Bending Rotation Research Articles

A comparative study of the effect of facet tropism on the index-level kinematics and biomechanics after artificial cervical disc replacement (ACDR) with Prestige LP, Prodisc-C vivo, and Mobi-C: a finite element study

IntroductionArtificial cervical disc replacement (ACDR) is a widely accepted surgical procedure in the treatment of cervical radiculopathy and myelopathy. However, some research suggests that ACDR may redistribute more load onto the facet joints, potentially leading to postoperative axial pain in certain patients. Earlier studies have indicated that facet tropism is prevalent in the lower cervical spine and can significantly increase facet joint pressure. The present study aims to investigate the changes in the biomechanical environment of the cervical spine after ACDR using different prosthese when facet tropism is present.MethodsA C2-C7 cervical spine finite element model was created. Symmetrical, moderate asymmetrical (7 degrees tropism), and severe asymmetrical (14 degrees tropism) models were created at the C5/C6 level by adjusting the left-side facet. C5/C6 ACDR with Prestige LP, Prodisc-C vivo, and Mobi-C were simulated in all models. A 75 N follower load and 1 N⋅m moment was applied to initiate flexion, extension, lateral bending, and axial rotation, and the range of motions (ROMs), facet contact forces(FCFs), and facet capsule stress were recorded.ResultsIn the presence of facet tropism, all ACDR models exhibited significantly higher FCFs and facet capsule stress compared to the intact model. In the asymmetric model, FCFs on the right side were significantly increased in neutral position, extension, left bending and right rotation, and on both sides in right bending and left rotation compared to the symmetric model. All ACDR model in the presence of facet tropism, exhibited significantly higher facet capsule stresses at all positions compared to the symmetric model. The stress distribution on the facet surface and the capsule ligament in the asymmetrical models was different from that in the symmetrical model.ConclusionsThe existence of facet tropism could considerably increase FCFs and facet capsule stress after ACDR with Prestige-LP, Prodisc-C Vivo, and Mobi-C. None of the three different designs of implants were able to effectively protect the facet joints in the presence of facet tropism. Research into designing new implants may be needed to improve this situation. Clinical trials are needed to validate the impact of facet tropism.

Combined effect of artificial cervical disc replacement and facet tropism on the index-level facet joints: a finite element study

BackgroundArtificial Cervical Disc Replacement (ACDR) is an effective treatment for cervical degenerative disc diseases. However, clinical information regarding the facet joint alterations after ACDR was limited. Facet tropism is common in the sub-axial cervical spine. Our previous research indicated that facet tropism could lead to increased pressure on the cervical facet joints. This study aimed to assess the impact of facet tropism on the facet contact force and facet capsule stress after ACDR.MethodsA C2–T1 cervical finite element model was constructed from computed tomography (CT) scans of a 28-year-old male volunteer. Symmetrical, moderate asymmetrical (7 degrees tropism), and severe asymmetrical (14 degrees tropism) models were created at the C5/C6 level by altering the facet orientation at the C5-C6 level. The C5/C6 ACDR was simulated in the intact, moderate asymmetrical and severe asymmetrical models. A 75-N follower load with 1.0-Nm moments was applied to the top of C2 vertebra in the models to simulate flexion, extension, lateral bending, and axial rotation with the T1 vertebra fixed. The range of motions (ROMs) under all moments, facet contact forces (FCFs) and facet capsule strains were tested.ResultsIn the asymmetrical model, the right FCFs considerably increased under flexion, extension, right bending, left rotation, especially under right bending the right sided FCF of the severe asymmetrical model was about 5.44 times of the neutral position, and 3.14 times of the symmetrical model. and concentrated on the cephalad part of the facets. The facet capsule stresses on both sides remarkably increased under extension, lateral bending and right rotation. In the moderate and severe asymmetrical models, the capsule strain was greater on both sides of each position than in the symmetric model.ConclusionsThe face tropism increased facet contact force and facet capsule strain after ACDR, especially under extension, lateral bending, and rotation, and also could result in abnormal stress distribution on the facet joint surface and facet joint capsule. The results suggest that face tropism might be a risk factor for post-operative facet joint degeneration progression after ACDR. Facet tropism may be noteworthy when ACDR is considered as a surgical option.

Development of a spinopelvic complex finite element model for quantitative analysis of the biomechanical response of patients with degenerative spondylolisthesis.

Research on degenerative spondylolisthesis (DS) has focused primarily on the biomechanical responses of pathological segments, with few studies involving muscle modelling in simulated analysis, leading to an emphasis on the back muscles in physical therapy, neglecting the ventral muscles. The purpose of this study was to quantitatively analyse the biomechanical response of the spinopelvic complex and surrounding muscle groups in DS patients using integrative modelling. The findings may aid in the development of more comprehensive rehabilitation strategies for DS patients. Two new finite element spinopelvic complex models with detailed muscles for normal spine and DS spine (L4 forwards slippage) modelling were established and validated at multiple levels. Then, the spinopelvic position parameters including peak stress of the lumbar isthmic-cortical bone, intervertebral discs, and facet joints; peak strain of the ligaments; peak force of the muscles; and percentage difference in the range of motion were analysed and compared under flexion-extension (F-E), lateral bending (LB), and axial rotation (AR) loading conditions between the two models. Compared with the normal spine model, the DS spine model exhibited greater stress and strain in adjacent biological tissues. Stress at the L4/5 disc and facet joints under AR and LB conditions was approximately 6.6 times greater in the DS spine model than in the normal model, the posterior longitudinal ligament peak strain in the normal model was 1/10 of that in the DS model, and more high-stress areas were found in the DS model, with stress notably transferring forwards. Additionally, compared with the normal spine model, the DS model exhibited greater muscle tensile forces in the lumbosacral muscle groups during F-E and LB motions. The psoas muscle in the DS model was subjected to 23.2% greater tensile force than that in the normal model. These findings indicated that L4 anterior slippage and changes in lumbosacral-pelvic alignment affect the biomechanical response of muscles. In summary, the present work demonstrated a certain level of accuracy and validity of our models as well as the differences between the models. Alterations in spondylolisthesis and the accompanying overall imbalance in the spinopelvic complex result in increased loading response levels of the functional spinal units in DS patients, creating a vicious cycle that exacerbates the imbalance in the lumbosacral region. Therefore, clinicians are encouraged to propose specific exercises for the ventral muscles, such as the psoas group, to address spinopelvic imbalance and halt the progression of DS.

Prediction of rotational bending fatigue life of bearing steel based on damage mechanics

Based on the theory of continuous damage mechanics, this paper proposes a fatigue damage evolution model and numerical calculation method considering the influence of vacuum chemical heat treatment process, and studies the rotational bending fatigue damage analysis and life prediction method of M50NiL bearing steel. Firstly, the constitutive model, fatigue damage evolution equation and material parameter calibration method in the theoretical model are given. Secondly, based on the ABAQUS platform, the damage mechanics-finite element numerical calculation method of fatigue damage analysis considering the influence of hardened layer is realized by writing the UMAT subroutine; then, the rotational bending fatigue test of M50NiL bearing steel treated by vacuum chemical heat treatment of quenching and tempering, carburizing and carbonitriding is carried out, and the influence of heat treatment process on fatigue performance is analyzed; finally, based on the proposed fatigue damage model and numerical calculation method, the rotational bending fatigue life of M50NiL bearing steel is predicted, and the results are compared with the experimental results to verify the correctness of the proposed method.

Finite element analysis of biomechanical investigation on diverse internal fixation techniques in oblique lumbar interbody fusion

BackgroundTo establish a three-dimensional finite element model of the lumbar spine and investigate the impact of different fixation techniques on the biomechanical characteristics of oblique lumbar interbody fusion (OLIF).MethodsThe study aimed to establish and validate a comprehensive three-dimensional model of the lower lumbar spine (L3-S1) using the finite element method. L4-L5 was selected as the surgical segment, and four distinct OLIF surgical models were constructed: Stand-alone (SA), unilateral cortical bone trajectory screw (UCBT), bilateral cortical bone trajectory screw (BCBT), and bilateral pedicle screw (BPS). The models were underwent a pure moment of 10N·m to simulate lumbar extension, flexion, left bending, right bending, left and right rotation movements. Subsequently, the range of motion (ROM), cage stress, and fixation stress were calculated.ResultsIn the L3-L5 segment, the BCBT group showed the most limited range of motion (ROM) under exercise load, indicating superior stability within this group. The ROM and cage stress values were found to be highest in the SA group. In contrast, the cage and internal fixation stress in the BPS group were observed to be lowest (9.91 ~ 53.83MPa, 44.93 ~ 84.85 MPa). With the exception of right bending and right rotation, the UCBT group demonstrated higher levels of internal fixation stress (102.20 ~ 164.62 MPa).ConclusionsThe study found that OLIF-assisted internal fixation improved segmental stability and reduced cage stress. The BPS group had advantages over the CBT group in preventing endplate damage and reducing the risk of cage subsidence. However, BCBT group has distinct merits in maintaining surgical segment stability, distributing stress load on the spinal motor unit, and reducing the likelihood of adjacent segment degeneration (ASD).

Finite element analysis shows minimal stability difference between individualized mini-hemilaminectomy-corpectomy and partial lateral corpectomy in a dog model.

Use finite element analysis to evaluate the biomechanical effects of spinal decompression procedures in healthy Beagle dogs, comparing individualized mini-hemilaminectomy-corpectomy (iMHC), mini-hemilaminectomy, partial lateral corpectomy (PLC), and hemilaminectomy. A finite element model of the L1-L2 functional spinal unit was generated using CT data. For each decompression model, loads were applied in 0.2-Nm steps (maximum, 2.0 Nm) in 6 directions: flexion, extension, right and left lateral bending, and right and left axial rotation. The L1 spinous process tip displacement angle was quantified numerically. Among the 4 techniques, mini-hemilaminectomy exhibited the smallest displacement angles across all directions. Hemilaminectomy exhibited the largest displacement angles in extension, flexion, right rotation, and left rotation across all techniques. Left and right lateral bending displacement angles were marginally larger for iMHC than for hemilaminectomy at 0.4 Nm; however, at 2.0 Nm, displacement angles were similar. Mini-hemilaminectomy minimizes functional spinal unit instability to the greatest extent. Hemilaminectomy is more unstable than iMHC and PLC in flexion, extension, and rotation. Mini-hemilaminectomy-corpectomy and PLC are more unstable than hemilaminectomy in lateral bending, with iMHC being slightly more unstable than PLC or nearly equal. Mini-hemilaminectomy minimizes instability to the greatest extent in cases of ventrolateral spinal compression. In cases of ventral spinal compression, iMHC may be preferable to PLC for providing equivalent stability without impeding spinal cord visualization, but both techniques can cause instability depending on loading direction, so careful attention to postoperative instability is necessary when excessive vertebral body resection is involved.

Prediction of rotational bending fatigue life of bearing steel based on damage mechanics

Based on the theory of continuous damage mechanics, this paper proposes a fatigue damage evolution model and numerical calculation method considering the influence of vacuum chemical heat treatment process, and studies the rotational bending fatigue damage analysis and life prediction method of M50NiL bearing steel. Firstly, the constitutive model, fatigue damage evolution equation and material parameter calibration method in the theoretical model are given. Secondly, based on the ABAQUS platform, the damage mechanics-finite element numerical calculation method of fatigue damage analysis considering the influence of hardened layer is realized by writing the UMAT subroutine; then, the rotational bending fatigue test of M50NiL bearing steel treated by vacuum chemical heat treatment of quenching and tempering, carburizing and carbonitriding is carried out, and the influence of heat treatment process on fatigue performance is analyzed; finally, based on the proposed fatigue damage model and numerical calculation method, the rotational bending fatigue life of M50NiL bearing steel is predicted, and the results are compared with the experimental results to verify the correctness of the proposed method.

Rotation bending high cycle fatigue behaviors of TC21 alloy with bimodal microstructure

The TC21 alloy has been extensively utilized in the aerospace structural components, making it crucial to investigate the fatigue damage mechanism of this alloy. In this study, a comprehensive investigation was conducted into the high-cycle fatigue damage mechanism of TC21 alloy under rotation bending, considering variations in primary equiaxed α (αp) phase contents and size in bimodal microstructure (BM). Results demonstrate that the TC21 alloy exhibits optimal strength-ductility and fatigue life at approximately 25 percent of the αp phase content. The content and dimension of the αp phase play a significant role in regulating the onset of fatigue fractures. Dislocation pile-up around the αp phase promotes the formation of microvoids and microcracks. Notably, when the content of the αp phase falls below 15%, there is an increased influence from secondary α phase (αs) on crack initiation. Moreover, excessive amounts of αp coupled with decreased size lead to a reduction in fatigue life. The aforementioned factors contribute to an intensified concentration of stress, facilitate a more uniform path for crack extension, and expedite the rate of fatigue crack propagation.

Comparison of a Novel Posterior Integrated Transfixation Sacroiliac Joint Fusion Approach to the Posterolateral and Lateral Approaches: A Cadaveric Biomechanical and Computational Analysis of the Fixation, Invasiveness, and Fusion Area.

To concurrently assess and compare the fixation efficacy, invasiveness, and fusion potential of a posterior integrated transfixation cage system to the posterolateral threaded implant and lateral triangular rod systems, in a cadaveric model. Twelve (12) cadaveric sacroiliac joint specimens were utilized and tested within the single-leg stance multidirectional pure moment bending model. Each specimen was tested in the intact, destabilized, treated (using posterior, posterolateral, and lateral systems), and post-fatigue conditions by applying 0 to ± 7.5 Nm of moment in flexion-extension, axial rotation, and lateral bending while measuring the angular range of motion between the sacrum and ilium. Computational models were reconstructed from Computed Tomography (CT) scans and manufacturer surgical technique guides. The models were utilized to quantify the volume of bone removed during implantation and the surface area available for fusion. The posterior integrated transfixation cage system and the lateral triangular rods produced equivalent motion reduction in all motion planes (P > 0.583). The posterolateral cylindrical threaded implant produced less motion reductions than the posterior and lateral implants in flexion-extension (6% ± 3% vs 37% ± 10% and 33% ± 11%, respectively, P <0.05). The posterior system removed 22%-60% less bone volume from the sacrum and ilium (P<0.10), introduced 200%-270% more implant surface to the joint space (P<0.01) and decorticated 75%-375% more joint surface area (P<0.01). The posterior integrated transfixation single-implant cage system is superior to the posterolateral cylindrical threaded single-implant system. Its performance in osteopenic bone is equivalent to the lateral triangular rod system in healthy bone; however, the posterior integrated transfixation cage system requires a single implant, while the lateral triangular rod system requires three. The posterior implant removes the least bone volume and has the most surface area for fusion, providing a significantly better opportunity for robust sacroiliac joint arthrodesis.

Defects in Rotary Draw Bending and Their Effects on Formability

Tube with different quantities and types; It can be described as a long and narrow cylinder with open ends, which carries liquids, gases and similar substances from one place to another. Tubes are used for advancements in sectors such as transportation, automobiles and aerospace. Aluminum, Inconel and titanium materials are decided according to the required needs in the design and production of tubes. There are different production methods to give permanent shape to the tubes. During tube bending operations, the feasibility of tube bending varies depending on the material type, bending angles, bending radius, tools and process. The tubes produced with a certain margin of defect. Some defects occur during and after production. Springback, ovality, breakage and tearing are among these defects. These defects may prevent the system to be replaced from flowing with the desired properties, as well as the installation of the produced tubes. The aviation and space fields, the production of tubes with high strength and complex geometries is critical. Errors that occur in the rotary draw bending process, one of these pipe bending methods, and the steps to prevent these errors are compiled and presented.

Numerical and experimental investigations on influence of spherical hinge mandrel on deformation characteristics of large diameter tube in small-radius NC rotary bending

Numerical and experimental investigations on influence of spherical hinge mandrel on deformation characteristics of large diameter tube in small-radius NC rotary bending

Peanut Pickup Combine Harvester Seedling Vines Crushing Mechanism Performance Enhancement and Pilot Studies

Aiming at the current peanut pickup combine harvester seedling vines crushing mechanism operation qualified seedling length rate is low, the impurity rate is high, and the seedling vines crushing mechanism is optimized design. On the basis of the material characteristics of peanut seedling vines, taking the crushing mechanism as the research carrier, the interaction mechanism of the seedling vine mechanism was analyzed. Establish the mechanical model and motion trajectory model in the crushing process, simulate the peanut seedling vines crushing process based on the discrete element method, analyze the influence of the cutter shaft rotational speed, movement speed, and bending angle on the crushing of peanut seedling vines, and establish the regression model, and the results of the research show that the influence factors in the main order of priority are: knife shaft speed &gt; movement speed &gt; bending angle The optimal parameter combination is knife shaft speed 2171.94 r/min, movement speed 0.79 m/s, and bending angle 45°. According to the field test conditions, it is determined that the knife shaft rotational speed of 2170 r/min, movement speed of 0.8 m/s, and bending angle of 45° can make the peanut seedling vines crushing mechanism of the work performance to achieve a qualified seedling length rate of 97.292%, the rate of impurity content of 2.746%, and the error with the predicted value is less than 2%, which indicates that this study can provide a reference for the optimal design of the seedling vines crushing mechanism of the peanut pickup combine harvester.

Shape memory cyclic behavior and mechanical durability of woven fabric reinforced shape memory polymer composites

The shape memory cyclic behavior and mechanical durability of the shape memory polymer (SMP) and three woven fabrics (plain, twill, and satin weaves) reinforced shape memory polymer composite (WFR-SMPCs) are characterized to investigate the effect of woven textures on the mechanical and shape memory properties of WFR-SMPCs. Shape memory cycle test, shape memory durability test, and microscopic observation for SMP and WFR-SMPCs were carried out. Experimental results show that the SMP is temperature-sensitive, and higher temperature facilitates the shape memory performance of the material. The woven fabric reinforcements can significantly enhance the mechanical properties of the SMP matrix while still maintaining good shape recovery ratios above 98 % and shape fixation ratios above 90 % even though there is a slight decrease in these values. The twill WFR-SMPC displays the best mechanical performance. The satin WFR-SMPC has the highest shape recovery ratio. The twill WFR-SMPC performs the best in load-bearing capacity and recovery stress. The microscopic observations show that the rotational misalignment and bending of the fiber tows, and damage to the matrix are the main failure modes of the WFR-SMPCs at high shear strain.

Probing fretting wear behavior of gauge-changeable spline axle under rotational bending loads

The latest generation of gauge-changeable trains in China feature designs with their wheels and axles connected by spline couples and cylindrical fits. In comparison to the interference fitted wheelset, the spline axle with clearance fit is more prone to fretting damage. In this study, the stress distribution of spline axle was analyzed using finite element method. Then, a rotatory bending test on scaled wheel/axle samples was conducted to reveal the fretting wear behavior of the gauge-changeable axle. During traction, the contact stress of the spline peaks at 311 MPa on the tooth’s root side, with a corresponding relative slip of 14 μm. Fretting wear is observed in the spline axle, the damage zone of the wheel seat can be categorized into five bands (A–E), and severely damaged areas are covered with red-brown debris. Moreover, the main damage mechanism of untreated spline axle and surface-modified spline axle is delamination accompanied with oxidation. The improved properties of plasma nitriding and grease lubricant are attributed to the high surface hardness and residual compressive stress, as well as low frictional stress.

Impact of biological environment on bending fatigue lifetime in additive-manufactured polylactic acid fabricated by 3D-printing

Polylactic acid (PLA) has become desirable for biomedical applications, particularly implantable devices. However, the degradation of PLA in biological environments under mechanical stress remains incompletely understood and requires further investigation. This study compared the plain fatigue (PF) and the biodegraded fatigue (BDF) behavior of 3D-printed PLA. For this purpose, two sets of standard fatigue specimens were additively manufactured by the fused filament fabrication (FFF) method. One set was used for plain fatigue testing, and the other was immersed for 330 days in simulated body fluid (SBF). After immersion, the samples were dried and weighed before fatigue testing. The fully reversed rotary bending fatigue tests were conducted on both sets of specimens, and the stress-lifetime (S-N) curves were obtained. Additionally, the fatigue properties of PF and BDF specimens were evaluated. Moreover, the fracture behaviors of the materials were studied using field emission scanning electron microscopy (FESEM). The outcomes implied that the weight of the samples extended during the immersion period, primarily due to water absorption by the PLA. However, after drying, the final weights did not change compared to the weights before immersion. The SBF immersion significantly reduced the fatigue performance of the biodegraded samples comparing the PF result.

Enhancing Fatigue Resistance of Polylactic Acid through Natural Reinforcement in Material Extrusion.

This research paper aims to enhance the fatigue resistance of polylactic acid (PLA) in Material Extrusion (ME) by incorporating natural reinforcement, focusing on rotational bending fatigue. The study investigates the fatigue behavior of PLA in ME, using various natural fibers such as cellulose, coffee, and flax as potential reinforcements. It explores the optimization of printing parameters to address challenges like warping and shrinkage, which can affect dimensional accuracy and fatigue performance, particularly under the rotational bending conditions analyzed. Cellulose emerges as the most promising natural fiber reinforcement for PLA in ME, exhibiting superior resistance to warping and shrinkage. It also demonstrates minimal geometrical deviations, enabling the production of components with tighter dimensional tolerances. Additionally, the study highlights the significant influence of natural fiber reinforcement on the dimensional deviations and rotational fatigue behavior of printed components. The fatigue resistance of PLA was significantly improved with natural fiber reinforcements. Specifically, PLA reinforced with cellulose showed an increase in fatigue life, achieving up to 13.7 MPa stress at 70,000 cycles compared to unreinforced PLA. PLA with coffee and flax fibers also demonstrated enhanced performance, with stress values reaching 13.6 MPa and 13.5 MPa, respectively, at similar cycle counts. These results suggest that natural fiber reinforcements can effectively improve the fatigue resistance and dimensional stability of PLA components produced by ME. This paper contributes to the advancement of additive manufacturing by introducing natural fiber reinforcement as a sustainable solution to enhance PLA performance under rotational bending fatigue conditions. It offers insights into the comparative effectiveness of natural fibers and synthetic counterparts, particularly emphasizing the superior performance of cellulose.

Biomechanical Effects of Titanium Alloy Based Single versus Dual Cage Fusion Devices

Degenerative disc disease is an increasing problematic complication following lumbar fusion surgeries. Posterior lumbar interbody fusion (PLIF) is a well-established surgical method for spine stability following intervertebral disc removal. The position and number of titanium cages in PLIF are remain contingent on individual surgeon experience. Thus, a systemic investigation of the efficacy of titanium single mega cage versus two cages in treating degenerative lumbar spinal diseases is imperative. A biomechanical study was aimed to compare the stability achieved in PLIF through interbody reconstruction using a single mega cage (32 mm) Vs. a dual cage (22 mm). Normal intact finite element model of L3–L4 was developed based on computed tomography images from a healthy 27-year-old male volunteer. The study tested the intact model (Model A) and its surgically operated counterparts using four PLIF implantation methods: single transverse cage (Model B), single transverse cage with bone graft (Model C), dual transverse cage (Model D), and dual transverse cage with bone graft (Model E). Combined loads simulating physiological motions—flexion, extension, axial rotation, and lateral bending —were applied across all loading directions. The assessment includes all model range of motion (ROM), micromotion between the cage and endplate, and stress on the cage and internal fixation system (screw and rod). The ROM between Models B, C, D and E were consistently reduced by over 71% compared to intact Model A under all motion scenarios. Model D exhibited the highest peak stress of 115 MPa on the cage during flexion, surpassing Model C and E (Flexion) by fourfold. Model E demonstrated the lowest cage stress (20 MPa) during extension, outperforming the other models. Notably, Model E exhibited minimal endplate stress (2 MPa), cage stress (21 MPa), micromotion (13 µm) during extension, and screw-rod stress (56 MPa) during flexion, making it superior to other implantation methods. In the context of PLIF, Model E showed enhanced biomechanical stability, reducing ROM, stress on the endplates, cage, screw-rod system and micromotion. Alternatively, Model C may be a viable alternative in standard PLIF, especially in cases with limited intervertebral space, providing efficient clinical outcomes with shorter operative times and reduced costs and ease of implantation. Also, this computational study provides valuable understandings into optimizing cage implantation strategies for improved outcomes during PLIF.

An analytical model for predicting residual stress in shot peening with strain energy method

In this study a model by novel analytical approach is developed and experimentally verified for shot peening residual stress distribution. The residual stress field induced by single shot impact is calculated by using Glinka–Molski energy-based method and kinematic hardening model. The formulation of the compressive residual stress (CRS) distribution is often based on plane strain or plane stress. It can be determined from the derived relation presented in this paper, the final residual stress in the full coverage conditions is the average of the two strain and stress plane expressions proposed by previous researchers. The distribution of residual stress is one of the key differences between the profiles produced by the results of the current model. There is a significant distinction between surface residual stress and maximum CRS, because the CRS profile near the surface is more curved compared to profiles obtained in earlier analytical models. The experimental data obtained by XRD analysis indicate the correctness and precision of the current model. Another goal of this study is to increase the fatigue life of GTD-450 stainless steel by shot peening at two different peening intensities. The fatigue life of samples were obtained by rotary bending test. Analytical results that confirmed by experimental findings shown bigger maximum compressive residual stresses occurred in higher shot peening intensities. This incident can improved fatigue life by deeper plastically deformed layer.

Crossing the Cervicothoracic Junction: A Biomechanical Investigation of C7 vs T1 Caudal Selection's Effect on Adjacent Segment Motion in Posterior Cervical Fusion.

Biomechanical Study. This study aims to evaluate the biomechanical adjacent segment effects of multi-level posterior cervical fusion constructs that terminate at C7 compared to those that terminate at T1 in cadaveric specimens. The cervicothoracic junction poses unique challenges for spine surgeons. Deciding to terminate multi-level posterior cervical fusion constructs at C7 or extend them across the cervicothoracic junction remains a controversial issue. Six cadaveric specimens underwent biomechanical testing in the intact state and after instrumentation with constructs from C3 and terminating at either C7 or T1. Range of motion (ROM) was assessed in flexion-extension, lateral bending, and axial rotation globally and at cranial and caudal adjacent segments. There was a significant decrease in overall flexion/extension by both C7 (-35.5°, P=0.002) and T1 (-39.8°, P=0.002) instrumentation compared to the intact spine. T1 instrumentation had significantly lower (-4.3°, P=0.008) flexion/extension ROM compared to C7 instrumentation. There were significant decreases in axial rotation by both C7 (-31.4°, P=0.009) and T1 (-36.8°, P=0.009) instrumentation compared to the intact spine, but no significant differences were observed between the two. There were also significant decreases in lateral bending by both C7 (-27.9°, P=0.022) and T1 (-33.7°, P=0.022) instrumentation compared to the intact spine, but no significant differences were observed between the two. No significant differences were observed in ROM at cranial or caudal adjacent segments between constructs terminating at C7 and those extending to T1. This biomechanical investigation demonstrates that constructs that cross the cervicothoracic junction experience less overall spinal motion in flexion-extension compared to those that terminate at C7. However, contrary to prior studies there is no difference in cranial and caudal adjacent segment motion. Surgeons should make clinical decisions regarding the caudal extent of fusion in multi-level posterior cervical fusions without major concerns about adjacent segment motion.

Study of cracks in the last-stage rotor blade of a steam turbine and the corrosion fatigue properties of its materials

In this study, to clarify the failure mechanism of the last-stage rotor blade in the low-pressure cylinder of a steam turbine, the peculiarities of crack initiation and propagation on the inlet side of the last-stage rotor blade at a distance of 125–165 mm were analyzed, along with the corrosion fatigue properties of its materials. The results showed that crack initiation occurred at the tip of the pit due to a combination of factors: stress concentration at the tip of the pit, corrosion of the Cr-poor area near the prior austenite grain boundary, centrifugal tensile stress, and steam bending stress. The crack propagation could be divided into the initial intergranular and late transgranular propagation stages. The main reason for the initial intergranular propagation was stress corrosion, and the main reason for the later transgranular propagation was corrosion fatigue. High-frequency induction quenching technology can improve the microhardness of the blade's surface material and enhance the blade's resistance to water erosion, but it may also reduce the corrosion fatigue resistance of the blade material. The rotary bending corrosion fatigue test can effectively simulate the crack propagation process of the blade. These results are of great significance for the safe operation of the last-stage rotor blade in the low-pressure cylinder of a steam turbine.