Post-buckling behavior estimation of rigidly supported cylindrical composite panels in case shear

We present the solution of the geometrically nonlinear problem of the shear-critical behavior of a thin composite cylindrical panel of small curvature of orthotropic structure. The obtained solution considers the conditions of all-round rigid support. The expression for determining the membrane stresses arising in the supercritical state is given. When considering a linear problem, expressions for determining the critical shear flow are given. A method for determining the nonlinear stress-strain state in the overcritical state for a given thickness and stacking of an orthotropic panel is presented. The obtained solutions can be used in the design of load-bearing cylindrical panels, as well as in the analysis of geometrically nonlinear behavior of defects such as delaminations.

Comparative analysis of stress-strain state of mathematical models for an individual endoprosthesis and allocomposite endoprosthesis in case of replacement of long bone defects

Background. Replacement of post-resection defects of long bones in case of a tumor process is always an urgent problem of orthopedics. Among the wide variety of materials and methods for reconstruction of post-resection defects of long bones, the most common are individual, modular arthroplasty and bioreconstructive interventions. To study the mechanical properties of the structures we have chosen, various types of post-resection femoral bone defect replacement were simulated using the finite element method. The purpose was to compare the data on stress-strain states in mathematical models “allocomposite endoprosthesis” and “individual endoprosthesis” of the proximal femur. Material and methods. Mathematical models of the femur with the formation of a post-resection proximal defect replaced by a segmental bone allograft in combination with an individual endoprosthesis have been created. The model is presented in two versions, with the formation of transverse and step-cut osteotomy. Each model was examined separately with cement and cementless attachment in the area of the endoprosthesis stem. For comparison, we chose a model with complete replacement of the proximal end of the femur with an individual endoprosthesis without bone grafting. Results. Femur step-cut osteotomy can significantly reduce the level of stress in the osteotomy area. This is due to the fact that performing the step-cut osteotomy allows the bone fragments to provide resistance to shearing movement. The use of bone cement can significantly reduce the level of stress around the stem of the endoprosthesis in both variants of femoral osteotomy (transverse and step-cut). This is due to the fact that bone cement, which has an elastic modulus at an intermediate value between titanium and bone tissue, forms a layer between them, performs a damper function, that smoothes the difference in deformation values of the metal and bone tissue, thereby reducing the level of stress in them. Arthroplasty without performing bone grafting leads to increased stresses in the bone tissue due to the presence of a rigid support on the cortical bone endoprosthesis in the diaphysis along the line of its resection. Conclusions. Performing step-cut osteotomy of the femur reduces the level of mechanical stresses in the osteotomy area by half compared to models with transverse osteotomy, which is of particular importance in the early postoperative stages. The use of bone cement for fixing the stem of the endoprosthesis can also significantly reduce the level of stress in all variants of the studied models, due to the formation of a damping layer between the metal and the bone tissue. The level of stress in models without bone grafting does not depend on the use of bone cement, but is determined by the presence of a rigid support of the endoprosthesis on the cortical bone along the line of its resection.

Sternal defect reconstruction using a double-barrel vascularized free fibula flap: a case report

Total and subtotal sternectomy oncological defects can result in large deficits in the chest wall, disrupting the biomechanics of respiration. Reviewing the current literature involving respiratory function and rib motion after sternectomy, autologous rigid reconstruction was determined to provide the optimal reconstructive option. We describe a novel technique for sternal defect reconstruction utilizing a double-barrel, longitudinally oriented, vascularized free fibula flap associated with rib titanium plates fixation. Our reconstructive approach was able to deliver a physiological reconstruction, providing rigid support and protection while allowing articulation with adjacent ribs and preservation of chest wall mechanics.

Designing of Thin Composite Panels with the Post-Buckling Behavior Considering Rigid Support and Loading with Shear Flows

Geometrically non-linear problem of orthotropic thin rectangular panel post-buckling behavior with shear is solved. Deflection function takes all-boundary rigid support conditions into account. Based on derived solution method of smooth panels design which can be used for aircraft structures rib and spar webs optimal parameters is suggested.

A Semi-active Exoskeleton Based on EMGs Reduces Muscle Fatigue When Squatting

In dynamic manufacturing and warehousing environments, the work scene made it impossible for workers to sit, so workers suffer from muscle fatigue of the lower limb caused by standing or squatting for a long period of time. In this paper, a semi-active exoskeleton used to reduce the muscle fatigue of the lower limb was designed and evaluated. (i) Background: The advantages and disadvantages of assistive exoskeletons developed for industrial purposes were introduced. (ii) Simulation: The process of squatting was simulated in the AnyBody.7.1 software, the result showed that muscle activity of the gluteus maximus, rectus femoris, vastus medialis, vastus lateralis, vastus intermedius, and erector spinae increased with increasing of knee flexion angle. (iii) Design: The exoskeleton was designed with three working modes: rigid-support mode, elastic-support mode and follow mode. Rigid-support mode was suitable for scenes where the squatting posture is stable, while elastic-support mode was beneficial for working environments where the height of squatting varied frequently.The working environments were identified intelligently based on the EMGs of the gluteus maximus, and quadriceps, and the motor was controlled to switch the working mode between rigid-support mode and elastic-support mode. In follow mode, the exoskeleton moves freely with users without interfering with activities such as walking, ascending and descending stairs. (iv) Experiments: Three sets of experiments were conducted to evaluate the effect of exoskeleton. Experiment one was conducted to measure the surface electromyography signal (EMGs) in both condition of with and without exoskeleton, the root mean square of EMGs amplitude of soleus, vastus lateralis, vastus medialis, gastrocnemius, vastus intermedius, rectus femoris, gluteus maximus, and erector spinae were reduced by 98.5, 97.89, 80.09, 77.27, 96.73, 94.17, 70.71, and 36.32%, respectively, with the assistance of the exoskeleton. The purpose of experiment two was aimed to measure the plantar pressure with and without exoskeleton. With exoskeleton, the percentage of weight through subject's feet was reduced by 63.94, 64.52, and 65.61% respectively at 60°, 90°, and 120° of knee flexion angle, compared to the condition of without exoskeleton. Experiment three was purposed to measure the metabolic cost at a speed of 4 and 5 km/h with and without exoskeleton. Experiment results showed that the average additional metabolic cost introduced by exoskeleton was 2.525 and 2.85%. It indicated that the exoskeleton would not interfere with the movement of the wearer Seriously in follow mode. (v) Conclusion: The exoskeleton not only effectively reduced muscle fatigue, but also avoided interfering with the free movement of the wearer.

Crossing the Carotid Siphon: Techniques to Facilitate Distal Access in Tortuous Anatomy: 2-Dimensional Operative Video

As capabilities for endovascular treatment of intracranial vascular pathologies continue to expand, the need for access to the distal internal carotid artery with rigid support catheter systems continues to increase. One of the dominant factors limiting this access is patient anatomy, specifically vessel tortuosity. Increased tortuosity of the carotid siphon is a frequently encountered anatomic variant and may complicate endovascular procedures in adults and children.1,2 Failed attempts to navigate the carotid siphon with a distal access catheter carry a risk of vessel injury and treatment failure. For this reason, techniques that aid in supporting safe advancement of a distal access catheter across a tortuous carotid siphon are essential.3,4 In this video, we demonstrate 2 ways in which this may be accomplished. The first technique uses a larger diameter microcatheter, such as the AXS Offset catheter (Stryker, Kalamazoo, Michigan), to increase support for the distal access catheter, while the second uses a buddy wire technique to accomplish this increased support. Both of these techniques can help increase the safety of navigating a tortuous carotid siphon and increase the likelihood of successful treatment. The procedures shown were performed with the informed consent of the patients.

Investigation of fiber slippage in the chopping process of carbon fiber tows under rigid support

As an important application form of carbon fiber (CF), short CFs and their production process have self-evident research value. In this work, the chopping process of CF tows under rigid support and the essential cause of high cutting forces were explored. Large-tow CFs containing 1–3000 single filaments were chopped, and the fracture processes were observed and described. It was found that obvious fiber slippage phenomena and intermediate fracture behaviors occurred during the chopping process. These factors not only increased the cutting force but also caused an uneven distribution of the cutting force along the width. A mechanical model was established to explain the fiber slippage and intermediate fracture. Based on material mechanics and analytical mechanics, the real process of fiber slippage and intermediate fracture was described by Hamilton’s principle. Moreover, a width constraint experiment was designed to indirectly verify fiber slippage phenomena and intermediate fracture behaviors. Through the analysis of the stress curve, it was proven that a reasonable width constraint could effectively limit fiber slippage and improve the uniformity of the distribution of the cutting force along the width of the tool, thus reducing the cutting force. This work can be used as an excellent guide for the chopping process in CF production.

Analytical determination of application point and normal reaction arm when rolling a wheel on a drum

Evaluation of the rolling resistance of car tires is now often performed on drum stands like car tests. This necessitates the study of the mechanics of interaction between the wheel and the drum in order to determine its force and kinematic characteristics, including the values and points of application of tangential and normal forces in contact with the drum. These problems can be solved taking into account that the mechanics of elastic wheel rolling on a drum is the same as when rolling on a flat rigid support surface. In this paper, from consideration of the mechanics of interaction between an elastic wheel and a drum, using the equations of power balance and force equilibrium of the wheel, the equations for determining the point of normal reaction in contact and its arm relative to the wheel axis during its rolling along one and two drums have been derived.. These dependencies have a simple form and can be applied when considering the rolling of both a single wheel and the car as a whole on a drum stand.

Research of technical and economic indicators of reinforcement of reinforced concrete beams by different technologies

The article presents the results of experimental investigations to determine the destructive force of beams reinforced with external reinforcement and control (without reinforcement). According to the results of such investigations, it can be stated that the strengthening of beam structures by external reinforcement made it possible to increase their bearing capacity by 383.3%. It has been established that both carbon fiber reinforcement using "clamps" and carbon fiber reinforcement are effective.The performed analytical researches established technical and economic indicators of various methods of reinforcement of beam constructions, namely: the addition of additional supports, the addition of additional beams, the external reinforcement of stretched zones by MAPEI technology. As a result, data were obtained indicating that the reinforcement of the crossbar by bringing additional rigid support requires 110.4 man-hours (100%), the reinforcement of the crossbar by bringing additional beams - 94.4 man-hours (85.5%), the reinforcement of the crossbar by external reinforcement - 48 man-hours (43.5%). In this case, the reinforcement of the crossbar by bringing additional rigid support is performed in 9.7 days (100%), the reinforcement of the crossbar by bringing additional beams - 6 days (62%), the reinforcement of the crossbar by external reinforcement - 4 days (41.4%). It is also established that the reinforcement of the crossbar by bringing additional rigid support costs 51.8 thousand UAH (100%), strengthening the structure by bringing additional beams - 58.1 thousand UAH (112%), strengthening the structure by external reinforcement - 35.72 thousand UAH (68.9%).The obtained research results indicate that the labor intensity, duration and cost of reinforcing the beam with external reinforcement is lower compared to other technologies. Efficiency is achieved by a structural component - increasing the bearing capacity without changing the design solution and by technological component - reducing the labor intensity, duration and cost of work.