlock may be crimped or welded to prevent inter-pile movement, creating an asymmetric section which may exhibit a reduced bending strength due to oblique (biaxial) bending. The recently introduced Eurocode 3: part 5 takes this into account and applies a reduction factor on bending strength. This paper provides information on the selection of values for the reduction factor and will be of interest to designers of U-section steel sheet pile retaining walls. Experimental tests carried out on one-sixth scale U-piles are reported, together with a theoretical analysis of oblique bending. The research shows that freedom of lateral movement is important to the development of oblique bending. Furthermore, pile walls restrained against lateral movement by soil–structure interaction, among other things, will not exhibit significant oblique bending.

Long bones from the senescence accelerated mouse SAMP6 have increased size but reduced whole-bone strength and resistance to fracture.

The senescence accelerated mouse strain P6 (SAMP6) has emerged as a useful model of senile osteoporosis because it has many features of the disease, including low trabecular bone formation and low areal bone density. We further characterized the SAMP6 model of senile osteoporosis by comparing morphological, mechanical, and densitometric properties of femurs and tibias from SAMP6 mice to those of the control strain (SAMR1) at 4 months and 12 months of age. SAMP6 long bones had increased periosteal width and endosteal area (p < 0.05), resulting in an average increase of 30% in moments of inertia (p < 0.05), but no difference in bone area (p > 0.05) compared with control. Despite their increased moments of inertia, long bones from SAMP6 mice were relatively weak and brittle. Ultimate bending moment was reduced by 25%, and both postyield displacement and energy-to-fracture were reduced by 60% compared with SAMR1 controls (p < 0.001). Average cortical ash fraction was increased slightly from 0.74 in SAMR1 to 0.76 in SAMP6 bones (p < 0.05), indicating that increased mineralization may have contributed to the brittleness of SAMP6 bones. The relative differences we observed--increased endosteal and periosteal dimensions, reduced bending strength, increased brittleness, and increased mineralization--are analogous to changes that occur in the aging human skeleton. Moreover, these features were consistently observed in young (4-month) and old (12-month) animals. These findings extend the previous descriptions of the SAMP6 mouse and identify key mechanical features that further validate its relevance as a unique and functionally relevant model of senile osteoporosis.

Influence of Ultrasonic Vibration Frequency on Acceleration of Hydrothermal Aging of FRP

This study deals with the accelerated hydrothermal aging test method of fiber-reinforced plastic panels by applying an ultrasonic vibration to the material. The ultrasonic vibration was applied to the specimen during or after immersion in water. The accelerated aging tests were conducted at three vibration frequencies (50 k Hz, 100 k Hz, and 200 k Hz), and the effect of the ultrasonic vibration frequency on the acceleration of aging was discussed. The effect of applying the ultrasonic vibration for the accelerated aging was evaluated from weight change measurements and the bending property. The aging was accelerated by applying the ultrasonic vibration continuously during the water immersion, and it was found that the most effective frequency of ultrasonic vibration was 50 k Hz. The ultrasonic vibration affected the acceleration of the dissolution from the interface, and as a result, the weight loss occurred at shorter immersion time compared with the ordinary immersion test. Such dissolution from the interface induced the weight gain due to the water penetration and the bending strength reduction.

橋梁用樹脂製カバーの長期健全性の評価

Firstly, the service life of the 28-year-old plastic covering material of cables for the long bridge was evaluated. Mechanical degradation such as crack generation and remarkable bending strength reduction on the plastic covering material was not found because of the past adequate maintenance for coating film layer covered on the plastic covering material. However, by means of chemical evaluation method such as FT-IR, the slight chemical degradation was confirmed and shown as follows. (1) Main molecular chains of the coating film (polyester) and side chains of base resin (PMMA) were detached by hydrolysis. (2) The glass transition temperature of the base resin was raised by polymerization. Secondly, to examine effective degradation detection methods, the degradation experiment was conducted on PMMA test samples without containing anti-oxidants and pigments in the autoclave at 70°C with saturated water and pure O2. Effective degradation detection methods were as follows: inspection with optical microscope, measurement for bending strength, dynamic hardness, dynamic viscoelasticity, FT-IR, DSC, and solid 13CNMR.

Effects of ionizing radiation on the mechanical properties of human bone.

Allogeneic bone grafts are frequently sterilized by means of ionizing radiation. We investigated the effects of ionizing radiation on both quasistatic and impact mechanical properties of human bone. Specimens from four paired femora of four donors received doses of 29.5 kGy ("standard," frequently used by tissue banks), 94.7 kGy ("high"), or 17 kGy ("low") of ionizing radiation. Young's modulus was unchanged by any level of radiation. Radiation significantly reduced bending strength, work to fracture, and impact energy absorption; in each case, the severity of the effect increased from low to standard to high doses of radiation. Work to fracture was particularly severely degraded; specimens irradiated with the high dose absorbed only 5% of the energy of the controls. Radiation, even at relatively low doses, makes the bone more brittle and thereby reduces its energy-absorbing capacity. We suggest that because the level of radiation required to produce an acceptable level of viral inactivation (90 kGy) produces an unacceptable reduction in the mechanical integrity of the bone, low levels of radiation, sufficient to produce bacterial safety, should be used in conjunction with biological tests to ensure viral safety.

Studies of blends of poly(phenylene sulfide) and a liquid crystalline polymer: Time-temperature superposition

Abstract Polymer blends containing poly(phenylene sulfide) (PPS) and liquid crystalline polymer (LCP) of varying compositions were injection molded and tested. Three-point bending tests were carried out on annealed and unannealed samples at various temperatures and strain rates. The time–temperature master curves were constructed by shifting the experimental modulus data at each point of the curves. The increase in bending modulus and reduction of bending strength with increasing LCP content were attributed to the skincore morphology. The time-temperature curves revealed that the bending modulus of the blends can be superimposed over a wide range of temperatures and strain rates.

A new type of fiber-bonded-ceramic material synthesized from pre-oxidized Si-Ti-C-O fiber

Two types of fiber-bonded-ceramic material (FBC2123 or FBC1873) were synthesized from preoxidized Si-Ti-C-O fibers with oxide layers of 150 to 500 nm in thickness at 2123 K or 1873 K under 50 to 70 MPa. The interstices in both types of the materials were packed by an oxide material, which had existed on the surface of the pre-oxidized Si-Ti-C-O fiber. So, the dense, fiber-bonded-ceramic materials with small amount of the oxide matrix were obtained. During hot-pressing, carbon in excess of the non-stoichiometric ratio was released from the fiber and formed an interfacial layer on the surface of the fiber, beneath the pre-existing oxide material. Both FBC2123 and FBC1873 showed fibrous fracture patterns with high fracture energies at temperatures up to 1573 K and 1773 K, respectively. FBC2123 exhibited some plasticity in air at a temperature of 1673 K or over, due to the existence of amorphous silica in the matrix, and then a reduction in bending strength was observed at 1773 K in air. On the other hand, FBC1873 maintained its initial bending strength up to 1773 K in air, which is attributed to reduced crystallization of Si-Ti-C-O fiber and to the formation of cristobalite in the matrix.

Experimental changes in mineral content of juvenile mouse femora.

Juvenile laboratory mice were exposed to hypergravity (8 g), burrowing exercise, swimming to exhaustion, an anabolic steroid, and swimming and an anabolic steroid for 30 days to determine the variability of skeletal mineralization during growth. Changes in mineralization were correlated with changes in bending strength. Experimental mouse femora were loaded to failure in a cantilever beam configuration to determine bending strength, and ashed to determine total mineral content. Between experimental groups, mineral content ranged from 66.0 to 71.2% with the greatest change from the control being a 4.7% decrease in mineralization in the male swimming exercise group (P less than 0.001). Within two age-matched experiments, the first showed that the group with the greatest decrease in mineralization also had the greatest reduction in bending strength (P less than 0.001). The second age-matched experiment showed that the group with the greatest reduction in mineralization had bending strength greatly reduced (P less than 0.001). However, in this experiment, the weakest femora were in the anabolic steroid group that did not have the mineral content reduced. We conclude that (1) mineralization of juvenile mouse femora is extremely variable given varied conditions of exercise or loading; (2) mineralization of normal bone is decreased more often and to a greater extent than increased from normal exercise controls; (3) the decrease in mineralization seen here can decrease bending strength; and (4) the decrease in mineralization seen was not caused by a decrease in a mechanical loading but was probably due to a corticosterone-mediated psychological stress response.(ABSTRACT TRUNCATED AT 250 WORDS)

STRENGTH CHARACTERISTICS OF CHANNEL BEAMS UNDER WARPING AND TWIST PREVENTION

The fundamental bending strength characteristics of channel section beams are studied by a numerical analysis and checked with respect to the effects of loading conditions, type of cross sections and initial imperfections. The slender type of high depth channel to be likely used in plate girder structures and the compact section type for hot-rolled shapes are adopted here. Mainly emphasized are the effects of prevention of twist at the loading point and the warping restraint at beam ends. The reduction of bending strength due to lateral-torsional buckling is significantly improved by the end warping restraint and prevention of twist at the loading point. Finally, it is concluded that the channel section beams can be used as main structural members.

潤滑下における動力伝達用ポリアセタール歯車の強度 Ｉ 鋼歯車とかみ合わせた場合

A polyacetal gear of module 2 is engaged with a steel gear coated by gear oil or grease only initial stage, and different loads are applied to the set. Bending strengths and wears of polyacetal gear teeth under lubricated conditions are compared with those obtained under unlubricated conditions. Experiments are also carried out under the conditions of forced lubrication, and similar comparative studies are made on the results. Obtained test results are summarized as follows : (1) Reduction of bending strength of gear teeth caused by temperature increase is suppressed by lubricating gears. Furthermore, it is found that the extent of reduction of bending strength of gear teeth varied according to the lubrication methods applied even under the same load. The smallest is in the case of forced oil lubrication in which large amount of oil is used, followed by the case of grease coating, and the largest is in the case of oil coating. (2) Marked improvement of allowable loads, in which wears of gear teeth are taken into consideration, are recognized under the lubricated conditions compared to those obtained under unlubricated conditions.

The effects of drying and re-wetting on some mechanical properties of cortical bone

The purpose of the work described in this note was to determine whether drying bone, and then re-wetting it, had any important effect on its mechanical properties. Bending tests were performed on cow's bone. The effect on Young's modulus was extremely small, and insignificant in these experiments. Drying and re-wetting produced a statistically significant 5% reduction in bending strength. The work under the load deformation curve was not apparently altered by the treatment, but this value had a large variance, and the effect of drying would have to be very marked to be observable. The effect of drying and re-wetting on the mechanical properties of bone tested here can probably be ignored.

Aging test and dynamic fatigue test of apatite-wollastonite-containing glass ceramics and dense hydroxyapatite.

The purpose of this study is to examine the changes in mechanical strength of two bioactive ceramics in living tissue. An aging test and dynamic fatigue test were performed using apatite-wollastonite-containing glass ceramics (A X W-GC) and dense hydroxyapatite (HA). Specimens (5 mm X 5 mm X 25 mm, abraded with No. 2000 Al2O3 powder) were implanted into subcutaneous tissue of rats for varying periods of time. The bending strength of aged samples was measured by the three-point loading method. The bending strength of A X W-GC was greater than that of HA (P less than 0.001). There was no reduction in bending strength for both A X W-GC and HA in living tissue. The n value of both A X W-GC and HA did not decrease significantly after implantation as assessed by the results of the dynamic fatigue test according to analysis of covariance. SEM-EPMA showed that Si and Mg contents decreased, Ca content did not change, while P content increased in the surface of A X W-GC. The area where x-ray intensity changed increased moderately after implantation. There were no changes in Ca and P at the interface between HA and soft tissue. In macroscopic and microscopic observations, specimens were found to be encapsulated with a thin layer of connective tissue. Foreign body giant cells, osteoblasts, or osteoclasts were not observed in the soft tissue. There was no bonding between ceramics and soft tissue.