Finite Element Analysis of Coronal Shear Fractures of the Femoral Neck: Displacement of the Femoral Head and Effect of Osteosynthetic Implants

Coronal shear fractures of the femoral neck (CSFF) are the most challenging to treat among proximal femur fractures, directly affecting the life expectancy of patients with osteoporosis. However, an adequate osteosynthesis method has not been elucidated yet. This study investigated the displacement direction of the femoral head fragment and its effect on the bone using finite element method. A finite element model for CSFF was developed from CT image data of a patient with osteoporosis using Mechanical Finder (ver. 11). Subsequently, finite element analyses were performed on six osteosynthesis models under maximum load applied during walking. The compressive stresses, tensile stresses, and compressive strains of each model were examined. The results suggested that the compressive and tensile stress distributions were concentrated on the anterior side of the femoral neck. Compressive strain distribution in the femoral head and neck was concentrated in four areas: at the tip of the blade or lag screw, the anteroinferior side of the blade or lag screw near the fracture site, and the upper right and lower left near the junction of the blade or lag screw and nail. Thus, the distribution of both these stresses revealed that the femoral head fragment was prone to anterior and inferior displacement. Distribution of compressive strains revealed the direction of the stress exerted by the osteosynthetic implant on the bone. The same results were observed in all osteosynthetic implants;thus, the findings could lay the foundation for developing methods for placing osteosynthetic implants less prone to displacement and the osteosynthetic implants themselves. In particular, the study provides insight into the optimal treatment of CSFF.

Intelligent method to experimentally identify the fracture mechanism of red sandstone

Tensile and shear fractures are significant mechanisms for rock failure.Understanding the fractures that occur in rock can reveal rock failure mechanisms.Scanning electron microscopy(SEM)has been widely used to analyze tensile and shear fractures of rock on a mesoscopic scale.To quantify tensile and shear fractures,this study proposed an innovative method composed of SEM images and deep learning techniques to identify tensile and shear fractures in red sandstone.First,direct tensile and preset angle shear tests were performed for red sandstone to produce representative tensile and shear fracture surfaces,which were then observed by SEM.Second,these obtained SEM images were applied to develop deep learning models(AlexNet,VGG13,and SqueezeNet).Model evaluation showed that VGG13 was the best model,with a testing accuracy of 0.985.Third,the features of tensile and shear fractures of red sandstone learned by VGG13 were analyzed by the integrated gradient algorithm.VGG13 was then implemented to identify the distribution and proportion of tensile and shear fractures on the failure surfaces of rock fragments caused by uniaxial compression and Brazilian splitting tests.Results demonstrated the model feasibility and suggested that the proposed method can reveal rock failure mechanisms.

Mechanical Properties,Damage and Fracture Mechanisms of Bulk Metallic Glass Materials

The deformation, damage, fracture, plasticity and melting phenomenon induced by shear fracture were investigated and summarized for Zr-, Cu-, Ti- and Mg-based bulk metallic glasses （BMGs） and their composites. The shear fracture angles of these BMG materials often display obvious differences under compression and tension, and follow either the Mohr-Coulomb criterion or the unified tensile fracture criterion. The compressive plasticity of the composites is always higher than the tensile plasticity, leading to a significant inconsistency. The enhanced plasticity of BMG composites containing ductile dendrites compared to monolithic glasses strongly depends on the details of the microstructure of the composites. A deformation and damage mechanism of pseudo-plasticity, related to local cracking, is proposed to explain the inconsistency of plastic deformation under tension and compression. Besides, significant melting on the shear fracture surfaces was observed. It is suggested that melting is a common phenomenon in these materials with high strength and high elastic energy, as it is typical for BMGs and their composites failing under shear fracture. The melting mechanism can be explained by a combined effect of a significant temperature rise in the shear bands and the instantaneous release of the large amount of elastic energy stored in the material.

Effects of Shear Fracture on In-depth Profile Modification of Weak Gels

Two sand packs were filled with fine glass beads and quartz sand respectively. The characteristics of crosslinked polymer flowing through the sand packs as well as the influence of shear fracture of porous media on the indepth profile modification of the weak gel generated from the crosslinked polymer were investigated. The results indicated that under the dynamic condition crosslinking reaction happened in both sand packs, and the weak gels in these two cases became small gel particles after water flooding. The differences were： the dynamic gelation time in the quartz sand pack was longer than that in the glass bead pack. Residual resistance factor （FRR） caused by the weak gel in the quartz sand pack was smaller than that in the glass bead pack. The weak gel became gel particles after being scoured by subsequent flood water. A weak gel with uniform apparent viscosity and sealing characteristics was generated in every part of the glass bead pack, which could not only move deeply into the sand pack but also seal the high capacity channels again when it reached the deep part. The weak gel performed in-depth profile modification in the glass bead pack, while in the quartz sand pack, the weak gel was concentrated with 100 cm from the entrance of the sand pack. When propelled by the subsequent flood water, the weak gel could move towards the deep part of the sand pack but then became tiny gel particles and could not effectively seal the high capacity channels there. The in-depth profile modification of the weak gel was very weak in the quartz sand pack. It was the shear fracture of porous media that mainly affected the properties and weakened the in-depth profile modification of the weak gel.

Deformation Localization and Shear Fracture of a Rapidly Solidified Al-Fe-V-Si Alloy at Elevated Temperature

The tensile and fatigue behavior of a dispersoid strengthened, powder metallurgy Al-Fe-V-Si alloy at ambient and elevated temperatures was investigated. The results show that the strength and ductility of the alloy decrease significantly with increasing temperature and decreasing strain rate. Micro-structural examinations reveal that this change in mechanical behavior with increasing temperature is related to the mode of deformation of the alloy. Further observations show that localized shear deformation is responsible for the losses in both strength and ductility of the alloy at elevated temperature.

DEFORMATION LOCALIZATION AND SHEAR BAND FRACTURE IN STRONG ANISOTROPY SHEET TENSION

The tensile deformation localization and the shear band fracture behaviors of sheet metals with strong anisotropy are numerically simulated by using Updating Lagrange finite element method, Quasi-how plastic constitutive theory([1]) and B-L planar anisotropy yield criterion([2]). Simulated results are compared with experimental ones. Very good consistence is obtained between numerical and experimental results. The relationship between the anisotropy coefficient R and the shear band angle theta is found.

Lateral epicondyle osteotomy approach for coronal shear fractures of the distal humerus:Report of three cases and review of the literature

BACKGROUND Coronal shear fractures of the distal humerus are rare injuries and are technically challenging to manage.Open reduction and internal fixation(ORIF)has become the preferred treatment because it provides anatomical reduction,stable internal fixation,and early motion,but the optimal surgical approach remains controversial.CASE SUMMARY We report three cases of coronal shear fractures of the distal humerus treated successfully by ORIF via a novel surgical approach,in which lateral epicondyle osteotomy was performed based on the extended lateral approach.We named the novel surgical approach the lateral epicondyle osteotomy approach.All patients underwent surgical treatment and were discharged successfully.All patients had excellent functional results according to the Mayo elbow performance score.The average range of motion was 118°in flexion/extension and 172°in pronation/supination.Only case 2 had a complication,which was implant prolapse.CONCLUSION We demonstrated that the lateral epicondyle osteotomy approach in ORIF is effective and safe for coronal shear fractures of the distal humerus.

ROCK FRACTURE PROCESS ZONE AND ITS INFLUENCE ON MODEⅡFRACTURE BEHAVIOR

On the basis of that rock material usually has a larger fracture process zone,a new fracture criterion which is different from that of linear elastic fracture theory was presented.On this basis,the fracture behavior and influencing factors under modeⅡor compressive shear loading were investigated.

Stresses and Shear Fracture Zone of Jinshazhou Tunnel Surrounding Rock in Rich Water Region

Field evidence has shown that large-scale and unstable discontinuous planes in the rock mass surrounding tunnels in rich water region are probably generated after excavation. The tunnel surrounding rock was divided into three zones, including elastic zone, plastic damage zone and shear fracture zone for assessing the stability of the tunnel surrounding rock. By local hydrogeology, the stresses of surrounding rock of Jinshazhou circular tunnel was analyzed and the stress solutions on the elastic and plastic damage zones were obtained by applying the theories of fluid-solid coupling and elasto-plastic damage mechanics. The shear fracture zone generated by joints was studied and its range was determined by using Molar-Coulomb strength criterion. Finally, the correctness of the theoretical results was validated by comparing the scopes of shear fracture zones calculated in this paper with those from literature.

Nano-refinement of the face-centered cubic Zr(Fe,Cr)_(2)secondary phase particles in Zircaloy-4 alloy via localized-shearing/bending-driven fracture under high-temperature compression

Nanoparticles are extensively introduced to improve the mechanical,physical,and chemical properties of alloys.In the present study,the underlying nano-refinement mechanisms of face-centered cubic Zr(Fe,Cr)_(2)secondary phase particles(SPPs)that precipitated in Zircaloy-4 alloy under high-temperature compression were investigated in detail by utilizing high-resolution transmission electron microscopy(HRTEM)and conventional TEM techniques.The frequently observed Zr(Fe,Cr)_(2)SPPs were incoherent with the matrix and exhibited brittle fracture behaviors without measurable plasticity.HRTEM observations revealed two mechanisms underlying the nano-refinement of incoherent micro-sized SPPs via localized shear fracture on{11¯2}SPP and nanoprecipitate-assisted bending fracture,respectively.The latter was,for the first time,found to occur when the movements of large SPPs were blocked by nanometer-sized SPP during alloy deformation.Accordingly,two force models were proposed to visualize their potential nano-refinement processes.The knowledge attained from this study sheds new light on the deformation behaviors of Zr(Fe,Cr)_(2)SPPs and their associated size refinement mechanisms under high-temperature compression,and is expected to greatly benefit the process optimization of zirconium alloys to achieve precipitate nano-refinement.

Laboratory visualization of damage asymmetry formation of rock fracture via acoustic emission and digital imaging correlation

Rock fracture mechanics and accurate characterization of rock fracture are crucial for understanding a variety of phenomena interested in geological engineering and geoscience.These phenomena range from very large-scale asymmetrical fault structures to the scale of engineering projects and laboratory-scale rock fracture tests.Comprehensive study can involve mechanical modeling,site or post-mortem investigations,and inspection on the point cloud of the source locations in the form of earthquake,microseismicity,or acoustic emission.This study presents a comprehensive data analysis on characterizing the forming of the asymmetrical damage zone around a laboratory mixed-mode rock fracture.We substantiate the presence of asymmetrical damage through qualitative analysis and demonstrate that measurement uncertainties cannot solely explain the observed asymmetry.The implications of this demonstration can be manifold.On a larger scale,it solidifies a mechanical model used for explaining the contribution of aseismic mechanisms to asymmetrical fault structures.On a laboratory scale,it exemplifies an alternative approach to understanding the observational difference between the source location and the in situ or post-mortem inspection on the rock fracture path.The mechanical model and the data analysis can be informative to the interpretations of other engineering practices as well,but may face different types of challenges.

Study on adhesively-bonded surface of tapered double cantilever specimen made of aluminum foam affected with shear force

Aluminum foam is widely used in diverse areas to minimize the weight and maximize the absorption of shock energy in lightweight structures and various bio-materials.It presents a number of advantages,such as low density,incombustibility,non-rigidity,excellent energy absorptivity,sound absorptivity and low heat conductivity.The aluminum foam with an air cell structure was placed under the TDCB Mode II tensile load by using Landmark equipment manufactured by MTS to examine the shear failure behavior.The angle of the tapered adhesively-bonded surfaces of specimens was designated as a variable,and three models were developed with the inclined angles differing from one another at 6°,8° and 10°.The specimens with the inclined angles of 6°,8° and 10° have the maximum reaction forces of 168 N,194 N when the forced displacements are 6,5 and 4.2 mm respectively.There are three specimens with the inclined angles of 10°,8° and 6° in the order of maximum reaction force.As the analysis result,the maximum equivalent stresses of 0.813 MPa and 0.895 MPa happened when the forced displacements of 6 mm and 5 mm proceeded at the models of 6° and 8°,respectively.A simulation was carried out on the basis of finite element method and the experimental design.The results of the experiment and the simulation analysis are shown not different from each other significantly.Thus,only a simulation could be confirmed to be performed in substitution of an experiment,which is costly and time-consuming in order to determine the shearing properties of materials made of aluminum foam with artificial data.

Mechanical Properties of Deep-buried Marble Material Under Loading and Unloading Tests

The mechanical properties are essentially different when rock material is subjected to loading or unloading conditions. In this study, loading and unloading tests with various confining pressures are conducted to investigate the mechanical properties of marble material samples taken from the deep diversion tunnels of Jinping II Hydropower Station. The stress-strain relationship, failure characteristics and strength criterion are compared and analyzed based on the experiment results. The results show： in the loading and unloading test, peak strength, lateral strain, axial strain and plastic deformation increase significantly as the confining pressure increases. Lateral strain increased significantly and obvious lateral dilatancy can be observed to the change of confining pressure; The fracture mode is mainly the single shear fracture for the triaxial compression test and post-peak test, angle between the failure surface and the ends of the rock material becomes smaller as the confining pressure increases. Hock-Brown strength criterion reflects the strength characteristics of marble material under two different unloading conditions, and has some supplementary effects to the rock material of mechanical field.

Stress-state dependence of dynamic strain aging:Thermal hardening and blue brittleness

This study aims to discover the stress-state dependence of the dynamic strain aging(DSA)effect on the deformation and fracture behavior of high-strength dual-phase(DP)steel at different deformation temperatures(25-400°C)and reveal the damage mechanisms under these various configurations.To achieve different stress states,predesigned specimens with different geometric features were used.Scanning electron microscopy was applied to analyze the fracture modes(e.g.,dimple or shear mode)and underlying damage mechanism of the investigated material.DSA is present in this DP steel,showing the Portevin-Le Chatelier(PLC)effect with serrated flow behavior,thermal hardening,and blue brittleness phenomena.Results show that the stress state contributes distinctly to the DSA effect in terms of the magnitude of thermal hardening and the pattern of blue brittleness.Either low stress triaxiality or Lode angle parameter promotes DSA-induced blue brittleness.Accordingly,the damage mechanisms also show dependence on the stress states in conjunction with the DSA effect.

LONGITUDINAL SHEAR PROBLEMS OF COLLINEAR RIGID LINE INCLUSIONS IN ANISOTROPIC MATERIALS

Longitudinal shear problems of collinear rigid line inclusions (sometimes calledhard crack or inverse crack problems) in anisotropic materials are dealt with. By usingthe conplex variable method, we present the formulation of the general problem and the closed form solutions to some problems of practical importance, The atressdistribution in the immediate vicinity of the rigid line end is examined. The corresponding formulation and solutions for isotropic materials can be arrived at fromthe special cases of those in the present paper, some of which are in agreement with the existing results￣[1].

Characteristics of New-type Energy Absorber for Vehicle Collision

A new type energy absorber was introduced,which is composed of thousands of thin ring plates with different diameters.Because it can switch the impact to thousands of shearing actions among thin ring plates inside the absorber,the impact energy is decentralized and dissipated gradually,the impact acting time is extended and the peak of acceleration is reduced obviously.Numerical simulations by finite element method (FEM) coupled with smoothed particle hydrodynamics (SPH) method were preformed to predict the energy absorption characteristics.Energy absorption ability with different impact velocities was studied and the effects of thickness and material of ring plates were discussed.The sled crash test was carried out to validate the result of simulations.The new type absorber is effective for collision that impact velocity is lower than 40 km/h.

Experimental study on the mechanism of non-synchronism of seismo-electromagnetic radiation precursors

In order to investigate the physical mechanism of non-synchronism of seismo-electromagnetic radiation precursors, we have made shear fracture and frictional sliding tests of rock samples by loading them in biaxial compression to model the activity of tectonic fault zones in seismogenic region. By installing antennae of different frequency responses and acoustic transducers around the fracture surface, the signals of electromagnetic radiation and acoustic emission in different directions and of different frequencies produced by rock samples during their shear fracturing and frictional sliding have been recorded by an automatic, high-speed and continuous observation system. Some implications given by the experimental results are as follows. (1) During the process of shear fracturing and frictional sliding of rock samples under biaxial compression, large amounts of electromagnetic signals are produced; their frequencies range from several hundred Hz to several thousand Hz. (2) Signals received by antennae in different directions and of different frequencies are non-synchronous. They differ in amplitude from one another, with the signal received by antennae nearest to the fracture surface being the maximum. (3) Electric signals and magnetic signals do not appear synchronously; among them, electric signals appear more frequently and are of larger amplitude. The authors hold that electric signals (E) and magnetic signals (M) are of different genetic mechanisms: electric signals from inside the rock sample are produced by the piezoelectric effect of rock-forming crystals and net electric charge produced by the newly created surfaces due to rock fracture, whereas magnetic signals are produced by the high-speed motion of charged rock fragments and the ionization of ambient air excited by electrons emitted by rock in fracturing. Analysis shows that in some moderately strong earthquakes the electric and magnetic signals also showed the phenomenon of non-synchronism: the electric signal was earlier than the magnetic signal. If the same station observes simultaneously the electric field (underground) and magnetic field (air), the efficiency of earthquake prediction by seismo-electromagnetic radiation precursors would be raised effectively.

Effect of Porous Copper Pore Density on Joint Interface:Microstructure and Mechanical Analysis

The effect of the pore density of porous copper(Cu)on brazed Cu/porous Cu was investigated.A filler with a composition of Cu⁃9.0Sn⁃7.0Ni⁃6.0P(Sn:Tin;Ni:Nickel;P:Phosphorus)and porous Cu with pore densities of 15 pores per inch(PPI),25 PPI,and 50 PPI were employed.The joint strength of Cu/porous Cu was evaluated with shear tests at different brazing temperatures.Characterizations of the joint interface and fractured surface were achieved with scanning electron microscope(SEM),energy dispersive X⁃ray spectroscopy(EDX),and X⁃ray diffraction(XRD).The micro⁃hardness test of Cu/porous Cu joint interface showed a high hardness value(HV)for 50 PPI porous Cu.This result was in line with its low shear strength.It was proved that the joint strength of Cu/porous Cu is dependent on the pore density of the porous Cu structure and brittle phases of Cu_(3)P and Ni_(3)P in the brazed interface.

Shear Fracture of Advanced High Strength Steels

Failure experiments were carried out through a stretch-bending test system for advanced high strength steels, i.e. dual-phase （DP） steels and martensitic steels （MS）. The die radius in this system was designed from 1 to 15 mm to investigate the failure mode under different geometries. Two failure modes were observed during the ex- periments. As a result, critical relative radii （the ratio of inner bending radius R to sheet thickness t） for DP590 and DP780 steels were obtained. The stretch-bending tests of DP980 display some trends unlike DP590 and DP780 steels, and curve of DP980 in different thicknesses does not coincide well. High blank holder force exhibits more possibility of shear fracture tendency than low blank holder force. The unique character of high strength martensitic steel （1500MS） is that no shear fracture is found especially over small bending radius （R =2 mm） under the same experi- mental conditions. Microstructure analysis indicates that there are obviously elongated grains on shear fracture sur- face. It shows smaller diameter and shallower depth of the dimples than the necking failure.

On the material dependence of experimental shear fracture orientation

It is not uncommon to observe shear fractures in ductile rocks oriented at more than 45° with respect to the maximum compression direction. Since these orientations cannot be explained with the classic Mohr-Coulumb or Tresca yield criteria, Zheng et al.(Journal of Structural Geology, 35: 1394–1405, 2011) proposed the maximum effective moment(MEM) failure criterion. This rule suggests that shear fractures in ductile rocks form at ?55° with the maximum compression axis and that this orientation is material-independent and, therefore, universal. Zheng et al.(Science China: Earth Sciences, 57(11): 2819–2824, 2014) used data from our own experiments as supporting evidence of their failure criterion. In this contribution we discuss why shear fracture formation in ductile rocks indeed strongly depends on the mechanical properties of the deforming medium, and why experimental data should not be taken to prove the validity of the MEM criterion. The formation mechanisms and orientations of shear fractures in our experiments significantly vary depending on the material strength and degree and type of anisotropy(composite and intrinsic). We therefore demonstrate using experimental data that a universal failure angle in ductile and anisotropic rocks does not apply. Additionally, we highlight some inconsistencies of the MEM criterion.