Unidirectional titanium fiber-reinforced porous titanium with mechanical properties suitable for load-bearing biomaterials.

Biomaterials for load-bearing implants are expected to exhibit mechanical biocompatibility of low stiffness and high strength for avoiding stress shielding and failure of the implants in vivo, respectively. This study aimed to develop porous titanium (Ti) reinforced with long Ti fibers so that the porous Ti exhibited low Young's modulus and high tensile strength. The unidirectional Ti fiber-reinforced porous Ti with porosities (p) of 40%-58% and volume percentages of Ti fiber (Vf) of 3%-33% has been successfully fabricated via the space holder technique. Mechanical testing revealed that its strength was improved, compared with uniform porous Ti because Ti fibers prevent microscopic damage progress. The porous Ti with p = 40% and Vf = 33% exhibited the strength of 233 MPa and Young's modulus of 26 GPa, which were higher than and comparable to those of natural bones, respectively. Hence, the Ti fiber-reinforced porous Ti exhibited ideal mechanical properties for implant applications.

Influence of Strain Gradient on Fatigue Life of Carbon Steel for Pressure Vessels in Low-Cycle and High-Cycle Fatigue Regimes.

This paper discusses how the strain gradient influences the fatigue life of carbon steel in the low-cycle and high-cycle fatigue regimes. To obtain fatigue data under different strain distributions, cyclic alternating bending tests using specimens with different thicknesses and cyclic tension-compression tests were conducted on carbon steel for pressure vessels (SPV235). The crack initiation life and total failure life were evaluated via the strain-based approach. The experimental results showed that the crack initiation life became short with decreasing strain gradient from 102 to 106 cycles in fatigue life. On the other hand, the influence of the strain gradient on the total failure life was different from that on the crack initiation life: although the total failure life of the specimen subjected to cyclic tension-compression was also the shortest, the strain gradient did not affect the total failure life of the specimen subjected to cyclic bending from 102 to 106 cycles in fatigue life. This was because the crack propagation life became longer in a thicker specimen. Hence, these experimental results implied that the fatigue crack initiation life could be characterized by not only strain but also the strain gradient in the low-cycle and high-cycle fatigue regimes.

Mechanical Characterization on Solvent Treated Cellulose Nanofiber Preforms Using Solution Dipping-Hot Press Technique.

Nanocomposites films were prepared by impregnating the solvent treated cellulose nanofiber (SCNF) preforms with epoxy resin using a solution dipping-hot press technique. We investigated the effect of SCNF preforms porosity on the amount of impregnated resin and tensile properties of the corresponding nanocomposites films. The porosity of the CNF preforms was successfully controlled using the solvent exchange with varying CNF concentration. The impregnated resin amount increased as the SCNF preforms porosity increased, respectively. Resulting nanocomposite films showed higher mechanical properties than that of the SCNF preforms. The best mechanical properties of composites were found with the combination of 1 wt % SCNF preform and low viscosity epoxy, exhibiting tensile strength and Young's modulus of 77 MPa and 4.8 GPa, respectively. The composite also showed high fiber volume fraction of more than 60%.

Crystallographic Evaluation of Susceptibility to Intergranular Corrosion in Austenitic Stainless Steel with Various Degrees of Sensitization.

This study investigated the susceptibility to intergranular corrosion (IGC) in austenitic stainless steel with various degrees of sensitization (DOSs) from a microstructural viewpoint based on the coincidence site lattice (CSL) model. IGC testing was conducted using oxalic acid and type 304 stainless steel specimens with electrochemical potentiokinetic reactivation (EPR) ratios that varied from 3 to 30%. As a measure of IGC susceptibility, the width of the corroded groove was used. The relationship between IGC susceptibility, grain boundaries (GB) structure, and EPR ratio of the specimens was evaluated. As a result, the IGC susceptibility cannot be characterized using the  value, irrespective of the DOS of the specimen. The IGC susceptibility increases with increasing unit cell area of CSL boundaries, which is a measure of the stability of the CSL boundaries, and then levels off. The relationship between the IGC susceptibility and unit cell area is sigmoidal, irrespective of the DOS of the specimen. The sigmoid curve shifts rightward and the upper bound of IGC susceptibility decreases with decreasing DOS of the specimen.

Fabrication of alumina-PSZ composites via spark plasma sintering and their mechanical properties.

Alumina-partially stabilized zirconia (PSZ) composites were fabricated via spark plasma sintering (SPS) technique to produce biocompatible materials with superior mechanical properties. The volume fraction of the composites covered from 100% alumina to 100% PSZ. Their sintering state was examined by optical microscopy, density measurement, and X-ray diffraction, and dense composites without any reaction phases could be fabricated, irrespective of PSZ content. Then, three-point bending tests and hardness tests were conducted. The hardness and elastic modulus agreed with the predictions based on the Voigt model and the Eshelby's equivalent inclusion model combined with the Mori-Tanaka's mean field concept, respectively. While the bending strength of the composites ranged from that of monolithic alumina to that of monolithic PSZ, the fracture toughness of the composites improved as compared with the monoliths of alumina and PSZ. We concluded that the use of alumina and PSZ was effective to fabricate the composites with high mechanical performances.

Pseudoaneurysm of the Perforating Branch of the Deep Femoral Artery Following Anterior Cruciate Ligament Reconstruction.

The present report describes the first known, case of a pseudoaneurysm of the perforating branch of the deep femoral artery following anterior cruciate ligament (ACL) reconstruction. A 19-year-old man underwent ACL reconstruction using the outside-in femoral tunnel-creation method. Seven days after the surgery, he complained of abnormal thigh pain and had swelling with local heat on the distal lateral thigh. Magnetic resonance imaging, computed tomography, and color Doppler ultrasonography showed the pseudoaneurysm in the thigh. Resection surgery was successfully performed by a vascular surgeon 12 days after ACL reconstruction. Careful examination and awareness of postoperative symptoms such as thigh pain and swelling after ACL reconstruction were critical for the early diagnosis of pseudoaneurysm.

Simulation of water impregnation through vertically aligned CNT forests using a molecular dynamics method.

The flow rate of water through carbon nanotube (CNT) membranes is considerably large. Hence, CNT membranes can be used in nanofluidic applications. In this work, we performed a molecular dynamics (MD) simulation of the introduction of water into CNTs in the CNT membranes, especially in vertically aligned CNT forests. The results showed that the Knudsen number (Kn) increased with an increasing volume fraction of CNT (VC) and was greater than 10(-3) for each VC. Beyond this value, the flow became a slip flow. Further, the permeability increased as VC increased in the actual state calculated by the MD simulation, whereas the permeability in the no-slip state predicted by the Hagen-Poiseuille relationship decreased. Thus, a clear divergence in the permeability trend existed between the states. Finally, the flow enhancement ranged from 0.1 to 23,800, and the results show that water easily permeates as VC increases.