Axial Stability Research Articles

Study on the dynamic mechanical properties of winding‐block axial structure considering short circuit strain rate effect

AbstractTransformers may suffer multiple short‐circuit impacts during long‐term operation, and axial instability is one of the typical types of serious accidents caused by short‐circuit faults. The axial instability form of the winding‐block structure is analysed, and the dynamic solution of the winding short‐circuit electromagnetic force is obtained by establishing the three‐dimensional magnetic‐circuit‐force multi‐physical field coupling simulation model. The influence of strain rate on the cushion block constitutive equation is corrected, and the modified model is verified by short‐circuit impact test and quasi‐static test. The research results show that for 110 kV 31.5 MVA transformers, the maximum electromagnetic axial resultant force of winding is 363.16 kN, and the ultimate tilt force is 1214.2 kN. The pre‐tightening force configuration is accordingly recommended to range from 363.16 to 608.28 kN, which is narrowed by 18.49% compared with the static calculation method; Meanwhile, adding a logarithmic strain rate correction term to the classical constitutive equation of the cushion block can achieve a good correction of the stress‐strain relationship with the coefficient of determination above 0.99, and the cushion block has a larger elastic modulus under high strain rate load. The research results provide an important theoretical reference for the axial stability structure of transformers.

Wedge osteotomy combined with internal fixation in the treatment of Mayo IIB olecranon fractures.

This study aimed to biomechanically compare the maximum rotational, axial movements, and compression forces between fracture fragments before and after 1-4 mm fracture site resorption among interlocking nails, compression nails, and newly designed compressive anti-resorption (CARES) nails compressed with tube and coil spring. We determined the maximum axial/rotational movements and interfragmentary compression loads between fragments on 10 interlocking nails, 10 compression nails, and 10 CARES nails with 30 composite femurs. Using a compression-distraction testing device, 6 N·m external and internal torques were applied, and we evaluated the maximum rotational and axial displacement between fragments after 1-4 mm fracture site resorption. When 6 N·m of internal-external rotation torque was applied after 2 mm fracture site resorption, the maximum rotational displacement between fragments in the CARES nail was 3 ± 0.52 mm, 101% less than the 6.03 ± 0.83 value in the compression nail and 100% less than the 6 ± 1 mm value measured in the interlocking nail (P=.000). The compression between fragments was 298 ± 72 N in the CARES nail after 1 mm of resorption, while this value was measured as 0 in the other nails. There was a significant difference in rotational, axial stability, and interfragment compression among the different femoral nails after 1-4 mm fracture site resorption. The CARES nail having additional coil springs seems significantly biomechanically superior to compression nails and interlocking nails, providing maximum rotational, axial stability, and interfragment compression after fracture site resorption.

Composite Biosynthetic Graft for Repair of Long-Segment Tracheal Stenosis: A Pilot In Vivo and In Vitro Feasibility Study.

Pediatric patients who undergo surgery for long-segment congenital tracheal stenosis (LSCTS) have suboptimal outcomes and postsurgical complications. To address this, we propose a biosynthetic graft comprising (1) a porcine small intestinal submucosa extracellular matrix (SIS-ECM) patch for tracheal repair, and (2) a resorbable polymeric exostent for biomechanical support. The SIS-ECM patch was evaluated in vivo in an ovine trachea model over an 8 month period. Concurrently, the biosynthetic graft was evaluated in a benchtop lamb trachea model for biomechanical stability. In vivo results show that SIS-ECM performs better than bovine pericardium (control) by preventing granulation tissue/restenosis, restoring tracheal architecture, blood vessels, matrix components, pseudostratified columnar and stratified epithelium, ciliary structures, mucin production, and goblet cells. In vitro tests show that the biosynthetic graft can provide the desired axial and flexural stability, and biomechanical function approaching that of native trachea. These results encourage future studies to evaluate safety and efficacy, including biomechanics and collapse risk, biodegradation, and in vivo response enabling a stable long-term tracheal repair option for pediatric patients with LSCTS and other tracheal defects.

Comparison of double chevron-cut and biplanar distal femoral osteotomy techniques: A biomechanical study.

This study aimed to compare the stability and mechanical properties of the double chevron-cut (DCC) and biplanar (BP) distal femoral osteotomy (DFO) techniques, along with analyzing their respective contact surface areas. Biomechanical testing was performed using sawbone and 3D modeling techniques to assess axial and torsional stability, torsional stiffness, and maximum torque of both osteotomy configurations. Additionally, 3D models of the sawbone femur were created to calculate and compare the contact surface area of the DCC, BP, and conventional single-plane DFO techniques. Axial stiffness and maximum strength did not significantly differ between the two osteotomy techniques. However, in terms of torsional properties, the DCC technique exhibited superior torsional stiffness compared to the BP group (27 ± 7.7 Nm/° vs. 4.5 ± 1.5 Nm/°, p = 0.008). Although the difference in maximum torque did not reach statistical significance (63 ± 10.6 vs. 56 ± 12.1, p = 0.87), it is noteworthy that the DCC group sawbone model exhibited fracture in the shaft region instead of at the osteotomy site. Therefore, the actual maximum torque of the DCC construct may not be accurately reflected by the numerical values obtained in this study. The contact surface area analysis revealed that the BP configuration had the largest contact surface area, 111% larger than that of the single-plane configuration. but 60% of it relied on the less reliable axial cut. Conversely, the DCC osteotomy offered a 31% larger contact surface area than the single-plane configuration, with both surfaces being weight-bearing. The DCC osteotomy exhibited superior mechanical stability, showing improved rotational stiffness and maximum torque when compared to the BP osteotomy. Although the BP osteotomy resulted in a larger contact surface area than the DCC osteotomy, both were larger than the conventional single-plane configuration. In clinical practice, both the DCC and BP techniques should be evaluated based on patient-specific characteristics and surgical goals.

Treatment of femoral bone loss in revision total hip arthroplasty: a clinical practice review.

Patient and implant selection is essential to optimize outcome. Femoral bone loss classifications such as the American Academy of Orthopaedic Surgeons, Gross, and Paprosky classifications permit surgeons to systematically manage bone stock deficiencies and guide implant selection. Here we provide a comprehensive report on the pitfalls and management of this reconstructive challenge. Preoperative planning remains vital to the treatment of femoral bone loss in revision hip arthroplasty and the authors believe it is essential and should include the entire femur. This commonly includes imaging for bone loss such as Judet views or computed tomography scan and must include the entire femur though additional radiographs such as Judet views apply more for acetabular bone loss as opposed to femoral bone loss. All patients should have pre-operative work up to exclude infection. If any of these results area elevated, an aspirate and sampling is required to guide microbiological management. Classically with regards femoral revision surgery, uncemented fixation has proven to give the best outcomes but surgeons must remain flexible and use cemented fixation when necessary. Adequate proximal bone stock permits the use of implants used in primary joint surgery. Implants with proximal modularity can be used in cases where bone stock allows for superb proximal bone support. The vast majority of femoral revisions have inadequate proximal bone stock, thus distally fixed stems should be used and have been shown to provide both axial and rotational stability provided there is an intact isthmus. Taper fluted stems can provide good outcomes even in cases of major bone loss. However, with severe bony loss, impaction grating or the use of a megaprotsthesis is sometimes necessary and is down to surgeon choice and preference. This article has been written as a guide for management and summarises the best evidence available.

Research on the Axial Stability of Large-Capacity Magnetic Levitation Flywheel Driven by Axial-Flux Permanent Magnet Machine Based on Runge-Kutta Method

Research on the Axial Stability of Large-Capacity Magnetic Levitation Flywheel Driven by Axial-Flux Permanent Magnet Machine Based on Runge-Kutta Method

Axial electrodynamic suspension in a Hybrid bearingless motor with active and passive axial stabilization

Axial electrodynamic suspension in a Hybrid bearingless motor with active and passive axial stabilization

Research on the Influence of Compression and Offset of Cushion Blocks on the Axial Strength of Transformers

The instability of the winding-cushion structure is one of the primary causes of transformer failures. Insulation cushion compression and offset are the predominant forms leading to structural instability. Therefore, this paper, using the SFSZ7-31500/110 transformer as an example, first derives the theoretical formula for mechanical stress calculation. It clarifies the key influencing parameters of the winding-cushion block structure on the axial bending stress of the winding. Subsequently, an electromagnetic force finite element calculation model is established to obtain the axial force distribution in the winding and the distribution of unbalanced displacement during short-circuit processes. Based on the force and offset distribution, a specific cushion block compression and offset test platform is constructed. By setting different cushion block variables, the effects of cushion block unbalanced height and cushion block offset on the winding’s bending elastic modulus are determined. Finally, a simulation model for stress calculation of the winding-cushion block structure is established, revealing the influence pattern of cushion block compression and offset instability on the axial strength of the winding. The results of this study indicate that the greater the uneven cushion block height, the lower the axial strength of the winding. Under the same cushion block offset angle, winding structures with non-uniform cushion block offsets exhibit the worst axial stability. When the offset angles are 30°, 45°, and 60°, the maximum axial bending stress of the winding increases by 1.73%, 3.46%, and 7.82%, respectively. Increasing the offset angle exacerbates the decrease in the axial strength of the winding up to a certain extent. The findings in this study have significant implications for enhancing a transformer’s short-circuit resistance.

The Effect of Cerclage Banding Distally to a Clamshell Fracture Pattern in Total Hip Arthroplasty-A Biomechanical Study.

As currently there is no existing biomechanical work on the topic of interest, the aim of the current study was to investigate the effect of cerclage banding distally to an intraoperatively occurring proximal periprosthetic femoral clamshell fracture versus a non-fractured femur after total hip arthroplasty. A diaphyseal anchoring stem was implanted in twenty paired human cadaveric femora, assigned to a treatment and a control group. In the treatment group, each specimen was fitted with a cerclage band placed 3 mm distally to a clamshell fracture, created with an extent of 40% of the anchoring length of the stem. The resulting fragment was not treated further. The contralateral specimens were left with the stems without further fracture creation or treatment. All constructs were tested under progressively increasing cyclic axial loading until failure. Relative bone-implant movements were monitored by motion tracking. Number of cycles and the corresponding load at stem loosening, defined as 1 mm displacement of the stem along the shaft axis, were 31,417 ± 8870 and 3641.7 ± 887 N in the control group, and 26,944 ± 11,706 and 3194.4 ± 1170.6 N in the treatment group, respectively, with no significant differences between them, p = 0.106. From a biomechanical perspective, cerclage banding distally to an intraoperative clamshell fracture with an extent of 40% of the anchoring length of the stem demonstrated comparable resistance against hip stem loosening versus a non-fractured femur. It may therefore represent a valid treatment option to restore the full axial stability of a diaphyseal anchoring stem. In addition, it may be considered to keep the medial wall fragment unfixed, thus saving operative time and minimizing associated risks.

Intramedullary implant stability affects patterns of fracture healing in mice with morphologically different bone phenotypes

Almost all prior mouse fracture healing models have used needles or K-wires for fixation, unwittingly providing inadequate mechanical stability during the healing process. Our contention is that the reported outcomes have predominantly reflected this instability, rather than the impact of diverse biological conditions, pharmacologic interventions, exogenous growth factors, or genetic considerations. This important issue becomes obvious upon a critical review of the literature. Therefore, the primary aim of this study was to demonstrate the significance of mouse-specific implants designed to provide both axial and torsional stability (Screw and IM Nail) compared to conventional pins (Needle and K-wires), even when used in mice with differently sized marrow canals and diverse genetic backgrounds. B6 (large medullary canal), DBA, and C3H (smaller medullary canals) mice were employed, all of which have different bone morphologies. Closed femoral fractures were created and stabilized with intramedullary implants that provide different mechanical conditions during the healing process. The most important finding of this study was that appropriately designed mouse-specific implants, providing both axial and torsional stability, had the greatest influence on bone healing outcomes regardless of the different bone morphologies encountered. For instance, unstable implants in the B6 strain (largest medullary canal) resulted in significantly greater callus, with a fracture region mainly comprising trabecular bone along with the presence of cartilage 28 days after surgery. The DBA and C3H strains (with smaller medullary canals) instead formed significantly less callus, and only had a small amount of intracortical trabeculation remaining. Moreover, with more stable fracture fixation a higher BV/TV was observed and cortices were largely restored to their original dimensions and structure, indicating an accelerated healing and remodeling process. These observations reveal that the diaphyseal cortical thickness, influenced by the genetic background of each strain, played a pivotal role in determining the amount of bone formation in response to the fracture. These findings are highly important, indicating the rate and type of tissue formed is a direct result of mechanical instability, and this most likely would mask the true contribution of the tested genes, genetic backgrounds, or various therapeutic agents administered during the bone healing process.

BORS/BJR TRAVELLING FELLOWSHIP ABSTRACT: THE EFFECT OF INCREASING BONE LOSS ON THE PRIMARY STABILITY OF METAPHYSEAL SLEEVES IN THE PROXIMAL TIBIA. AN EXPERIMENTAL STUDY USING SAWBONE TIBIAS

AbstractApproximately 20% of primary and revision Total Knee Arthroplasty (TKA) patients require multiple revisions, which are associated with poor survivorship, with worsening outcomes for subsequent revisions. For revision surgery, either endoprosthetic replacements or metaphyseal sleeves can be used for the repair, however, in cases of severe defects that are deemed “too severe” for reconstruction, endoprosthetic replacement of the affected area is recommended. However, endoprosthetic replacements have been associated with high complication rates (high incidence rates of prosthetic joint infection), while metaphyseal sleeves have a more acceptable complication profile and are therefore preferred. Despite this, no guidance exists as to the maximal limit of bone loss, which is acceptable for the use of metaphyseal sleeves to ensure sufficient axial and rotational stability. Therefore, this study assessed the effect of increasing bone loss on the primary stability of the metaphyseal sleeve in the proximal tibia to determine the maximal bone loss that retains axial and rotational stability comparable to a no defect control.Methodsto determine the pattern of bone loss and the average defect size that corresponds to the clinically defined defect sizes of small, medium and large defects, a series of pre-operative x-rays of patients with who underwent revision TKA were retrospectively analysed. Ten tibiae sawbones were used for the experiment. To prepare the bones, the joint surface was resected the typical resection depth required during a primary TKA (10mm). Each tibia was secured distally in a metal pot with perpendicular screws to ensure rotational and axial fixation to the testing machine. Based on X-ray findings, a fine guide wire was placed 5mm below the cut joint surface in the most medial region of the plateau. Core drills (15mm, 25mm and 35mm) corresponding to small, medium and large defects were passed over the guide wire allowing to act at the centre point, before the bone defect was created. The test was carried out on a control specimen with no defect, and subsequently on a Sawbone with a small, medium or large defect. Sleeves were inserted using the published operative technique, by trained individual using standard instruments supplied by the manufacturers. Standard axial pull-out (0 – 10mm) force and torque (0 – 30°) tests were carried out, recording the force (N) vs. displacement (mm) curves.ResultsA circular defect pattern was identified across all defects, with the centre of the defect located 5mm below the medial tibial base plate, and as medial as possible. Unlike with large defects, small and medium sized defects reduced the pull-out force and torque at the bone-implant interface, however, these reductions were not statistically significant when compared to no bony defect.ConclusionsThis experimental study demonstrated that up to 35mm radial defects may be an acceptable “critical limit” for bone loss below which metaphyseal sleeve use may still be appropriate. Further clinical assessment may help to confirm the findings of this experimental study. This study is the first in the literature to aim to quantify “critical bone loss” limit in the tibia for revision knee arthroplasty.Declaration of Interest(a) fully declare any financial or other potential conflict of interest

Effect of wire mesh casing treatment on axial compressor performance and stability

In this paper, a kind of Wire Mesh Casing Treatment (WMCT) is proposed to improve the stable operating range of the compressor. In contrast to the traditional circumferential groove, as for WMCT, a layer of wire mesh is laid on the surface of the circumferential groove. Parametric studies were conducted on the low-speed axial flow compressor, including the groove width, axial location, and mesh count. The optimum axial location for WMCT is related to its groove width. A higher wire mesh count results in a smaller compressor stall margin improvement. Steady simulations were carried out to study the effect of WMCT on the flow structure of the compressor. The wire mesh in the WMCT has a certain flow resistance, which restricts the flow into and out of the groove. Due to the WMCT, the flow parameter in the tip region of the rotor is less sensitive to changes in the operating conditions of the compressor. The WMCT causes the rotor tip blade loading to shift backward, inhibiting the formation of spill forward of the leakage flow, and thus improving the stability of the compressor. The flow resistance on the groove surface is a new degree-of-freedom for the casing treatment designer.

Additional Plate Fixation of Hinge Fractures After Varisation Distal Femoral Osteotomies Provides Favorable Torsional Stability: A Biomechanical Study

Background: Hinge fractures are considered risk factors for delayed or nonunion of the osteotomy gap in distal femoral osteotomies (DFOs). Limited evidence exists regarding the treatment of hinge fractures after DFO, which could improve stability and thus bone healing. Purpose: To (1) examine the effect of hinge fractures on the biomechanical properties of the bone-implant construct, (2) evaluate the biomechanical advantages of an additional fixation of a hinge fracture, and (3) test the biomechanical properties of different types of varisation DFOs. Study Design: Controlled laboratory study. Methods: A total of 32 fresh-frozen human distal femora equally underwent medial closing wedge DFO or lateral opening wedge DFO using a unilateral locking compression plate. The following conditions were serially tested: (1) preserved hinge; (2) hinge fracture along the osteotomy plane; (3) screw fixation of the hinge fracture; and (4) locking T-plate fixation of the hinge fracture. Using a servo-hydraulic materials testing machine, we subjected each construct to 15 cycles of axial compression (400 N; 20 N/s) and internal and external rotational loads (10 N·m; 0.5 N·m/s) to evaluate the stiffness. The axial and torsional hinge displacement was recorded using a 3-dimensional optical measuring system. Repeated-measures 1-way analysis of variance and post hoc Bonferroni correction were used for multiple comparisons. Statistical significance was set at P < .05. Results: Independent from the type of osteotomy, a fractured hinge significantly (P < .001) increased rotational displacement and reduced stiffness of the bone-implant construct, resulting in ≥1.92 mm increased displacement and ≥70% reduced stiffness in each rotational direction, while the axial stiffness remained unchanged. For both procedures, neither a screw nor a plate could restore intact rotational stiffness (P < .01), while only the plate was able to restore intact rotational displacement. However, the plate always performed better compared with the screw, with significantly higher and lower values for stiffness (+38% to +53%; P < .05) and displacement (–55% to −72%; P < .01), respectively, in ≥1 rotational direction. At the same time, the type of osteotomy did not significantly affect axial and torsional stability. Conclusion: Hinge fractures after medial closing wedge DFO and lateral opening wedge DFO caused decreased bone-implant construct rotational stiffness and increased fracture-site displacement. In contrast, the axial stiffness remained unchanged in the cadaveric model. Clinical Relevance: When considering an osteosynthesis of a hinge fracture in a DFO, an additional plate fixation was the construct with the highest stiffness and least displacement, which could restore intact hinge rotational displacement.

Multi-objective ant lion optimization for parameter optimization of wireless power transfer systems

The effective transmission distance of a magnetic coupling resonance (MCR) wireless power transfer (WPT) system is an essential index of wireless power transfer. Existing systems often suffer from short transmission distances, low power, and low efficiency. In this paper, a method is proposed for improving the parameters of wireless power transfer systems to enhance the performance of the systems. The main parameters affecting the output power and transmission efficiency are determined by analyzing the MCR WPT system with SS-type topology. In addition, the multi-objective ant lion optimizer is combined with tent chaotic mapping to generate the location information of the initial population by using the distribution and randomness of tent chaotic mapping, which increases the diversity of the people and improves the convergence speed and global search capability of the algorithm to achieve multi-objective parameter optimization, and the optimized model is also analyzed. Experiments show that the optimized MCR WPT system has improved output power and transmission efficiency at a longer distance. The optimal transmission distance of the system is about 0.2 m with a maximum output power of 129.3 W, and the axial offset stability of the system is enhanced. Finally, the effectiveness of the improved model is verified by building a prototype system. It provides a valuable reference for the research of improving wireless power transfer.

Influence of a Capsular Tension Ring on Capsular Bag Behavior of a Plate Haptic Intraocular Lens: An Intraindividual Randomized Trial

PurposeTo evaluate the influence of a capsular tension ring (CTR) on rotational stability, decentration, tilt and axial stability of a 11.0mm plate haptic intraocular lens (IOL) DesignIntraindividual, randomized, double masked, controlled, clinical trial. ParticipantsPatients scheduled for sequential same day bilateral cataract surgery. MethodsAll patients were randomized to receive a CTR and a plate haptic IOL in one eye and a plate haptic IOL in the fellow eye only. IOL axis assessment was performed at the end of surgery (EOS), 1 hour (1h), 1 week (1w), 1 month (1m) and 6 months (6m) using a high precision evaluation method. Decentration and tilt of the crystalline and pseudophakic lenses were assessed preoperatively, at 1w and 6m using an anterior segment OCT (AS-OCT). Main outcome measuresRotational stability from EOS to 6m and at all follow up visits. Decentration and tilt at 6m. Differences in axial shift between 1w and 6m. ResultsOne hundred and thirty eyes of 65 patients were included in the study. Absolute rotation from EOS to 6m was 2.8°±3.9° and 3.2°±5.3° for the CTR and control groups, respectively (p=0.613). IOL decentration and IOL tilt at 6m were 0.29±0.1mm and 0.24±0.1mm and 6.7°±2.8° and 5.6°±1.6° for the CTR and control groups, respectively (p=0.058, p<0.01). A posterior IOL shift of 0.31±0.31 mm and 0.19±0.14 mm was observed in the CTR and control groups, respectively. ConclusionsConcomitant implantation of a CTR and a plate haptic IOL did not improve the overall rotational stability of the IOL compared to the control group. A negative effect of the CTR on decentration, tilt and axial stability was observed. The simultaneous use of a CTR and a plate haptic IOL in the absence of zonular weakness at the time of cataract surgery should be considered with caution.

Numerical investigation of mixing process of high-pressure jet-cutting clay by water–air coaxial nozzle considering soil rheological properties

Simulation and accurate modeling of the mixing process of the high-pressure jet-cutting clay by the water–air coaxial nozzle is significantly important for the performance optimization of the triple fluid jet grouting. In this paper, a numerical model considering the soil rheological properties is proposed to investigate the mixing process of the high-pressure jet-cutting clay. The cohesive force model of clay is obtained based on the solution of the power law index and consistency factor by coupling the Herschel-Bulkley and soil logarithmic models. The interaction model among the gas phase, the liquid phase, and the clay medium is further established through use of the drag force model. A laboratory device of high-pressure jet-cutting transparent clay is developed to prove the feasibility of the proposed model for the mixing process of the high-pressure jet-cutting clay. Finally, using the validated numerical model, the mixing process of the high-pressure jet-cutting clay by the water–air coaxial nozzle with varying radial spacings between the air nozzle and water nozzle is numerically investigated, and the axial stability of the jet, the width of the cross-sectional profile, and the variation of the central axis velocity field of the mixing process are analyzed. Results demonstrated that the variation trend of the jet in both simulations and experiments is consistent, and the maximum error in jet depth is better than 3.3%, validating the accuracy of the numerical model of the mixing process of the high-pressure jet-cutting clay. The optimal radial spacing size for a water–air coaxial nozzle in high-pressure jetting of clay medium is 1.4 mm, which provides the best axial stability, the narrower jet cross-section, and the slowest decay of jet velocity along the central axis.

A peak time shifting phenomenon in transformer axial short‐circuit electromagnetic force due to the coupling of electromagnetic‐axial vibration

AbstractAccurately calculating axial electromagnetic force is essential to analyse transformer winding axial stability. Prior research has mainly focused on the effect of winding structure on static axial electromagnetic force and studying vibration by substituting the static force in a time‐varying function. However, the coupling effect between axial electromagnetic force and winding vibration has not been addressed, and no calculation method for the axial electromagnetic force that considers both winding meso‐structures and vibration coupling effects has been proposed. Previously the authors presented an electromagnetic force calculation model that considers winding structure characteristics, and an iterative algorithm for magnetic‐structure coupling calculation. Currently, the winding vibration model was first proposed and the dynamic calculation method was formulated. By applying the method to a typical 110kV transformer, the spatial‐temporal distribution of winding axial short‐circuit electromagnetic force was obtained. It was found that the peak value of the axial short‐circuit electromagnetic force of some windings appears at the second or third peak moment of the short‐circuit current, which is called as peak time shift phenomenon. Further stress analysis indicates that existing evaluation methods may overestimate the short‐circuit resistance of windings by only considering short‐circuit electromagnetic force under maximum peak of short‐circuit current.

Axial compression stability of corroded circular steel tubes in simulated seawater environments

To investigate the influence of seawater corrosion damage on the axial compression stability of circular steel tubes, this study proposes a novel method (hereinafter referred to as the ‘thickness equivalent method’) for calculating the equivalent wall thickness based on the yield load determined through material property tests. To this end, a formula for calculating the equivalent regularised slenderness ratio of corroded circular steel tubes is derived. Subsequently, corrosion, material property and axial compression tests are conducted using circular steel tubes with different sectional dimensions, and numerical models are developed. The numerically obtained load–lateral displacement and load–strain curves are in good agreement with the test curves, validating the accuracy of the numerical models. Finally, a parameter study is conducted using the validated numerical models. To facilitate the examination of corroded circular steel tubes, a novel formula, representing a continuous function of the regularised slenderness ratio as opposed to the previous piecewise function, for computing the stability coefficient is derived. The test results demonstrate that the proposed method accurately predicts the ultimate axial compression bearing capacity of corroded circular steel tubes. Furthermore, based on the theoretical derivation, the relationship between the axial compression ultimate bearing capacity and the corrosion ratio for ϕ48 × 3 and ϕ57 × 3.5 steel tubes, considering various equivalent regularised slenderness ratios, is established.

Parameter sensitivity analysis of the axial stability for a marine flexible pipe

Marine unbonded flexible pipes serve as the most essential equipment in offshore oil and gas exploration and exploitation. Axial compressive loads during installation or in service in the complex marine environment usually lead to buckling failure. A flexible pipe is a composite structure with multiple functional layers, of which the tensile armor layer plays a key role with regard to the response of the pipe subjected to axial loads. In this paper, a simplified three-dimensional finite element model is developed, focusing on the tensile layer and replacing the carcass layer, pressure sheath layer, and pressure armor layer by a cylindrical rigid body to reduce computational expense. By using this model, the buckling failure modes of the tensile armor layer (in particular the birdcaging phenomenon) are analyzed. Several key parameters that affect the stability of the flexible pipe under axial compression and torsion are emphasized, and their effects on its axial and torsional stiffness are compared and discussed. The results show that both the lay angle of the steel wires and the interlayer friction coefficient have a significant influence on the axial and torsional stiffness of the pipe, whereas the damaged length of the outer sheath has virtually no effect.

Medial helical versus straight lateral plating of distal femoral fractures—a biomechanical comparative study

BackgroundDistal femoral fractures are commonly treated with lateral straight plates. However, the lateral approach may not always be desirable, and 180°-helical plates may be an alternative. AimTo investigate the biomechanical competence of 180°-helical plating versus standard straight lateral plating of unstable fractures at the distal femur. MethodsTwelve left artificial femora were instrumented with a 15-hole Locking Compression Plate–Distal Femur, using either 180°-helical plates (group 1) or conventional straight lateral plates (group 2). An unstable distal femoral fracture AO/OTA 33-A3.3 was simulated. All specimens were biomechanically tested under quasi-static and progressively increasing combined cyclic axial and torsional loading in internal rotation until failure. FindingsInitial axial stiffness (N/mm) was significantly higher in group 1 (185.6 ± 50.1) compared to group 2 (56.0 ± 14.4), p < 0.001. Group 1 demonstrated significantly higher initial interfragmentary flexion (°) and significantly lower initial varus/valgus deformation (°) under 500 N static axial compression versus group 2 (2.76 ± 1.02 versus 0.87 ± 0.77 and 4.08 ± 1.49 versus 6.60 ± 0.47), p ≤ 0.005. Shear displacement (mm) under 6 Nm static torsion was significantly higher in group 1 versus group 2 in both internal (1.23 ± 0.28 versus 0.40 ± 0.42) and external (1.21 ± 0.40 versus 0.57 ± 0.33) rotation, p ≤ 0.013. Cycles to failure and failure load (N) (clinical/catastrophic) were significantly higher in group 1 (12,484 ± 2116/13,752 ± 1518 and 1748.4 ± 211.6/1875.2 ± 151.8) compared to group 2 (7853 ± 1262/9727 ± 836 and 1285.3 ± 126.2/1472.7 ± 83.6), p ≤ 0.001. InterpretationAlthough 180°-helical plating using a pre-contoured standard straight lateral plate was associated with higher shear and flexion movements, it demonstrated improved initial axial stability and resistance against varus/valgus deformation compared to straight lateral plating. Moreover, the helical plates were associated with significantly higher endurance to failure. From a biomechanical perspective, 180°-helical plating may be considered as a valuable alternative to standard straight lateral plating of unstable distal femoral fractures.