Dislocation Force Research Articles

Effects of solid solution elements on damping capacities of binary magnesium alloys

Effects of solid solution elements on damping capacities of four Mg-1at%X binary alloys (X = Zn, Sn, Ga, Al) with similar grain sizes are carefully investigated with pure Mg as comparison. The strain-amplitude-independent damping capacity of the solid solution alloy decreases with the higher lattice distortion caused by solute atoms, while the yield strength is just the opposite. The strain-amplitude-dependent damping capacity is affected by the lattice distortion, the stacking fault energy and the mixing enthalpy between solute atoms and Mg atoms, while the stacking fault energy is the dominant. The Mg-1at%Sn alloy exhibits the highest strain-amplitude-independent damping capacity, while the Mg-1at%Al alloy has the best strain-amplitude-dependent damping capacity at room temperature. When the temperature rises to about 100 °C, the Mg-1at%Zn alloy with the largest lattice distortion degree has the best strain-amplitude-independent damping. This may be related to the increase of the dynamic force for dislocation bowing caused by thermal activation.

Hot deformation behavior and flow stress modeling of a Ni-based superalloy

The deformation behavior of a novel Ni-based superalloy was investigated using isothermal compression on a Gleeble system at temperatures between 1050 and 1210 °C with strain rates between 0.001 and 0.1 s−1. Flow-stress curves and electron backscatter diffraction maps were employed to experimentally identify the various flow mechanisms operative during deformation. Deformation at temperatures below 1130 °C presented strong work hardening with limited restoration during dynamic softening leading to partially recrystallized microstructures. Increasing the deformation temperature to and above 1130 °C enhanced the driving force for dislocation and grain boundary mobility thereby enabling dynamic recovery (DRV) and dynamic recrystallization (DRX) mechanisms to better operate. The influence of the strain rate was more evident during deformation at these temperatures. Increasing the strain rate from 0.001 s−1 to 0.1 s−1 resulted in a transition in dominant softening mechanism from DRV to DRX. Flow stress modeling using the Zener-Hollomon parameter was performed to obtain the activation energy and the constitutive equation for hot deformation of the alloy. Strong changes in flow behavior affected the accuracy of the flow stress model, and thus, the model was used alternatively to identify deformation parameters associated with various flow regimes. In doing so, the activation energy and the other equation constants were obtained for each deformation mechanism observed experimentally.

Traction force for peroperative hip dislocation in hip arthroscopy.

Traction force widens the joint space during hip arthroscopy. It is unclear how much the traction force varies and if it is related to the joint space widening. Main goal of our study was to measure the amount of force needed to widen the hip joint. Second goal was to study the relation between this force and the amount of joint space widening. Traction force was measured in 27 patients (of whom 24 female, mean age 41) during arthroscopy. Measurements were performed before the procedure, after vacuum seal release and after capsulotomy. Joint space widening was measured with fluoroscopy and was calibrated. Friedman and Wilcoxon tests were used to measure differences in traction. The Spearman's rho correlation coefficient was used to identify a correlation in traction force and joint space widening. Regression analyses were used to identify relations between age, body mass index (BMI), hip degeneration and traction force. The median traction force before arthroscopy was 714 N, lowered to 520 N after vacuum seal release and to 473 N after capsulotomy (p < 0.001). Median joint space widening was 8.8 mm. Spearmans' rho correlation between traction force and joint space widening was ‒0.13. Median traction force of 714 N resulted in 8.8 mm of joint space widening. This traction force was significantly lowered by 200 N after release of the vacuum seal of the hip and 250 N after additional capsulotomy without loss of joint space narrowing. No significant relation was identified for age, BMI or progression of the Kellgren-Lawrence classification for hip degeneration and traction force. Netherlands Trial Registry number 8610.

Effect of nanotwin and dislocation pileup at twin boundary on dislocation emission from an interfacial collinear crack tip in nanocrystalline bimaterials

The interaction between nanotwin and dislocation pileup at twin boundary and interface cracks are of vital importance in studying the toughening mechanism of nanocrystalline materials. We have developed a theoretical model to discuss the effects of nanotwin and dislocation pileup on dislocation emission from an interfacial collinear crack tip in nanocrystalline bimaterials. The nanotwin as a stress source can be descripted by two disclination dipoles, and some dislocations produced by the grain boundary pile up at twin boundary. Using the complex potential method, the complex form of dislocation force and critical stress intensity factors (SIFs) corresponding to dislocation emission under remote plane loadings are deduced. Through numerical analysis, it is discussed that the effects of twin strength, twin orientation, twin size, twin position, dislocation pileup, crack length, and material constant on the critical SIF corresponding to dislocation emission in detail. The results show that the nanoscale twin and the dislocation pileup at the twin boundary will hinder dislocation emitted from the collinear crack tip and reduce toughness caused by dislocation emission. There is a critical nanotwin size making the critical SIF equal to zero and a best twin position minimizing the value of the critical SIF making dislocations emission easiest. The shear modulus of the two half plane have great influence on the critical SIF.

Effect of the humeral neck-shaft angle and glenosphere lateralization on stability of reverse shoulder arthroplasty: a cadaveric study

Lateralizing the glenosphere and decreasing the humeral neck-shaft angles are implant design parameters that reduce the risk of scapular impingement. The effects of these parameters on joint stability remain unclear. This study evaluated the effect of glenosphere lateralization and humeral neck-shaft angle on joint stability by quantifying the anterior dislocation force in different arm positions. Reverse shoulder arthroplasty was performed on 19 human shoulder specimens. Anterior dislocation force and maximum external rotation were evaluated using a robot-based shoulder simulator. By varying the neck-shaft angle and magnitudes of glenosphere lateralization, 12 configurations were analyzed with the glenohumeral joint in 30° and 60° of abduction, in neutral, and in 30° of external rotation. At 30° of abduction, measurements showed significantly higher dislocation forces for the 9-mm and 6-mm lateralized glenosphere than for the 0-mm (P < .0001, P = .007) nonlateralized glenosphere. At 60° of abduction, measurements showed significantly higher dislocation forces for the 9-mm and 6-mm lateralized glenosphere than for the 0-mm (P < .0001, P = .0007) and 3-mm (P = .0003, P = .04) glenosphere. Configurations with a neck-shaft angle of 135° showed significantly higher dislocation forces than configurations with a neck-shaft angle of 145° (P = .02) or 155° (P = .02) at 30° of abduction in 30° of external rotation. Neck-shaft angle and glenosphere lateralization had no influence on maximum external rotation capability. Glenosphere lateralization significantly increased anterior stability of the glenohumeral joint without influencing the range of passive external rotation. The humeral neck-shaft angle only had a minor effect on anterior stability.

Influence of Acetabular Shell Position and Component Design on Hip Dynamic Dislocation

BackgroundDislocation is a major complication following total hip arthroplasty, with risk factors such as surgical technique, implant positioning, and implant design. Literature has suggested the distance the femoral head must travel before dislocation to be a predictive factor of dislocation where smaller travel distance has increased dislocation risk. The purpose of this study was to compare 3 designs (hemispherical, metal-on-metal, and dual mobility [DM]) in terms of the dynamic dislocation distance and force required to dislocate. MethodsThis dynamic dislocation distance model used a material testing system that defined acetabular component inclination (30°, 45°, and 60°), anteversion angles (0°, 15°, and 30°), and pelvic tilt (5° [standing] and 26° [chair rise]). Testing groups included a hemispherical shell with a modular polyethylene liner and 32-mm head, a metal-on-metal hip resurfacing cup design with a 40-mm CoCr head, and a DM design with a 42-mm outside diameter articulating liner and an inner 28-mm articulating head. ResultsThe dynamic dislocation distance of the DM hip was greater than that of the other designs for all inclination, anteversion, and pelvic tilt angles tested with the exception of 60° inclination/0° anteversion. At 26° pelvic tilt, it was observed that dislocation distance increased with greater anteversion and decreased with larger inclination. ConclusionClinical results have shown the DM design may reduce dislocation. These data support those findings and suggest that if instability is a concern preoperatively or intraoperatively, using a DM implant increases the dynamic dislocation distance.

Safety of intrauterine devices in MRI.

ObjectivesThe paucity of safety information on intrauterine devices (IUD) for magnetic resonance imaging (MRI) examinations is clinically relevant. The aim of this study is to evaluate the MRI safety of clinically used IUDs composed of copper/gold and stainless steel at 1.5T and 3.0T.Materials and methodsWe assessed and compared the displacement force, torque effects, presence of imaging artifacts and heating of IUDs composed of copper/gold (western IUDs) and stainless steel (China) on 1.5 and 3.0T MRI systems.ResultsGold/Copper IUDs can show small deflection angles of 7° ± 7° in the worst-case field gradient of 40T/m (equivalent to magnetic force of 0.5 mN), while the stainless steel IUD experienced significant magnetic force and deflection (Force > 7.5 N; deflection angle 90° ± 1°). Manual rotation and suspension method show no torque effects on gold/copper IUDs but high torque effects were observed by manual rotation on the stainless steel IUD. Heating measurements showed a temperature increase (rescaled to a wbSAR of 4 W/kg) of 1.4°C at 1.5T / 3.4°C at 3.0 T (stainless steel IUD), 3.2°C at 1.5 T / 3.8°C at 3 T (copper/gold IUD), 3.3°C at 1.5 T / 4.8°C at 3 T (copper 1), 3.8°C at 1.5 T / 4.8°C at 3 T (copper 2). The visible imaging artifacts of the copper and gold IUDs at 3 T MRI reach a diameter of 4 mm ± 1 mm, while the stainless steel IUD resulted in artifacts measuring 200mm ± 10 mm when using gradient echo pulse sequences.ConclusionsStandard IUDs (copper/gold) can be considered as conditional for MR safety at 1.5 T and 3.0 T, demonstrating at wbSAR up to 4W/kg and a magnetic field gradient of up to 40T/m with minimal imaging artifacts. The stainless steel IUD, however, induces unacceptable artifacts and is potentially harmful to patients during MRI due to high magnetic dislocation forces and torque (MR unsafe).

Effect of nanotwin and dislocation pileup at twin boundary on dislocation emission from a semi-elliptical blunt crack tip in nanocrystalline materials

The effects of the nanotwin and dislocation pileup at the twin boundary on lattice dislocation emission from a surface semi-elliptical blunt crack in deformed nanocrystalline materials (NCMs) are investigated. The nanotwin as a stress source can be described by a wedge disclination quadrupole. Using the complex variable method, complex analytic solution of stress field, the dislocation force and the critical stress intensity factors (SIFs) for the first edge dislocation emission were obtained. Then, through numerical calculation, the influence of twin size, twin orientation, twin position, twin strength and dislocation pileup, the curvature radius of blunt crack tip on the critical stress intensity factors were discussed in detail. The results show that the nanotwin and dislocation pileup has significant influence on the dislocation emission from the blunt crack tip. The presence of nanotwin and dislocation pileup will increase the most probable emission angle, and increase the critical SIFs for dislocation emission, making it harder for the dislocation to emit from the blunt crack tip and thus to decrease the toughness of materials produced by dislocation emission.

Proposal of a New Dynamic Distraction Device to Treat Complex Periarticular Fractures of the Metacarpophalangeal Joint of Long Finger.

Background: Complex periarticular fractures of the metacarpophalangeal joint (MCPJ) are often challenging to treat. Conservative and operative treatments are often burdened with stiffness, loss of function, and poor clinical outcome. These phenomena could be a direct consequence of long period of immobilization. To promote a short time of immobilization and a quick return to daily activities, it is mandatory to stabilize the fracture maintaining the active range of motion (AROM) of the ray. A simple solution is to reduce the fragments by means of dynamic ligamentotaxis. The authors propose a new dynamic distraction device (DDD) for the MCPJ. Methods: The DDD for the MCPJ was made of Kirschner wires bent and connected to counteract dislocation forces and to allow mobilization of the joint. The DDD was tested on a cadaver model under a simulated load in physiological conditions, and also in metacarpal and proximal phalanx (P1) fracture patterns. The effectiveness of the device was evaluated under fluoroscopy. Results: The data showed that DDD is able to achieve fracture reduction through ligamentotaxis and primary fragments stability and to avoid secondary dislocation during AROM of complex periarticular fractures of the MCPJ. Conclusions: The frame could be an alternative option to treat periarticular fractures of the MCPJ. The DDD implant has several advantages: It is time efficient because assembly and application take only few minutes. Furthermore, it is very versatile; indeed, it can be used in all metacarpal and phalanx bones, even in the central rays.

Effect of cooperative grain boundary sliding and migration on dislocation emission from interface collinear crack tip in nanocrystalline bi-materials

The theoretical model of an edge dislocation near interface collinear crack tips in nanocrystalline bi-materials with cooperative grain boundary sliding and migration is formulated. As a typical example, we focus on analyzing the effect of two disclination dipoles produced by cooperative grain boundary sliding and migration on an edge dislocation emitting from a finite interfacial crack tip in nanocrystalline bi-materials. The dislocation force and the critical stress intensity factors for an edge dislocation emitting from an interface collinear crack tip under remote plane loadings are derived by using the complex potential method. And the influences of grain size, disclination strength, migration distance, sliding distance and interface crack length on the critical stress intensity factors are discussed in detail. It can be found that the effect of cooperative grain boundary sliding and migration deformation on the dislocation emission from interface collinear crack tip lies in the crack length, the dislocation emission angle, and the strength of the cooperative deformation itself.

Effect of Blood Exposure on Push-Out Bond Strength of Four Calcium Silicate Based Cements.

Introduction:The purpose of this study was to compare the push-out bond strength of white ProRoot Mineral Trioxide Aggregate (MTA), Biodentine, calcium-enriched mixture (CEM) cement and Endosequence Root Repair Material (ERRM) putty after exposure to blood. Methods and Materials:A total of 96 root dentin slices with a standardized thickness of 1.00±0.05 mm and standardized canal spaces were randomly divided into 4 main experimental groups (n=24) according to the calcium silicate based cement (CSC) used: white ProRoot MTA, CEM Cement, ERRM Putty and Biodentine. Specimens were exposed to whole fresh human blood and then subdivided into two subgroups depending on the exposure time (24 or 72 h). Push-out bond strength was measured using a universal testing machine. Failure modes were examined under a light microscope under ×10 magnification. Data were analyzed using the two-way ANOVA test. Results:Biodentine exhibited the highest values regardless of the exposure time. The lowest push-out strength values were seen in white ProRoot MTA and CEM cement in both post exposure times. After exposure to blood, the push-out bond strength of all materials increased over time. This increase was only statistically significant in white ProRoot MTA and ERRM specimens. The dominant failure mode in all CSCs was the adhesive mode. Conclusion:Biodentine showed the highest values of push-out bond strength and may be better options for situations encountering higher dislocation forces in a short time after cement application.

Once upon a time.... Dual mobility: history.

Since 1962, the low friction arthroplasty developed by Sir John Charnley has given us very good long terms results at more than 40years follow up, but dislocation remains a major complication. The dislocation rate is a permanent risk during the life of the patient and the prosthesis, defined by J. Caton and D. Berry in 2004 as a cumulative risk. History and concept development: The concept of dual mobility was thought up by G. Bousquet, A. Rambert and J. Rieu in the 1970s (1974-1979). The first one in 1979 was called NOVAE and combined two articulations: one large and one smaller by a recruitement phenomenon increasing the jumps distance and so decreasing dislocation forces. In 2003, D. Noyer published the first paper about the «third articulation»: a true metal/PE bearing. Since 1996, twenty years after the first patent, many dual mobility cups have been developed with various fixation ways and various designs. Today with the same principles there are many differences for the «third generation» with excellent results at more than tenyears FU with less than 1% to 2% dislocation rate in primary, revision, recurrent THA dislocation and THA after femoral neck fractures.

Analysis on the effect of phase boundary in meso-cutting of AISI1045 based on the microstructure-level simulation

In this paper, in order to discover the mechanism of chip formation in meso-cutting, an equivalent homogenous material (EHM) model and a microstructure-level model based on the real microstructure were built up for finite element analysis (FEA) of the meso-cutting process of hot-rolled AISI1045. The advantage of the microstructure-level model over the EHM ones includes its capability in revealing the hidden phenomena and mechanisms related to grain, grain boundary, and phase structure besides the higher prediction precision. And these phenomena and mechanisms are very important for the correct understanding of meso- and micro-cutting. After experimental verification, the microstructure-level model was used to analyze the effects of phase boundary on the chip morphology, strain, stress, etc. in the meso-cutting. It was found that large strain took place in the interior of the ferrite and built up the plumps on the free chip surface. And large strain gradient formed around the phase boundaries by the combining effects of the generation of geometrically necessary dislocations for meeting the deformation compatibility between grains, image force, and pile-up of dislocations. In addition, the reversal of the strain, stress, and strain rate across the phase boundary was noticed as well. At last, the size effect was analyzed from the perspective of the strengthening of material due to the variation of the hydrostatic pressure with the ratio (λ) of ap/re and its effect on defects along the phase boundaries and shear stress.

Anterior stability of the reverse shoulder arthroplasty depending on implant configuration and rotator cuff condition.

The aim of this study was to investigate the stabilizing influence of the rotator cuff as well as the importance of glenosphere and onlay configuration on the anterior stability of the reverse total shoulder replacement (RTSR). A reverse total shoulder replacement was implanted into eight human cadaveric shoulders, and biomechanical testing was performed under three conditions: after implantation of the RTSR, after additional dissection of the subscapularis tendon, and after additional dissection of the infraspinatus and teres minor tendon. Testing was performed in 30° of abduction and three rotational positions: 30° internal rotation, neutral rotation, and 30° external rotation. Furthermore, the 38-mm and 42-mm glenospheres were tested in combination with a standard and a high-mobility humeral onlay. A gradually increased force was applied to the glenohumeral joint in anterior direction until the RTSR dislocated. The 42-mm glenosphere showed superior stability compared with the 38-mm glenosphere. The standard humeral onlay required significantly higher anterior dislocation forces than the more shallow high-mobility onlay. External rotation was the most stable position. Furthermore, isolated detachment of the subscapularis and combined dissection of the infraspinatus, teres minor, and subscapularis tendon increased anterior instability. This study showed superior stability with the 42-mm glenosphere and the more conforming standard onlay. External rotation was the most stable position. Detachment of the subscapularis as well as dissection of the complete rotator cuff decreased anterior stability.

Biomechanical Evaluation of Glenoid Version and Dislocation Direction on the Influence of Anterior Shoulder Instability and Development of Hill-Sachs Lesions

Background: Abnormal glenoid version is a risk factor for shoulder instability. However, the degree to which the variance in version (both anteversion and retroversion) affects one’s predisposition for instability is not well understood. Purpose: To determine the influence of glenoid version on anterior shoulder joint stability and to determine if the direction of the humeral head dislocation is a stimulus for the development of Hill-Sachs lesions. Study Design: Controlled laboratory study. Methods: Ten human cadaveric shoulders (mean age, 59.4 ± 4.3 years) were tested using a custom shoulder dislocation device placed in a position of apprehension (90° of abduction with 90° of external rotation). Glenoid version was adjusted in 5° increments for a total of 6 version angles tested: +10°, +5°, 0°, −5°, −10°, and −15° (anteversion angles are positive, and retroversion angles are negative). Two humeral dislocation directions were tested. The first direction was true anterior through the anterior-posterior glenoid axis. The second dislocation direction was 35° inferior from the anterior-posterior glenoid axis based on the deforming force role of the pectoralis major. The force and energy to dislocate were recorded. Results: Changes in glenoid version manifested a linear effect on the dislocation force. The energy to dislocate increased as a second-order polynomial as a function of increasing glenoid retroversion. Glenoid version of +10° anteversion and −15° retroversion was highly unstable, resulting in spontaneous dislocation in one-quarter (10/40) and one-half (25/40) of the specimens anteriorly and posteriorly, respectively, in the absence of an applied dislocation force. The greater tuberosity was observed to engage with the anterior glenoid rim, consistent with Hill-Sachs lesions, 40% more frequently when the dislocation direction was true anterior compared with 35° inferior from the anterior-posterior glenoid axis. The engagement of the greater tuberosity caused an increase in the energy required to dislocate. Conclusion: Glenoid version has a direct effect on the force required for a dislocation. An anterior-inferior dislocation direction requires less energy for a dislocation and results in a lower risk of the development of a Hill-Sachs lesion than a direct anterior dislocation direction. Clinical Relevance: Consideration should be given to glenoid version when choosing a surgical treatment option for anterior shoulder instability.

Interaction between a screw dislocation and a bridged crack with surface elasticity

We examine the contribution of crack bridging and surface elasticity to the elastic interaction between a mode III finite crack and a screw dislocation. The surface effect on the crack faces is incorporated by using the continuum-based surface/interface model of Gurtin and Murdoch. The crack faces are subjected to a bridging force which is assumed to be proportional to the crack opening displacement, whereas the bridging stiffness is allowed to vary arbitrarily along the crack. By considering a continuous distribution of both screw dislocations and line forces on the crack, the boundary value problem is reduced to two decoupled first-order Cauchy singular integro-differential equations. After the expansion of the unknown line dislocation and line force densities and the known variable bridging stiffness into Chebyshev polynomials, these singular integro-differential equations are solved numerically using the collocation method. Owing to the incorporation of surface elasticity, the stresses at the crack tips only exhibit the weak logarithmic singularity when the dislocation is located on the real axis where the crack is located, whereas in the case when the dislocation is not on the real axis, the stresses at the crack tips exhibit both the weak logarithmic and the strong square-root singularities. The two densities, the crack opening displacement across the crack faces and the image force acting on the screw dislocation are specifically calculated. We note that crack bridging only exerts an effect on the line dislocation density but has no influence on the line force density. In addition, we demonstrate that both surface elasticity and crack bridging can reduce the strengths of the logarithmic stress singularity at the crack tips and the magnitude of the crack opening displacement across the crack faces. Our results also clearly show that both crack bridging and surface elasticity exert a significant influence on the magnitude and direction of the image force acting on the screw dislocation.

Novel device, a temporary guidewire fixator.

A novel device for distal fixation of a guidewire was tested in regards to deployment and retrieval, deposition in the blood stream and force of fixation in a pig model. Eleven pigs were subjected to full anaesthesia and heparinized to active clotting time 250–350 s. Uninterrupted blood flow during 4 h deposition was assessed by angiography and inspected for thrombus deposition upon retrieval. The force of fixation was investigated up to the level of loss of fixation (displacement force). The device was successfully deployed and retrieved in over 40 cases. In one case, an alternative method for bailout retrieval was used. Deposition for 4 h was performed, and uninterrupted blood flow was verified by angiography. No instances of arterial occlusion or thrombosis were detected. The median dislocation force was 7.6 N. No arterial rupture or dissection was detected following the loss of fixation. As a conclusion, the device was considered safe and functional in this animal test model.

Effect of special rotational deformation on dislocation emission from interface collinear crack tip in nanocrystalline bi-materials

The work is devoted to investigate the interaction between the special rotational deformation and interface collinear cracks in nanocrystalline bi-materials. As an illustrative example, the effect of the disclination quadrupole produced by the special rotational deformation on the emission of lattice dislocation from a finite interfacial crack tip in nanocrystalline bi-material is explored theoretically using the complex variable method. The complex form expression of dislocation force and the critical stress intensity factors for the first edge dislocation emission under remote mode I loadings and mode II loadings are deduced. And the influences of material properties, grain size, disclination strength, disclination location and orientation, special rotational deformation orientations, and crack length on the critical stress intensity factors are discussed in detail. The results show that the special rotational deformation and the relative shear modulus of the upper the lower half plane have great effect on the lattice dislocation emission from the interface collinear crack tip.

The effect of defect orientation and size on glenohumeral instability: a biomechanical analysis.

The purpose of this study was to determine the relationship between bony stability and percentage of anterior glenoid bone loss and the effect of bone loss orientation. Twelve cadaveric shoulders were studied. Glenoid bone defects were simulated in two different osteotomy angles: 0° and 45° to the superoinferior (SI) axis of the glenoid. The force and displacement required for dislocation were measured under two compressive forces of 40 and 60N. Testing was performed for the intact glenoid and glenoid defects of 2, 4, 6, 8, and 10 mm from the anterior margin. The maximum force for dislocation with the 2-mm glenoid defect was significantly decreased compared with intact glenoid (p = 0.01), and this force also significantly decreased with each increase in defect size (p < 0.05). The dislocation force for 45° osteotomy was significantly higher than that for 0° osteotomy for all defect widths up to 8 mm with 40N compression and 6 mm with 60N compression (p < 0.001). The displacement at dislocation did not significantly decrease until the 8-mm defect with the 45° osteotomy but significantly decreased with the 4-mm defect with the 0° osteotomy. The required force for dislocation with 60N compression was significantly higher than that with 40N compression for all osteotomy sizes and orientations. The decrease in stability even with glenoid bone loss as small as 2 mm or 7.5 % of the glenoid width suggests that bony restoration is recommended whenever any bone loss exists. Bone defects parallel to SI axis may be more susceptible to recurrent instability, and shoulder muscle strengthening exercises may increase glenohumeral compressive force and thus improve glenohumeral stability. Bony restoration is recommended whenever bone loss exists even with small bone fragments particularly those in line with the superior-inferior axis of the glenoid.

Interaction among &lt;i&gt;n&lt;/i&gt; Parallel Dislocations in One-Dimensional Hexagonal Quasicrystals

By means of analytic function theory, the problems of interaction amongparallel dislocations in one-dimensional hexagonal quasicrystals are investigated. The interaction force of parallel dislocations in the material is obtained in forms of complex variable function firstly, which is the versions of well-known Peach-Koehler formula in one-dimensional hexagonal quasicrystals on parallel dislocations. These results are development of the corresponding parts of quasicrystals. Meanwhile, in this paper, we firstly give the equivalent action point of parallel dislocations in one-dimensional hexagonal quasicrystals, which be of important reference value to researching the interaction problems of many dislocations in fracture mechanics of quasicrystals.