Decrease In Ultimate Stress Research Articles

Axial compression performance of concrete-filled steel tubular columns with damaged BFRP jackets

Concrete-filled basalt fiber reinforced polymer (BFRP) -steel composite tube (CFBCT) columns have become a highly anticipated composite structure. The lateral confinement provided by BFRP can effectively suppress the possible local buckling of the steel tube, thereby achieving the goal of optimizing axial compression performance. With the widespread application of CFBCT in engineering practice, the BFRP outer layer is likely to be affected by factors such as construction accidents or connection design, resulting in slotting and drilling damage to the BFRP outer layer. Therefore, the mechanical properties of CFBCT subjected to local damage are critical. This article examined the effects of slotting and drilling the BFRP outer layer on the axial compression performance. The non-uniform strain distribution at the damaged site was analyzed using digital image correlation (DIC) testing technology. The results show that the local damage can lead to a decrease in the bearing capacity and ductility. Compared with drilling damage, slotting has a more significant impact on axial behavior. Due to the local damage, the ultimate stress decrease by 8.1 % and 12.4 % respectively. A new computational method was introduced to predict the quantitative impact of local damage on CFBCT.

Damage Evolution of Antibacterial Stainless Steel at Different Loading Rates Based on Digital Image Correlation Method

Using Shimadzu AGS‐100KN tensile machine, LEICA‐LM/DM optical microscope, and electron backscatter diffractometer (EBSD), combined with digital image correlation (DIC) analysis method, the damage evolution behavior of copper‐containing antibacterial stainless steel in large deformation area and small deformation area under different loading rates is investigated. The results show that with the increase of the loading rate, the temperature rise induces local adiabatic shear bands in the microstructure, increasing work hardening, and a decrease in ultimate stress and full elongation. The damage evolves in the large deformation area, the sample is mainly deformed rapidly, the grain deformation degree is large, and the deformation basically stops in the small deformation area. The damage factor of the specimens in the large deformation zone and the small deformation zone increases with the increase of strain, and the damage deformation rate and the critical damage factor decrease with the increase of the loading rate. Based on the DIC method, the damage evolution equations of copper‐containing antibacterial stainless steel samples in large and small deformation regions under different loading rates are established, which effectively reflect the damage evolution laws at different loading rates.

Bond Behavior of Deformed Bars in Self-Compacting Lightweight Aggregate Concrete Subjected to Lateral Tensions

The bond performance of reinforcing bars to concrete, an indispensable factor in designing reinforced concrete structures, is deeply influenced by the stress states of surrounding concrete. In recent decades, although self-compacting lightweight aggregate concrete (SCLC) has gained popularity in architectural engineering, the bond stress-slip relationship of deformed bars in SCLC under lateral tension remains unknown. In this study, 179 pullout tests were performed to examine the local bond stress-slip behavior of deformed bars in SCLC. In addition, the effects of various parameters on the ultimate bond strength and the slip at the ultimate bond stress, as well as the residual bond strength, were analyzed quantitatively. The results showed that both the bond strength and slip at the ultimate stress decrease with the increase of lateral tension regardless of whether it is in pull-out or splitting failure mode. In addition, an empirical formula was proposed that gives a reasonable prediction of the measured bond stress-slip curve of the SCLC.

Influence of Defects and Crystallographic Orientation on Mechanical Behavior of Nanocrystalline Aluminium**Supported by the National Science Foundation of China under Grant No. 11572259

Simulation of molecular dynamics using Embedded Atom Method (EAM) potentials is performed to investigate the mechanical properties of single crystal Al along various crystallographic orientations under tensile loading. The specimens are provided with one or two embedded circular voids to analyze the damage evolution by void growth and coalescence. The simulation result shows that the Young's modulus, yielding stress and ultimate stress decrease with the emergence of the voids. Besides, the simulations show that the single-crystal Al in different crystallographic orientations behaves differently in elongation deformations. The single-crystal Al with 〈100〉 crystallographic orientations has greater ductility than other orientated specimens. The incipient plastic deformation and the stress-strain curves are presented and discussed for further understanding of the mechanical properties of single-crystal Al.

Sirolimus and tacrolimus rather than cyclosporine A cause bone loss in healthy adult male rats

The aim of this work was to study the effects of cyclosporine (CsA), tacrolimus (FK-506), and rapamycin (RAPA) on bone mass, femoral microstructure, femoral biomechanical properties, and bone remodeling in healthy adult male rats.Forty-eight 5-month-old male Wistar rats were used. CsA (2mg/kg/day), FK-506 (3mg/kg/day), RAPA (1.25mg/kg/day), or water (0.5ml/rat/day, control group) were administered orally for 3months.After sacrifice, mean values of immunosuppressants in blood were: CsA (670.4ng/ml), FK-506 (19.2ng/ml), and RAPA (4.8ng/ml). Levels of biochemical parameters were normal in all groups. Femoral BMD was decreased in FK-506 and RAPA groups and lumbar BMD in FK-506 group. Trabecular volume fraction (BV/TV) decreased only in FK-506 group. RAPA and CsA affected femoral cortical structure, but FK-506 did not. FK-506 produced an increase in bone remodeling, and CsA a decrease. FK-506 group showed a decrease in biomechanical parameters relative to all groups. RAPA group showed a decrease in ultimate stress vs control group, and CsA group presented an increase in biomechanical parameters versus control group.We found that administration of both RAPA and FK-506 as monotherapy for healthy rats produced osteopenia. CsA treatment only produces slight damages in the cortical zone of the femur.

The effect of gamma irradiation on the anisotropy of bovine cortical bone

Bone is an anisotropic non-homogenous composite material composed of inorganic bone mineral embedded in an organic matrix. The mechanical behaviour of bone is governed by the volume fraction of these constituents, their mechanical properties, the degree of crystallite-collagen orientation and the bonding between phases. This study aims to evaluate the mechanical role of these constituents in the expression of anisotropy by using gamma irradiation to alter the mineralised collagen fibrils. Bovine cortical cubes were prepared, treated and mechanically tested in uniaxial compression in the axial, radial and tangential orientations. Ultimate stress, ultimate strain, energy to failure and stiffness were evaluated. This study confirmed deleterious effect of gamma irradiation on the axial compressive properties of cortical bone with a dose dependent decrease in ultimate stress of 6% (P=0.231) and 16% (P=0.001) at 15 and 25kGy respectively. This corresponded to a 39% (P=0.058) and 30% (P=0.167) reduction in energy to failure. In the radial orientation there was also a dose dependant decrease in ultimate stress which was consistent with a statistically significant decline in ultimate strain (31% (P=0.003) and 36% (P=0.000)) and energy to failure (36% (P=0.053) and 45% (P=0.008)) at both doses. In the tangential orientation there was a significant 22% (P=0.01) and 23% (P=0.02) decrease in stiffness; though these changes did not alter ultimate stress considerably. This study provides valuable insights into the role of collagen in the radial and tangential orientation when loaded in compression; while also building on the body of work related to the use of gamma irradiation for load bearing bone allografts.

Hydrolytic degradation of polyisobutylene and poly-L -lactide-based multiblock copolymers

The hydrolytic degradation of a series of poly-L-lactide (PLLA)-polyisobutylene (PIB) multiblock copolymers was studied in phosphate buffer solution (pH = 7.4) at 37 °C. The multiblock copolymers were synthesized by chain extension of PLLA-b-PIB-b-PLLA triblock copolymers, which were obtained by ring-opening polymerization of L-lactide initiated by hydroxyallyl telechelic PIB. The degradation strongly depended on the PLLA segment length. At constant PIB segment length, the multiblock copolymer with the shortest PLLA segment length (DPn = 10), showed significant weight loss after 8 weeks, whereas weight loss for DPn = 36 was only observed after 24 weeks. The gel-permeation chromatographic analysis showed a similar decrease in the number-average molecular weight (M n ) with time further supporting the weight loss data. Dynamic mechanical analysis showed a decrease in ultimate stress and modulus with time. The crystallinity of multiblock copolymers changed significantly with degradation time as indicated from differential scanning calorimetric analysis.

Effects of Distal Radius Bone Graft Harvest on the Axial Compressive Strength of the Radius

The effect of metaphyseal cancellous bone graft harvest on distal radius compressive strength is unknown. The purpose of this study was to analyze, in a cadaveric model, changes in distal radius axial compressive strength after distal radius metaphyseal cancellous bone graft harvest. We randomized 15 matched pairs of cadaveric radiuses into 2 groups. In group I, a target harvest of 25% of the total metaphyseal cancellous bone volume was attempted through a standardized oval cortical window. In group II, a target of 50% harvest was attempted. The study specimens and their matched controls from the contralateral side were loaded to failure in axial compression. The amount of bone graft harvested was calculated. The resulting ultimate loads to failure were measured, then expressed as ultimate stress (millipascals--MPa). We analyzed data for the 2 groups and the matched controls using paired Student's t-tests. A smaller amount of bone was harvested than anticipated in both groups. The final average distal radius bone graft harvest for group I was 10%, and for group II, 22.5%. Group I had no statistically significant difference in ultimate stress compared with the contralateral specimens that acted as matched controls (p = .273). Group II had a statistically significant decrease in ultimate stress values compared with matched controls (p = .002). The ultimate stress of group I averaged 92.67% of its matched control, whereas the ultimate stress of group II was 74.8% of its matched control (p = .027). A significant decrease in distal radius ultimate stress occurs when approximately 23% of the metaphyseal cancellous bone is removed through a standardized oval cortical window. When the distal radius is chosen as the bone graft harvest site, we recommend harvest of less than 25% of the total available distal radius metaphyseal cancellous bone to prevent alteration of the load characteristics of the bone.

Flexor Tendon Tissue Engineering: Acellularized and Reseeded Tendon Constructs

Tissue engineering of flexor tendons requires scaffolds with adequate strength and biocompatibility. The biomechanical properties of acellularized and reseeded flexor tendon scaffolds are unknown. Acellularized tendons and reseeded constructs were tested to determine whether the treatment process had altered their biomechanical properties. Rabbit flexor tendons were acellularized using a freeze-thaw cycle followed by trypsin and Triton-X treatment. Complete acellularization of the tendon samples was confirmed by histology and by attempting to obtain viable cells by trypsin treatment of acellularized tendon. Reseeded constructs were obtained by incubating acellularized tendons in a tenocyte suspension. Tensile testing was performed to compare the ultimate tensile stress and elastic modulus of acellularized tendons and reseeded flexor tendon constructs to control flexor tendons. The treatment protocol successfully acellularized flexor tendons. No cells were seen within the tendon on histologic assessment, and no viable cells could be obtained from acellularized tendon. Acellularized tendon was successfully reseeded with tenocytes, although cell adhesion was limited to the surface of the tendon scaffold. Tensile testing showed that acellularized tendon had the same ultimate stress and elastic modulus as normal tendons. Reseeded tendons had the same elastic modulus as normal tendons, but hind-paw tendon constructs showed a decrease in ultimate stress compared with normal tendons (50.09 MPa versus 66.01 MPa, p = 0.026). Acellularized flexor tendons are a potential high-strength scaffold for flexor tendon tissue engineering. This approach of acellularization and reseeding of flexor tendons may provide additional intrasynovial graft material for hand reconstruction.

Mechanical behaviour of polypropylene pipes after the multiple-pass flow-forming process

Flow-forming, which is known also as tube spinning or shear forming, is a cold forming, rotary-point extrusion process. Recent research publications on polypropylene have shown that the mechanical properties: yield strength, tensile strength, tensile modulus and sustainable hoop stress; are improved with increasing percentage of thickness reduction. The present research investigates the possibility to further upgrade the properties of the material by multiple-pass flow-forming instead of single-pass flow-forming. In the investigation, polypropylene pipes were flow-formed in a single pass, two passes, three passes or four passes on a conventional lathe using a twin-rollers system. To evaluate the mechanical properties of the material, the specimens were subjected to the hydrostatic pressure test, and to hardness and tensile tests. The hydrostatic pressure test shows that both hardness and hoop-stress data increase with the number of passes of flow-forming. Observation on the pipe rupture reveals that there are a few macroscopic layers radially across the pipe wall and the rupture gradually transforms from a ductile to brittle nature when the number of passes increases, which suggests that the internal and external surfaces of the polypropylene are more compressive and anisotropic when compared with the interior of the material. The tensile yield behaviour of the material was studied using a Shimadzu Universal Testing Machine. It was found that generally the yield stress and ultimate stress decrease with the number of passes of flow-forming. A reasonable explanation is that when the number of passes increases, the external pipe surface which was flow-formed, and so anisotropic, will offer greater resistance to successive flow-forming passes. This renders even greater non-uniformity in the material texture in that the outer layers are becoming more orientated, hence the yielding process occurs inhomogeneously and the material fails prematurely. Another factor that causes deterioration in the material property is chain polymer scission.