Narrow Results

Shape memory alloys are well known to be used as a ring element for connect coupling two pipes in various fields. In the case of structural and functional designs for a coupling ring of shape memory alloy, we have considered the shape memory effects in multi-axial stress and strain using volumetric strain in each element, so as to make FEM analysis more effective for optimizing the shape and the amount of pre-deformation. Using some uni-axial fundamental test results, as property parameters for FEM, the modeling method simulating the deformation behavior of a coupling ring has been eveloped in order to optimize the configuration and size of a coupling ring. The validity of this FEM modeling method was confirmed by verification experiments.

Nowadays, Severe Plastic Deformation (SPD) methods are at the focus of material researchers and among these methods, Twist Extrusion (TE) is one of promising ones to pave the way of commercialization. In this Investigation the magnitude of strain distribution along 4 selected paths of sample after 3 passes of Twist Extrusion were investigated by computer simulation and its influence on aluminum 1100 microstructure by experimental tests. ABAQUS 6.5 software based on FEM was applied for the former and 70 mm length samples with cross-section of 18*28 mm were exploited for the latter. According to the simulation results, corner, middle of small side, middle of long side and center of the cross-section are placed from maximum to minimum magnitude of strain respectively. Theses achievements were verified with metallographic images in aspect of metal flow and grain size as well.

Surface energies of strained Cu surfaces were studied systematically using first-principles methods. Results showed that the strain-stabilization of Cu surface was anisotropic and strongly related to the strain distribution. This strain-induced approach could be used as an effective way to engineer the surface energies of metals.

In this paper, the biomechanical effectiveness of prophylactic augmentation in preventing fracture was investigated. In vitro biomechanical tests were performed to assess which factors make prophylactic augmentation effective/ineffective in reducing fracture risk. Nondestructive and destructive in vitro tests were performed on isolated osteoporotic vertebrae. Five sets of three-adjacent-vertebrae were tested. The central vertebra of each triplet was tested in the natural condition (control) non-destructively (axial-compression, torsion) and destructively (axial-compression). The two adjacent vertebrae were first tested nondestructively (axial-compression, torsion) pre-augmentation; prophylactic augmentation (uni- or bi-pedicular access) was then performed delivering 5.04mL to 8.44mL of acrylic cement by means of a customized device; quality of augmentation was CT-assessed; the augmented vertebrae were re-tested nondestructively (axial-compression, torsion), and eventually loaded to failure (axial-compression). Vertebral stiffness was correlated with the first-failure, but not with ultimate failure. The force and work to ultimate failure in prophylactic-augmented vertebrae was consistently larger than in the controls. However, in some cases the first-failure force and work in the augmented vertebrae were lower than for the controls. To investigate the reasons for such unpredictable results, the correlation with augmentation quality was analyzed. Some augmentation parameters seemed more correlated with mechanical outcome (statistically not-significant due to the limited sample size): uni-pedicular access resulted in a single cement mass, which tended to increase the force and work to first- and ultimate failure. The specimens with the highest strength and toughness also had: at least 25% cement filling, cement mass shifted anteriorly, and cement-endplate contact. These findings seem to confirm that prophylactic augmentation may aid reducing the risk of fracture. However, inadequate augmentation may have detrimental consequences. This study suggests that, to improve the strength of the augmented vertebrae, more attention should be dedicated to the quality of augmentation in terms of amount and position of the injected cement.

In this paper, a digital image correlation (DIC) method is developed and applied on film cooling holes in the submillimeter scale in high temperature. Compared with the traditional DIC method, the speckle patterning method and the optical system are improved. In detail, a kind of high temperature-resistant black paint is selected as the basecoat, and the white ZrO₂ particles are evenly distributed on the specimen using high-pressure splashing method. Besides, to eliminate the radiation effect of the high-temperature specimen, the blue light source is used to illuminate the specimen, and the optical bandpass filter is placed in front of the camera to allow the blue light passing. In order to verify the DIC method, the strain measurement on a specimen with single skew hole is performed. The relative error in high temperature of the maximum strain between the measurement results and the numerical simulation results given by the finite element method (FEM) is 12%. The strain concentration factor of the single skew hole is measured as 1.83. Finally, the developed method is applied to the strain measurement of the structure with multiple film cooling holes in 870^°C. The X-shape strain distribution can be observed at the hole with maximum stress, which suggests that the strain field of multiple holes has coupling effect. In addition, the strain concentration factor of multiple film cooling holes increases to 2.34.