Effective Load Transfer Research Articles

Analysis of Corrective Distal Tibio-Fibular Osteotomy for Medial Compartment Osteoarthritis and Evaluation of Prognostic Factors: Consecutive 67 Cases in One Center

Category: Ankle Arthritis; Ankle; Arthroscopy Introduction/Purpose: A supramalleolar osteotomy is a joint-sparing procedure that can change the mechanical axis load on the ankle joint in the coronal-sagittal planes. Restoration of the axial alignment allows for redistribution of loads to the less affected area of articular cartilage, slowing down or even stopping further articular degeneration. It has been reported that supramalleolar osteotomy has a useful effect in asymmetric varus ankle and medial compartment osteoarthritis, but as far as we know there are not many papers conducted in one center for large cases based study. In our paper, we analyzed the results of multiple cases (67 cases) of supramalleolar osteotomy surgical procedure performed in our center and make insight about prognostic factors like high talar tilt and takakura stage. Methods: From August 2007 to May 2020, a retrospective study was conducted on 67 ankles which underwent distal tibio-fibular osteotomy due to medial compartment osteoarthritis and asymmetric varus ankle in our center. The articular cartilage was evaluated simultaneously with the distal tibio-fibular osteotomy through arthroscopy exam intraoperatively. The mean age was 58.6 years(range 37-73 years). American Orthopaedic Foot & Ankle Society (AOFAS) ankle-hindfoot score, Visual analog scale (Vas) pain score, Range of motion (ROM) and patient satisfaction were used for functional evaluations. Ankle osteoarthritis was classified by Takakura stage, and the tibial anterior surface angle (TAS), tibial lateral surface angle (TLS) and talar tilt angle were measured for radiological evaluations. And, groups were divided according to the Takakura stage, and whether there were significant differences in the measured values was compared. Results: When Preop IIIB and Preop II, IIIA groups were compared, last fu AOFAS score and Pain vas score showed no significant difference. Talar tilt angle showed significant higher value in Preop IIIB group(p<0.05). And TAS angle showed bigger correction in Preop IIIB group with borderline difference. (p=0.07) It seems that overcorrected TAS angle came out to maximize the effect of load transfer to laterally intra-operatively. And it is thought that the overcorrected TAS angle had a good effect on the clinical outcome. When Preop IIIB group were divided stage improved group with not improved group and compared each other, last fu AOFAS score and ROM showed worse results in Postop IIIB group significantly. (p<0.05) Talar tilt showed higher value in Postop IIIB group on preop with borderline differences.(p=0.06) TAS angle showed no significant differences.(p=0.58) Conclusion: We performed SMO for stage IIIB medial ankle OA with significant TAS overcorrection, and achieved favorable clinical outcomes (AOFAS 85.1) when compared with preop stage IIIA group (AOFAS 85.6). Postop stage IIIB group showed higher preop talar tilt angles with poor AOFAS score when compared with postop takakura stage improved group (10.7 and 7.6). Many preop IIIB cases are found to be good candidate for SMO, but skillful selection for SMO is required for good results.

Effect of Ti-6Al-4V particle reinforcements on mechanical properties of Mg-9Al-1Zn alloy

Mg-9Al-1Zn (AZ91) magnesium matrix composites reinforced by Ti-6Al-4V (TC4) particles were successfully prepared via powder metallurgical method. The yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) showed a mountain-like tendency with the increase of the TC4 content. The mechanical properties of AZ91 magnesium matrix composites reached the optimal point with TC4 content of 10 wt.%, realizing YS, UTS, and EL of 335 MPa, 370 MPa, and 6.4%, respectively. The improvement of mechanical properties can be attributed to the effective load transfer from the magnesium matrix to the TC4 particles, dislocations associated with the difference in the coefficient of thermal expansion, good interfacial bonding between the Mg matrix and TC4 particles, and grain refinement strengthening.

Mechanical Behaviour and Morphology of Thixoformed Aluminium Alloy Reinforced by Graphene.

Thixoforming is a promising method that offers several advantages over both liquid and solid processing. This process utilizes semi-solid behaviour and reduces macrosegregation, porosity and forming forces during the shaping process. Microstructural and mechanical characterization of 0.3, 0.5 and 1.0 wt% graphene nanoplatelet (GNP) reinforced A356 aluminium alloy composite fabricated by thixoforming was investigated. Stir casting was employed to fabricate feedstocks before they were thixoformed at 50% liquid. The microstructure was characterized and evaluated by field emission scanning electron microscopy with an energy dispersive X-ray detector and X-ray diffraction. Mechanical testing, such as microhardness and tensile testing, was also performed to estimate the mechanical properties of the composites. The incorporation of 0.3 wt.% GNPs in Al alloy increased by about 27% in ultimate tensile strength and 29% in hardness. The enhancement in tensile strength is primarily attributed to load transfer strengthening due to the uniform dispersion of these GNPs within the Al matrix, which promotes effective load transfer during tensile deformation, and GNPs’ wrinkled surface structure. Simultaneously, the addition of GNPs enhances the grain refinement effect of the Al alloy matrix, resulting in a grain size strengthening mechanism of the GNPs/Al composites. The results reveal that thixoformed composite microstructure consists of uniformly distributed GNPs, α-Al globules and fine fibrous Si particles. The composites’ grains were refined and equiaxed, and the mechanical properties were improved significantly. This study creates a new method for incorporating GNPs into Al alloy for high-performance composites.

Microstructure and mechanical properties of in-situ nitride-reinforced refractory high-entropy alloy TiZrHfNbTa matrix composites

Refractory high entropy alloy TiZrHfNbTa matrix composites reinforced with in-situ nitrides were prepared by vacuum arc melting. The designed composites are composed of BCC matrix and FCC nitride phases, with a particular orientation relationship between them: 111BCC∥011MN,101̅BCC∥200MN,11̅0BCC∥11̅1MN. The composites show enhanced strengths both at room temperature and high temperature compared with the matrix alloy and increase with the increment of N content. The ambient and elevated temperature (1000 ℃) compressive yield strength is up to 2125 MPa and 350 MPa, respectively, and decent fracture strains (>19.3%) at room temperature are maintained. The underlying strengthening mechanisms are discussed systematically, and the increase in strength is mainly attributed to the combination of dislocation strengthening, load-transfer effect and Orowan strengthening.

Lessons from residential electricity demand analysis on the time of use pricing experiment in South Korea

This study analyzes a large-scale Time of Use (TOU) pricing experiment, the first attempt in South Korea, where a single standard rate under increasing block pricing is applied to all residential customers. The experiment was conducted for 2033 households living in 16 apartment complexes, where the control group was subject to the current standard rate, while the two treatment groups had different rate schedules under TOU pricing. Using the data that included both the pre-experimental period (September 2018–September 2019) and post-experimental period (October 2019–August 2020), we built on a two-level electricity demand model to analyze (1) if TOU pricing effectively transfers the peak demand of residential customers within a day, and (2) the changes in daily electricity consumption. We found that the households effectively reduced the peak demand in response to relatively high prices. However, unlike the control group, whose price responsiveness did not change over the sample period, that of the treatment groups decreased in the post-experimental period, thus resulting in increased intermediate consumption. The reason is the reduced price index resulted from the effective load transfer of households, combined with low intermediate price that does not reduce consumption. The price schedule under TOU pricing should be reexamined for social welfare.

Nano-silver modified carbon nanotubes to reinforce the copper matrix composites and their mechanical properties

• The powder electrodeposition technology is employed to synthesize coating material. • CNT-Ag is uniformly distributed in copper matrix. • Ag improves the wettability of carbon nanotubes with copper matrix. • Ag particles played a “pinning” role of the CNTs and improve the load transfer capacity. In ensuring the effective load transfer of carbon nanotubes (CNTs) reinforced copper (Cu)-based composites, good and stable interface contact is a key factor. Powder electrodeposition technology is used in the present study to coat silver (Ag) nanoparticles on CNTs for the first time. Subsequently, by ball milling and spark plasma sintering, uniform distribution of CNTs in the Cu matrix and tight Cu/C interface bonding are successfully achieved. It is found that Ag nanoparticles with a size of 5 nm are evenly embedded in the surface of CNTs. The results reveal that the agglomeration of CNTs is prevented by the addition of Ag nanoparticles and the adhesion between CNTs and Cu matrix is enhanced by the formation of coherent interface. Further, the load transfer of composite materials is effectively realized by the pinning effect of Ag particles on CNTs. The tensile strength, elongation, and conductivity of the 0.75 CNT-Ag/Cu samples were 314 MPa, 24.8%, and 93.6% IACS, respectively, which are 40.1%, 818%, and 3.3% higher than those of the CNT/Cu samples, respectively. The present method provides a new direction for the uniform coating powder materials and the synergistic strengthening of metal matrix composites.

Biomechanical Comparison between Isobar and Dynamic-Transitional Optima (DTO) Hybrid Lumbar Fixators: A Lumbosacral Finite Element and Intersegmental Motion Analysis.

Biomechanical performance of longitudinal component in dynamic hybrid devices was evaluated to display the load-transfer effects of Dynesys cord spacer or Isobar damper-joint dynamic stabilizer on junctional problem based on various disc degenerations. The dynamic component was adapted at the mildly degenerative L3–L4 segment, and the static component was fixed at the moderately degenerative L4–L5 segment under a displacement-controlled mode for the finite element study. Furthermore, an intersegmental motion behavior was analyzed experimentally on the synthetic model under a load-controlled mode. Isobar or DTO hybrid fixator could reduce stress/motion at transition segment, but compensation was affected at the cephalic adjacent segment more than the caudal one. Within the trade-off region (as a motion-preserving balance between the transition and adjacent segments), the stiffness-related problem was reduced mostly in flexion by a flexible Dynesys cord. In contrast, Isobar damper afforded the effect of maximal allowable displacement (more than peak axial stiffness) to reduce stress within the pedicle and at facet joint. Pedicle-screw travel at transition level was related to the extent of disc degeneration in Isobar damper-joint (more than Dynesys cord spacer) attributing to the design effect of axial displacement and angular rotation under motion. In biomechanical characteristics relevant to clinical use, longitudinal cord/damper of dynamic hybrid lumbar fixators should be designed with less interface stress occurring at the screw-vertebral junction and facet joint to decrease pedicle screw loosening/breakage under various disc degenerations.

Nano-TiB whiskers reinforced Ti–6Al–4 V matrix composite fabricated by direct laser deposition: Microstructure and mechanical properties

Titanium matrix composites (TMCs) have attracted widespread research interest due to their excellent properties. Herein, TMC reinforced with quasi-continuous reticular nano-TiB whiskers (nano-TiBw) was fabricated via a direct laser deposition method. The network of TiB reinforcements was found to be equiaxial and dendritic, and the addition of boron was shown to be beneficial to the equiaxial transition and refinement of α grains. The interface between the nano-TiBw and Ti64 matrix was observed to be clean and flat. The microhardness of the TMC was 465.1 HV0.025, 31% higher than that of the Ti64 alloy. Compressive tests showed that the TMC exhibited high ultimate compressive strength and good plasticity due to the grain refinement of the matrix and load transfer effect of nano-TiBw. The lower friction coefficients, smaller wear tracks, and minor wear weight loss revealed the superior wear resistance of the TMC in comparison to that of the Ti64 alloy. The reticular TiBw was found to be responsible for reducing the sensitivity of the TMC to adhesive wear.

Solidification microstructure, aging evolution and creep resistance of laser powder-bed fused Al-7Ce-8Mg (wt%)

The solidification microstructure and the aging- and creep-resistances of a laser powder-bed fused (LPBF) hypoeutectic Al-7.3Ce-7.7Mg (wt%) alloy were investigated. Optimized process parameters allowed to produce specimens with > 99.7% relative density and high hardness (~1650 MPa), without solidification cracking despite a relatively coarse grain size (~ 30 µm). Two distinct solidification microstructures are observed within the solidified melt pools: (i) eutectic α-Al(Mg) and Al 13 CeMg 6 (a metastable phase) at the bottom pool region, and (ii) eutectic α-Al(Mg) and Al 11 Ce 3 (a stable phase) precipitates at the top pool region. The high hardness is predominantly attributed to Orowan strengthening and load-transfer effects from the Ce-rich precipitates, but solid-solution hardening from Mg is also quite pronounced, as most Mg resides in α-Al. Aging at 325 or 400 °C causes a continuous, slow hardness drop, but 85–90% of the initial hardness is retained after over 1000 h aging, consistent with the observation that the Ce-rich precipitates within the grains show very sluggish coarsening, making the alloy highly resistant to aging. The alloy exhibits two creep regimes at 300 ºC. At stresses below 18–20 MPa, diffusional creep is operating with signs of grain-boundary sliding inhibition due to Ce-rich precipitates at grain boundaries. At higher stresses, dislocation climb with either stress-invariant or stress-dependent subgrain structure is dominant, with additional load-transfer contributions and possibly a threshold stress due to dislocation-precipitate interactions. The alloy also exhibits much lower steady-state strain rates (e.g., two orders of magnitude lower at 20 MPa) as compared to a compositionally-similar, but conventionally-cast Al-Ce-Mg alloy with much coarser microstructure, demonstrating that LPBF Al-7.3Ce-7.7Mg alloy – because of its fine precipitates and despite its fine grain size - is well suited for long-term uses under stress at 300 ºC.

Overturning progressive collapse mechanism and control methods of excavations retained by cantilever piles

Deep excavation accidents occur frequently, including overturning progressive collapse (OPC) caused by local over-excavation or other reasons. However, limited research has been presented on the mechanism, evaluation index and control methods of such progressive failure. Therefore, based on an overturning collapse accident of an excavation retained by double-row piles, this paper uses the finite difference method (FDM) to study the OPC mechanism. The influence of local over-excavation on the internal force, displacement and stability of double-row piles was analyzed. To evaluate the risk of OPC, the anti-overturning stability value (ASV) and modified overturning stability index (MOSI) were proposed as evaluation indexes of overturning displacement and overturning stability. The results show that overturning collapse in the local over-excavation area (LOA) developed to adjacent retaining structures through the loading effect of the soil arch in the active zone, the unloading effect of the soil in the passive zone and the load transfer effect of the capping beam. The ASV can be used to predict the scale of retaining piles that will experience additional displacement caused by local over-excavation. Compared with the traditional overturning stability index (OSI) and the ASV, the MOSI can better reflect the occurrence of OPC and its scale. A capping beam cannot reduce the risk of progressive failure but will increase the risk and degree of OPC, which is different from the progressive bending collapse of cantilever excavations. Therefore, when calculating the overturning stability of retaining structures without considering the load transfer effect of the capping beam, the scale of the OPC outside the LOA will be severely underestimated. Extending the retaining piles and reinforcing the soil in the passive zone in the LOA can control the development of OPC, but the two measures have their own limitations and should be selected according to specific project conditions.

Microstructure evolution and mechanical properties of in-situ ZrB2/Al7085 nanocomposites during hot rolling deformation

In this study, ZrB2/Al7085 nanocomposites were fabricated by in-situ reaction with KBF4 and K2ZrF6 fluoride powders during casting, then hot deformation and heat treatment were applied to the sheet product. The deformation by hot rolling was employed to change the distribution of second phases and ZrB2 nanoparticles and significantly improve the microstructure of the matrix. TEM results indicate the semi-coherent relationship between ZrB2 particle and α-Al on the interface without intermediate products. The contributions of ZrB2 particles on composite are described by refining Al7085 grain size to 47% as heterogeneous nuclei during solidification and accelerating to decrease the residual stress and reduce anisotropy during heat treatment. Meanwhile, Al3Zr precipitate in composites is refined to half size in Al 7085. Compared to the Al7085, mechanical property on composite is enhanced when the ZrB2 volume fraction achieves 1% after quenching with 465 ℃−10 min and artificial aging of 120 ℃−5 h/160–10 h. The strengthening mechanisms are grain refinement, coefficient of thermal expansion, Orowan strengthening, and load transfer effect and corresponding strengthening contributions are 3.6 MPa,7.7 MPa,20 MPa, and 2.7 MPa. Our study shows the roles of ZrB2 particles act on composite in different processing statuses and provides the basic strengthening way caused by ZrB2 nanoparticles. Our study shows the roles of ZrB2 particles act on composite in different processing statuses and provides the basic strengthening way caused by ZrB2 nanoparticles.

Geogrid-soil interaction: experimental analysis of factors influencing load transfer

This paper presents interaction experiments with transparent soil to investigate the load transfer at the interface of different geosynthetic reinforcements. Microscopic interaction performance was evaluated in terms of mobilised tensile loads and interfacial shear stresses resulting from the relative movement between geosynthetic and soil. The effects of geogrid aperture size, tensile stiffness, geogrid type and reinforcement configurations on the load transfer were analysed. It was found that with increasing soil deformation, the contribution of friction to the total load transfer decreased and the transverse ribs were increasingly activated. The interfacial shear stresses were reduced as the ratio of geogrid aperture to mean particle size increased, resulting in lower geogrid loads. Higher geogrid loads were mobilised with increasing tensile stiffness of the reinforcement, but lower displacements of geogrid and adjacent soil occurred. Consistent results were found for woven PET and laid PP geogrids. The most effective load transfer was obtained for the aperture configuration with two closely spaced transverse members at each rib, as the soil particles were additionally confined. When the geogrid was attached to a nonwoven geotextile, the separation function was enabled, but the reinforcement performance of the geocomposite was lower due to reduced particle-aperture interaction.

Experimental Investigation of h-Type Supporting System for Excavation beneath Existing Underground Space

A double-row pile support system combined with existing and additional support piles offers an effective solution for further excavation beneath existing underground space. A large-scale test chamber was therefore built to simulate the whole construction process of underground space extension. Several parallel tests are conducted through observation, data monitoring, and analysis to study the influence of several parameters on an h-type support system containing double-row piles. The relevant parameters include pile row spacing, pile length ratio, pile-head constraint, and in-service foundation pile. The tests reveal that a significant load-transfer effect is generated between the pile rows, and increasing the spacing between pile rows within a certain range can lead to a more reasonable distribution of bending moments and pile force. The displacement of the pile top and its rate of increase are directly proportional to excavation depth, and additional excavation to the bottom of the back-row piles tends to be a critical point, after which the deformation will be significant. The stability of the system varies inversely with the reduction in pile length ratio, but is positively related to the existing pile-head constraint. Furthermore, in-service foundation piles can result in increased bending moments and reduced displacement of the pile top. Finally, the rationality of the model test results was verified according to the numerical simulation and the stability of the double-row piles support system was calculated.

Biomimetic metal–organic framework-derived porous carbon welded carbon nanotube networks for strain sensors with high sensitivity and wide sensing range

Due to the weak interaction between the adjacent individual fillers of sensing materials, the destruction of conductive percolation network under large and cyclic deformations results in a narrow sensing region and unsatisfactory durability. Inspired by the geometries of spider web and spider slit organ, a versatile strain-sensing platform with metal–organic framework-derived porous carbon-welding carbon nanotube (MPC–w–CNT) percolation networks is reported by soldering the crossing-points of CNTs using MPCs followed by embedding in poly(styrene-block-butadiene-block-styrene) (SBS), which can enable effective transfer of electrons and load among adjacent CNTs as well as avoid the interfacial slippage during cyclic processes of stretching-releasing. The junction bonding could enable the bioinspired strain sensors to detect small and large deformations with a low limit of detection (0.0085% strain), a large sensing region (∼640% strain), high sensitivity (∼7378.26), and short response time (∼122.50 ms), along with excellent reliability (∼1,000 stretching-releasing cycles). The superiority of these sensing performances is assigned to the combination of welding design of hierarchical MPC–w–CNT networks and selection of SBS. These excellent sensing performances allow the bioinspired sensors to detect the full range of human movements. The unique junction bonding strategy can be applied in other nanomaterial systems to develop stretchable electronics.

Effect of hybrid carbon nanofillers at percolation on electrical and mechanical properties of glass fiber reinforced epoxy

AbstractMulti walled carbon nanotubes and graphene nanoplatelets are novel fillers possessing exceptional intrinsic characteristics, such as high aspect ratio, strength, and good compatibility. These fillers are integrated into a glass fiber reinforced epoxy using a pultrusion process with a mixing ratio of 2:3 to attain the synergetic effect. The electrical and mechanical properties of the composites containing combinations of multi walled carbon nanotubes (0.4 wt%), graphene nanoplatelets (0.6 wt%) and micron aluminum trihydrate (2 wt%) fillers is studied. Significant improvement in electrical and mechanical properties is achieved. This study reveals that the incorporation of hybrid carbon nanofillers into epoxy leads to improved dielectric constant, AC conductivity and mechanical properties as compared with the base epoxy composite with glass reinforcement. The AC conductivity increases from 10−9 to 10−1 S/m and dielectric constant from 3.6 to 100 due to carbon fillers. The mean tensile strength improves from 433 MPa of the base epoxy composite to 508 MPa in carbon‐filled composite. The compressive strength improves from 630 to 681 MPa due to incorporation of carbon fillers signifying the improvement in load transfer effectiveness. The effect of carbon fillers on the flexural strength and hardness is minimal. The experimental data on mechanical parameters have been validated using theoretical modeling and a good correlation is established.

Comparing evolution of precipitates and strength upon aging of cast and laser-remelted Al–8Ce-0.2Sc-0.1Zr (wt.%)

The microstructural evolutions, upon solidification and subsequent aging, and associated hardening effects for both cast and laser-surface-remelted Al–8Ce-0.2Sc-0.1Zr (wt.%) hypo-eutectic alloy are investigated with focus on precipitation and coarsening behavior of their Al11Ce3 and L12-Al3(Sc,Zr) precipitates. Laser surface remelting, which produces solidification conditions typical of additive manufacturing (AM) processes, suppresses formation of undesirable primary Al11Ce3 and Al3(Sc,Zr) precipitates on solidification. It also greatly refines the interlamellar spacing of the eutectic Al11Ce3 phase, thus enhancing the Orowan strengthening effect as compared to the cast alloy, beyond the load-transfer effect from the Al11Ce3 phase. Subsequent aging at 325 °C leads to further hardening of both alloys due to secondary Al3(Sc,Zr) nanoprecipitation, with much more pronounced hardness increases in the laser-remelted alloy, owing to a higher number density of finer Al3(Sc,Zr) nanoprecipitates, as compared to the cast alloy. This improvement is rationalized by an enhancement of Al3(Sc,Zr) nucleation rate upon aging of laser-remelted alloy, as compared to the cast alloy, considering differences in elemental supersaturation within the α-Al regions of these alloys. Prolonged aging, up to 1000 h, at 325 °C causes the hardness of both alloys to decline relatively slowly, implying that this alloy is suitable for AM processes and subsequent applications where high strength and good heat resistance are needed.

A novel heterogeneous network structure titanium matrix composite with a combination of strength and ductility

Boron (B) and graphene oxide nanoplates (GOs) reinforced Ti6Al4V (Ti64) titanium matrix composite ((B + GOs)/Ti64) with a heterogeneous network structure was prepared via spark plasma sintering (SPS). The results show that the heterogeneous network structure composites consist of fine grain zones with a network structure and coarse grain zones with good ductility. Compared with Ti64 alloy, heterogeneous network structure (B + GOs)/Ti64 composites has higher strength and ductility, both of which are superior to homogeneous network structure (B + GOs)/Ti64composite. The increase in strength is attributed to the grain refinement effect within the fine grain zone and the load transfer effect of the reinforcement at the interface. The ductility is mainly dependent on the existence of large size matrix and the improvement of deformation coordination and cracks propagation by the heterogeneous network structure. Finally, the conflict between the strength and plasticity of the composites is effectively reconciled. This provides a new idea for the design of high-performance titanium matrix composites.

Cavitation-resistant intergranular precipitates enhance creep performance of θ′-strengthened Al-Cu based alloys

Tensile and compressive creep properties of a quaternary Al-Cu-Mn-Zr (ACMZ) alloy and its commercial counterpart (Al-Cu-Mn-Zr with Ni, Co and Sb additions, RR350) are investigated at 300°C. At low stresses up to 30 MPa where diffusional creep dominates, creep resistance is the same in tension and compression and RR350 deforms more slowly than ACMZ, consistent with RR350 alloy's larger linear fraction of intergranular precipitates (Al7Cu2(NiFe) and Al9FeNi for RR350 vs. θ-Al2Cu for ACMZ) and a reduced fraction of precipitate-free zones near grain boundaries. At stresses between 30 and 80 MPa, dislocation creep with a stress exponent n ∼ 3 becomes rate-limiting in compression, which is expected to be controlled by θ′ precipitates within the grain bulk. By contrast, in tension, enhanced creep rate and higher apparent stress exponents are measured, consistent with cavitation at intergranular precipitates becoming increasingly dominant as the stress increases. In the dislocation creep regime, RR350 alloy is again more creep resistant than ACMZ alloy, which is related to three mechanisms (i) a reduced fraction of softer precipitate-free zones, (ii) more effective load transfer to intergranular precipitates, and (iii) reduced cavitation. A model for cavitation is applied to calculate tensile creep rates from compressive creep rates and the model successfully predicts the improved tensile creep resistance of the RR350 alloy. The present investigation underscores the importance of intergranular grain boundary precipitates, in addition to strengthening θ′ precipitates, in enhancing the creep resistance of Al-Cu alloys.

The load transfer effect of monopolar and bipolar radial head prosthesis designs on capitellar cartilage: A comparative biomechanical cadaver study.

The aim of this study was to determine whether bipolar radial head arthroplasty may transfer less load to the capitellum than monopolar radial head arthroplasty and native radial heads. Six human elbow joints were obtained from six fresh frozen cadavers (3 males, 3 females; mean age = 78 years, age range = 66-80). None of the elbow joints had a previous osseous injury, a chondral defect, osteoarthritis, or instability. In group 1, load transfer of the native radial head was measured in each specimen under 100 N of compression force using a custom-made load cell at 0°, 30°, 60°, 90°, and 120° flexion of the elbow in supination, neutral rotation, and pronation, respectively. After excision of the radial heads, the same testing protocol was first applied for monopolar radial head arthroplasty (Group 2) and then for bipolar radial head arthroplasty (Group 3). The mean load transfer on the capitellum was significantly higher in each forearm rotation and all angles of the elbow flexion in the arthroplasty groups than the native radial head group. Mean load transfer values of bipolar prostheses were between the values of native radial heads and monopolar prostheses in all positions. Bipolar prostheses showed similar load transfer characteristics compared to those of the native radial head in supination at 60° flexion; in neutral rotation at 0°, 30°, 60°, and 120° flexion; and in pronation at 90° and 120° flexion. The results of this study have revealed that bipolar radial head arthroplasty transfers similar loading as the native radial head on the capitellum in certain forearm positions and at elbow flexion angles. No significant differences could be found between load transfer values of bipolar head design and monopolar head design except in the pronation at full extension.

Formation of the orientation relationship-dependent interfacial carbide in Al matrix composite affected by architectured carbon nanotube

In-situ formed carbides at interface can enhance the interfacial bonding and load-transfer effect in nanocarbon/Al composites, but always sacrifice the structure integrity of reinforcement, inevitably degrading the strengthening efficiency. To alleviate such limitation, a novel hybrid leaf-like carbon nanotube (CNT)-graphene nanoribbon (GNR), architectured via partially longitudinal unzipping of multi-walled CNT (UZCNT), was adopted to reinforce Al matrix composites. Results show that the prominent mechanical properties of UZCNT/Al over CNT/Al were achieved, which originates from the in-situ formed interfacial Al4C3 together with the well-retained integrity of UZCNT. The regulated interfacial reaction between UZCNT and Al generates dense nano-sized Al4C3 (diameter: 14–19 nm, length: 36–82 nm), rather than its submicron-sized counterpart (diameter: 26–37 nm, length: 111–186 nm) with low number density which forms in unmodified CNT/Al composites. Systematic analysis indicates that the interfacial Al4C3 in UZCNT/Al forms via “nucleation-growth” pattern, contrary to the predominant epitaxial growth of Al4C3 in CNT/Al. It is revealed that UZCNT can stimulate Al4C3 nucleation via reducing the nucleation energy barrier and increasing the number of nucleation sites. Meanwhile, finite active C atoms and low-defective inner walls in UZCNT retard the fast growth of Al4C3 after nucleation. Such “nucleation-growth” pattern renders the formation of high number-density nano-sized Al4C3 at GNR margin in UZCNT/Al. Atomic-scale characterizations demonstrate that the coherent/semi-coherent Al4C3-Al interfaces in UZCNT/Al preferentially exhibit specific orientation relationships, most of which are reproducible by the edge-to-edge matching model. The present work is supposed to provide important insights on interfacial carbide formation in nanocarbon/metal composites.