Significant Loss Of Strength Research Articles

Reducing machining distortion in AA 6061 alloy through re-heating technique

Solution-treated AA 6061 alloy contains residual stresses which cause unwanted deformation during the machining operation rendering the parts unacceptable for use. Usually for AA 6061 alloy, stress relieving is performed by re-heating the parts at 343°C for 1 h. This stress relieving is however accompanied by a considerable loss of material strength which subsequently reduces the functionality of the parts. This paper is based on an effort to evaluate the effectiveness of lower re-heating temperatures for stress relieving without significant loss of strength. Temperatures within the range of 200–343°C were used and treated samples were tested for both the strength and machining distortion. The experimental results indicate 60% reduction in machining distortions with 21% decrease in the strength.

Evaluation of fire performance of prefabricated concrete buildings in Turkey

Two different large-scale industrial structures that were destroyed by fires in 2011 and 2012 in Turkey were examined. The structural framework in the first structure was constructed as prefabricated concrete, while a prefabricated concrete–steel (hybrid) was the structural framework in the second. The post-fire performance of the structures was evaluated according to the structural system properties of the buildings and tests on concrete core and steel reinforcement samples obtained from the structures. Since the fire durations of the two buildings examined were slightly different, in addition to the structural framework differences, material test results were comparatively interpreted for the two structures. The concrete used in the building exposed to the longer fire duration suffered a substantial loss in mechanical properties, the concrete cover in the reinforced concrete elements failed completely, and there was a significant loss in the yield strength of the steel reinforcement. In the second structure, which experienced a fire of shorter duration, although the concrete cover had failed similarly to the first case, there was not a substantial loss in the mechanical properties of the reinforcement and concrete. It was observed that damage to the steel structural framework in the second structure (a prefabricated concrete–steel hybrid) triggered damage in the prefabricated concrete system. The precautions that need to be taken in terms of fire, especially in industrial structures, were evaluated based on either the load-carrying system or the section, and suggestions for improvements are made.

Cyclic Behavior of Iron Ore Fines on Board Bulk Carriers: Scale Model Analysis

Solid bulk cargoes have been known to liquefy in the holds of bulk carriers since the loss of the Bengal in 1910. Because of the increased demand for iron ore fines over the past 20 years, export industries have experienced further incidents where liquefaction of the cargo was the suspected cause. The objective of this study was to develop a scale model of bulk carrier hold in order to investigate the variability of the physical properties of iron ore fines, which govern the liquefaction potential under cyclic loading. Additionally, by associating the theory of liquefaction of partially saturated soils to the cyclic behaviour of the samples, the apparent shear strength of the samples can be determined. During this study a scale model and an iron ore fines plunger were developed and utilised. The physical properties of the samples of iron ore fines were monitored during the scale model test, and the point at which moisture migration began to occur was determined. The boundary where the material showed a significant loss of shear strength, referred to as the critical failure curve, was also determined using the iron ore fines plunger. After consistent results were shown using both methods, the moisture content at which the sample was considered potentially liquefiable was concluded and compared with the results from the current test method used to reduce liquefaction incidents on bulk carriers.

Processing of polyethylene terephthalate fiber reinforcement to improve compatibility with constituents of GFRP nanocomposites

ABSTRACTThe aim of the present research was to improve the impact strength of epoxy-based glass fiber-reinforced nanocomposites by the addition of polyethylene terephthalate (PET) fibers as reinforcement along with nanoclay. Hybrid nanocomposites containing clay as nano-filler and PET fibers as micro-reinforcement were fabricated. Nanocomposites with 1 phr clay and varying concentrations of PET fibers (1–3 phr) were processed using a vacuum-assisted hand layup. Addition of untreated PET fibers did not improve the impact strength of nanocomposites due to the lack of interaction between the inert PET fibers and other constituents. To improve the interfacial interaction, two different compatibilization procedures for the surface modification of PET fibers were used. In the first procedure, silane treatment of fibers was performed using two separate silane agents. In the second method, maleic anhydride (MAH) grafting was performed in the presence of ultraviolet radiations. Compatibilization of fibers was confirmed with scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and Fourier transform infrared spectroscopy (FTIR). The results of impact and tensile testing showed an improvement of 19% in the impact strength of nanocomposites at 2 phr silane-treated PET fiber loading without significant loss in tensile strength. Finally, scanning electron micrographs of various nanocomposites were analyzed to correlate with the improved impact strength.

Central Factors Contribute to Knee Extensor Strength Loss after 2000-m Rowing in Elite Male and Female Rowers.

Despite growing interest in task-dependent alterations of central and peripheral fatigue after endurance exercise, little is known about the effect of rowing on quadriceps muscle fatigue. This study aimed to investigate central and peripheral mechanisms of fatigue after a 2000-m rowing time trial. Eight competitive rowers (four males and four females, 20 ± 4 yr) performed a 2000-m time trial on an indoor rower and a control condition (sitting). The neuromuscular function of the knee extensors was analyzed before and 3 min after each experimental condition. Maximal voluntary torque, voluntary activation, and normalized root-mean-square of the EMG signal were measured during isometric and concentric contractions. Furthermore, knee extensor twitch torque and maximal M-wave amplitudes in response to electrical nerve stimulation were assessed. After the 2000-m rowing, there were significant reductions in isometric and concentric maximal voluntary torque of the knee extensors (-20% ± 9% and -18% ± 7%, respectively, P < 0.01). Both the voluntary activation of the knee extensors during isometric and concentric contractions decreased by 18% ± 15% (P < 0.05, respectively). The normalized muscle activity of rectus femoris was significantly reduced after rowing (P = 0.007), whereas vastus medialis and vastus lateralis muscle activities did not significantly differ from baseline values. No significant change was observed for knee extensor twitch torque in response to paired electrical stimuli after rowing. The 2000-m rowing time trial resulted in significant knee extensor strength loss. Quadriceps muscle fatigue after high-intensity rowing exercise was explained primarily by central factors that lead to large reductions in voluntary drive.

Numerical Investigation of the Fracture Mechanism of Defective Graphene Sheets.

Despite the unique occurrences of structural defects in graphene synthesis, the fracture mechanism of a defective graphene sheet has not been fully understood due to the complexities of the defects. In this study, the fracture mechanism of the monolayer graphene with four common types of defects (single vacancy defect, divacancy defect, Stone–Wales defect and line vacancy defect) were investigated systematically for mechanical loading along armchair and zigzag directions, by using the finite element method. The results demonstrated that all four types of defects could cause significant fracture strength loss in graphene sheet compared with the pristine one. In addition, the results revealed that the stress concentration occurred at the carbon–carbon bonds along the same direction as the displacement loading due to the deficiency or twist of carbon–carbon bonds, resulting in the breaking of the initial crack point in the graphene sheet. The fracture of the graphene sheet was developed following the direction of the breaking of carbon–carbon bonds, which was opposite to that of the displacement loading.

Effect of Pitching Consecutive Days in Youth Fast-Pitch Softball Tournaments on Objective Shoulder Strength and Subjective Shoulder Symptoms

Background: The windmill pitching motion has been associated with risk for shoulder injury. Because there are no pitching limits on youth fast-pitch softball pitchers, these athletes often pitch multiple games across consecutive days. Strength changes, fatigue levels, and shoulder pain that develop among female fast-pitch pitchers over the course of consecutive days of pitching have not been investigated. Hypothesis: Over the course of 2- and 3-day fast-pitch softball tournaments, pitchers will develop progressive objective weakness and increased subjective shoulder fatigue and pain without complete recovery between days. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Fourteen female fast-pitch softball pitchers between the ages of 14 and 18 years were evaluated for strength and fatigue changes across 2- and 3-day tournaments. At the beginning and end of each day of tournament play, pitchers were asked to quantify shoulder fatigue and shoulder pain levels of their dominant throwing arm using a 10-point visual analog scale (VAS). Shoulder abduction, flexion, external rotation, internal rotation, elbow flexion, and elbow extension strength measurements were gathered using a handheld dynamometer. Results: Over the course of an average single day of tournament participation, pitchers developed significant increases in VAS scores for shoulder fatigue (median, 2.0; 95% CI, 1.3-3.0) and pain (median, 1.3; 95% CI, 0.5-2.3) and significant strength loss in all tested motions. Pitchers also developed significant increases in VAS shoulder fatigue (median, 3.5; 95% CI, 1.5-5.5), VAS shoulder pain (median, 2.5; 95% CI, 1.0-4.5), and strength loss in all tested motions over the entire tournament. Shoulder pain, fatigue, and strength do not fully recover between days. The accumulation of subjective shoulder pain and fatigue over the course of tournament play were closely correlated. Conclusion: Among youth female fast-pitch softball pitchers, there is a progressive increase in shoulder fatigue, pain, and weakness over the course of 2- and 3-day tournaments without full recovery between consecutive days of pitching.

ACL injury reduces satellite cell abundance and promotes fibrogenic cell expansion within skeletal muscle.

Anterior cruciate ligament (ACL) injuries are associated with significant loss of strength in knee extensor muscles that persists despite physical therapy. The underlying mechanisms responsible for this protracted muscle weakness are poorly understood; however, we recently showed significant myofiber atrophy and altered muscle phenotype following ACL injury. We sought to further explore perturbations in skeletal muscle morphology and progenitor cell activity following an ACL injury. Muscle biopsies were obtained from the injured and non-injured vastus lateralis of young adults (n = 10) following ACL injury, and histochemical/immunohistochemical analyses were undertaken to determine collagen content, abundance of connective tissue fibroblasts, fibrogenic/adipogenic progenitor (FAP) cells, satellite cells, in addition to indices of muscle fiber denervation and myonuclear apoptosis. The injured limb showed elevated collagen content (p < 0.05), in addition to a greater abundance of fibroblasts and FAPs (p < 0.05) in the injured limb. Fibroblast content was correlated with increased accumulation of extracellular matrix in the injured limb as well. A higher frequency of interstitial nuclei were positive for phospho-SMAD3 in the injured limb (p < 0.05), providing some evidence for activation of a fibrogenic program through transforming growth factor β following an ACL injury. The injured limb also displayed reduced satellite cell abundance, increased fiber denervation and DNA damage associated with apoptosis (p < 0.05), indicating alterations within the muscle itself after the ligament injury. Injury of the ACL induces a myriad of negative outcomes within knee extensor muscles, which likely compromise the restorative capacity and plasticity of skeletal muscle, impeding rehabilitative efforts. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1876-1885, 2017.

Evaluation of the effect of processing conditions on the impact properties of polypropylene-nano-CaCO3 composites

Processing variables are known to have a decisive influence on the impact properties of polypopylene-nano-CaCO3 composites. Therefore, it becomes mandatory to evaluate the effect of extrusion conditions on composite impact resistance. In the present work, a response surface methodology was used to evaluate the effects of screw rotation speed, screw configuration, and nanoparticles content on the polypropylene impact properties. The concentration of the nano-CaCO3 particles, the screw rotation speed, and the interaction between these entrance factors were the processing variables of greater influence on the impact properties of nano-CaCO3/polypropylene composites. The increase of screw rotation speed led to a decrease in the impact resistance, while the increase of filler content promoted an increase of such property. However, the increase of nanoparticles content led to obtaining poor tensile properties. Therefore, the filler content has to be adjusted in order to improve the impact properties without significant loss of mechanical strength.

Effect of bone bank processing on bone mineral density, histomorphometry & biomechanical strength of retrieved femoral head.

Background & objectives:Standard processing of the bone grafts involves deep-freezing and sterilization with gamma irradiation which may alter mechanical properties of the bone graft. This study was aimed at measuring the effect of bone bank processing on the mechanical properties of bone allograft and its correlation with bone mineral density [BMD, dual-energy X-ray absorptiometry (DEXA Scan)] and histomorphometric indices.Methods:Femoral heads retrieved from patients undergoing hip replacement surgeries were used as the material. Twenty femoral heads were under taken in the study. Each femoral head was cut into two equal cubes. One cube was subjected to BMD measurement using DEXA Scan followed by unilateral compression test. Histomorphometric indices such as trabecular number (Tb. N.), trabecular separation (Tb. S.), trabecular thickness (Tb. T.) and bone volume (B.V.) were calculated on the same specimen by a computer software. The other cube was kept in deep freezer (−76°C) for a minimum of three weeks, followed by gamma irradiation and subjected to similar tests.Results:Results were compared in pre- and post-processed bone specimens. A significant loss of biomechanical strength (P<0.001) with mean a loss of 18.90 per cent was found in post-processed samples in uniaxial compression tests. Similarly, BMD (mean decrease by 13.8%, P<0.01) and histomorphometric indices such as Tb. T. (mean decrease by 12.37%, P<0.01), Tb. S. (mean increase by 12.60%, P<0.001) and B.V. (mean decrease by 20.84%, P<0.01) were found. However, Tb. N. was not significantly affected.Interpretation & conclusions:The current method of processing of bone allografts i.e. deep-freezing and gamma irradiation appeared to cause a significant reduction in the biomechanical strength of allogenic bone which was more suitable to be use in the morselized form. Appropriate consideration for decreased strength needs to be given when using allogenic bone graft as a structural graft.

Effects of high energy radiation and thermo-chemical environments on polyetherimide composites: futuristic approach to nuclear waste storage

This research highlights the effect of radiation, chemical and thermal environments on mechanical and thermal properties of polyetherimide (PEI) composites. The tests are conducted on specimens made from PEI and PEI reinforced with modified Carbon Nano Fibre (CNF). The specimens are subjected to gamma radiation doses of 5 MGy, which is equivalent to the cumulative dose of radiation from spent nuclear fuel until the end of complete radioactivity. The exposed samples are further subjected to highly corrosive and thermal environments. Studies under transmission electron microscopy reveal that there is a uniform dispersion of modified CNF in PEI. Differential Scanning Calorimetry (DSC) and Thermo Gravimetric Analysis (TGA) indicate that there are no significant changes in thermal properties of PEI and PEI composite when exposed to aggressive environments. It is observed that there is a marginal loss in the tensile strength of polymeric samples when exposed to gamma radiation and thermal environments. PEI samples when subjected to alkaline corrosive environments show significant loss in the tensile strength. There is a significant decrease in the molecular weight of PEI under alkaline corrosive environments as seen from Gel Permeable Chromatography (GPC).

Oxidation Behavior of Matrix Graphite and Its Effect on Compressive Strength

Matrix graphite (MG) with incompletely graphitized binder used in high-temperature gas-cooled reactors (HTGRs) is commonly suspected to exhibit lower oxidation resistance in air. In order to reveal the oxidation performance, the oxidation behavior of newly developed A3-3 MG at the temperature range from 500 to 950°C in air was studied and the effect of oxidation on the compressive strength of oxidized MG specimens was characterized. Results show that temperature has a significant influence on the oxidation behavior of MG. The transition temperature between Regimes I and II is ~700°C and the activation energy (Ea) in Regime I is around 185 kJ/mol, a little lower than that of nuclear graphite, which indicates MG is more vulnerable to oxidation. Oxidation at 550°C causes more damage to compressive strength of MG than oxidation at 900°C. Comparing with the strength of pristine MG specimens, the rate of compressive strength loss is 77.3% after oxidation at 550°C and only 12.5% for oxidation at 900°C. Microstructure images of SEM and porosity measurement by Mercury Porosimetry indicate that the significant compressive strength loss of MG oxidized at 550°C may be attributed to both the uniform pore formation throughout the bulk and the preferential oxidation of the binder.

DEVELOPED PROBABILISTIC REDUCTION FACTORS FOR LOPHIRA ALATA (EKKI) TIMBER JOISTS SUBJECTED TO CREEP-RUPTURE

Wood experiences a significant loss of strength and stiffness when loaded over period of time. This phenomenon is known as creep-rupture. Several models were developed for the estimation of the reduction of load carrying capacity of timber with time. In this paper, the results of time dependent structural reliability analysis of timber joist produced with Lophiraalata (Ekki) timber specie was presented. Three load duration models were considered in the study, namely: The Model proposed by Wood, Gerhards model, and Nielsen. The timber joist was designed in accordance with the Eurocode 5. The uncertainties in all the basic design variables were fully accommodated in the time dependent reliability analysis. The entire process was implemented using a developed MATLAB program employing First Order Reliability Method (FORM). Time dependent mathematical models for modification of safety index to account for the effect of load duration were proposed. The use of both Gerhards and Nielsen model, for the design of Lophiraalata timber members was recommended. http://dx.doi.org/10.4314/njt.v36i1.6

DEVELOPED PROBABILISTIC REDUCTION FACTORS FOR LOPHIRA ALATA (EKKI) TIMBER JOISTS SUBJECTED TO CREEP-RUPTURE

Wood experiences a significant loss of strength and stiffness when loaded over period of time. This phenomenon is known as creep-rupture. Several models were developed for the estimation of the reduction of load carrying capacity of timber with time. In this paper, the results of time dependent structural reliability analysis of timber joist produced with Lophiraalata (Ekki) timber specie was presented. Three load duration models were considered in the study, namely: The Model proposed by Wood, Gerhards model, and Nielsen. The timber joist was designed in accordance with the Eurocode 5. The uncertainties in all the basic design variables were fully accommodated in the time dependent reliability analysis. The entire process was implemented using a developed MATLAB program employing First Order Reliability Method (FORM). Time dependent mathematical models for modification of safety index to account for the effect of load duration were proposed. The use of both Gerhards and Nielsen model, for the design of Lophiraalata timber members was recommended. http://dx.doi.org/10.4314/njt.v36i1.6

Microencapsulated phase change materials for enhancing the thermal performance of Portland cement concrete and geopolymer concrete for passive building applications

Concretes with a high thermal energy storage capacity were fabricated by mixing microencapsulated phase change materials (MPCM) into Portland cement concrete (PCC) and geopolymer concrete (GPC). The effect of MPCM on thermal performance and compressive strength of PCC and GPC were investigated. It was found that the replacement of sand by MPCM resulted in lower thermal conductivity and higher thermal energy storage, while the specific heat capacity of concrete remained practically stable when the phase change material (PCM) was in the liquid or solid phase. Furthermore, the thermal conductivity of GPC as function of MPCM concentration was reduced at a higher rate than that of PCC. The power consumption needed to stabilize a simulated indoor temperature of 23°C was reduced after the addition of MPCM. GPC exhibited better energy saving properties than PCC at the same conditions.A significant loss in compressive strength was observed due to the addition of MPCM to concrete. However, the compressive strength still satisfies the mechanical European regulation (EN 206-1, compressive strength class C20/25) for concrete applications. Finally, MPCM-concrete provided a good thermal stability after subjecting the samples to 100 thermal cycles at high heating/cooling rates.

High-Volume Municipal Solid Waste Incineration Bottom Ash Concrete

About 50 % of Municipal Solid Waste is incinerated (MSWI) in Europe what represent ca. 50 Mt/a of MSWI bottom ash (BA). Bottom ash contains several marketable components (iron scrap, non-ferrous metals, glass) which can by separated from the main BA stream and placed on the market with secondary sources. The resting material is, by its composition and properties, similar to natural aggregates and can be used in this way. The influence of metals separation form BA on its behavior in concrete was tested by using BA from Praha Malešice Waste-to-Energy plant. particle size fractions 4/8 and 8/16 mm of this BA can be used as aggregates in concrete up to 50 vol. % of given fraction without any significant loss of concrete strength. The combination of valuable component separation form BA and recycling of the rest portion as aggregates feature promising way of BA management reducing the amount of BA to be landfilled to minimum.

Outcomes After Surgical Treatment of Adolescent Intra-articular Distal Humerus Fractures.

To determine the radiographic and clinical outcomes of the surgical management of adolescent intra-articular distal humerus fractures. We performed a retrospective review of the clinical and radiographic outcomes of 31 consecutive adolescent patients surgically treated for acute distal humerus intra-articular fractures. Nine patients returned for objective measures of range of motion, strength testing, and completion of validated outcome scores including the Mayo Elbow Performance Score (MEPS); The Disabilities of the Arm, Shoulder, and Hand Score (DASH); and the SF-36. The average age at the time of injury was 13.5 years (range, 12 to 16 y) with a mean follow-up of 1.22 years (range, 9 d to 5.5 y). Multiple surgical approaches were performed. Overall, the active range of motion for our patients was 10.7 to 133.9 degrees with a mean arc of 123.4 degrees. AO classification type C2 and C3 injuries lost significantly more motion than other fracture patterns. Twelve patients sustained perioperative nerve palsies that resolved by final follow-up; seven of these nerve injuries were iatrogenic and sustained during a Bryan-Morrey tricepital slide approach. Eight patients required implant removal; 7 of these patients had prominent olecranon screws after an olecranon osteotomy. Including postoperative neuropathies, there were 20 complications in 15 patients. Thirteen complications in 9 patients required a return to the operating room. Of the 9 patients who returned for objective testing, there was no statistically significant loss of range of motion or strength of the injured extremity when compared with the uninjured limb. The MEPS revealed 6 excellent, 1 good, and 2 fair results. The average DASH score was 5.1 (range, 0 to 19.1) and the physical (average 55.7; range, 47.4 to 59.0) and mental components (average 54.2; range, 29.8 to 63.4) of the SF-36 were comparable. After surgical intervention for an adolescent intra-articular distal humerus fracture, one can expect no significant loss of motion or strength. The reported outcomes are not all excellent. The peri-operative complication rates are high and may be related to surgical approach and fracture pattern. Level IV.

Enhancing plasticity of high-strength titanium alloys VT 22 under impact-oscillatory loading

The purpose of this paper is to provide new experimental data for high-strength VT 22 titanium α + β-type alloy under impact-oscillatory loading and dynamic non-equilibrium process. Based on the performed experimental studies, it was found that overall plastic deformation of this alloy can be increased by a factor 2.75 compared with its initial state without significant loss of strength. To achieve this goal, a new methodology to study the impact behaviour of materials under non-equilibrium process has been used. Physical research revealed that significant microstructural refinement of the alloy is observed after such type of loading, as the result of which the fine grains are formed with subgrain refinement which takes place within the basis of alloy.

Membrane-Based Gas Separation Accelerated by Hollow Nanosphere Architectures.

The coupling of hollow carbon nanospheres with triblock copolymers is a promising strategy to fabricate mixed-matrix membranes. This is because the symmetric microporous shells combine with the hollow space to promote gas transport, and the unique soft-rigid molecular structure of triblock copolymers can accommodate a high loading of fillers without a significant loss of mechanical strength.

Antiwrinkle Finishing of Cotton Fabrics with 5-(Carbonyloxy succinic)-benzene-1,2,4-tricarboxylic Acid: Comparison with Other Acids

5-(Carbonyloxy succinic)-benzene-1,2,4-tricarboxylic acid (BSTA) was synthesized and applied as an effective cross-linking agent for cotton fabrics. In this study, BSTA was analyzed and compared with two other extensively investigated poly(carboxylic acid)s, 1,2,3,4-butanetetracarboxylic acid (BTCA) and 3,3′4,4′- benzophenone tetracarboxylic acid (BPTCA), in cross-linking cellulose. Possessing both aromatic and aliphatic carboxylic acid groups and respective properties, BSTA can cross-link cellulose as efficiently as BTCA without causing significant loss of tensile strength of the products. In addition, BSTA exhibits better hydrophilicity and higher affinity to cellulose than the aromatic acid. BSTA is able to produce anhydride under high temperature but it is not a rate-determining step in the esterification process. The kinetic data of BTCA, BPTCA, and BSTA with cellulose were calculated by measuring the concentrations of the carboxylic acids on the fabric, showing an order of BPTCA< BSTA< BTCA in react...