The Effect of Heavy-Duty Vehicle Crossings on the State of Stress of Buried Pipelines

The aim of this article is to quantify the loads exerted by heavy-duty vehicles when crossing over buried pipeline. This problem arises in connection to the question pertaining to the use of protective sleeves (casings) applied to gas pipelines in regions with increased demands on pipeline operation safety. An experiment was conducted on a test pipe section made from L360NE pipeline steel equipped with strain gauges along the pipe perimeter, measuring strains in the axial and circumferential directions. Strain measurements were taken after back-filling the pipe trench, then during vehicle crossings over the empty pipe, and again after pressurizing the test pipe with air. Strain-based hoop stresses at the surface of the empty test pipe were found to exceed 30 MPa after back-filling the trench and increased to more than 40 MPa during the vehicle crossings. Similarly, axial stresses reached extremes of around 17 MPa in compression and 12 MPa in tension. Applying internal air pressure to the test pipe resulted in a reduced net effect on both the hoop and axial stresses.

Loosening of Posteromedial Meniscal Root Repairs Affects Knee Mechanics: A Finite Element Study

Meniscal root repairs are susceptible to unrecoverable loosening that may displace the meniscus from the initial position reduced during surgery. Despite this, the effects of a loosened meniscal root repair on knee mechanics are unknown. We hypothesized that anatomic root repairs without loosening would restore knee mechanics to the intact condition better than loosened anatomic root repairs, but that loosened repairs would restore mechanics better than untreated meniscal root tears. Finite element knee models were used to evaluate changes in cartilage and meniscus mechanics due to repair loosening. The mechanical response from loosened anatomic root repairs was compared to anatomic repairs without loosening and untreated root tears. All conditions were evaluated at three flexion angles, 0°, 30°, and 60°, and a compressive force of 1,000 N to simulate return-to-activity loading. The two-simple-suture method was represented within the models to simulate posteromedial meniscal root repairs and repair loosening was derived from previous biomechanical experimental data. Loosening decreased hoop stresses throughout the meniscus, increased posterior extrusion, and shifted loading through the meniscus-cartilage region to the cartilage-cartilage region compared to the anatomic root repair without loosening. Despite differences between repairs and loosened repairs, the changes from loosened repairs more closely resembled the anatomic repair without loosening than the untreated root repair condition. Therefore, root repairs are susceptible to loosening that will prevent a successful initial repair from remaining in the intended position and will alter mechanics, although repairs that loosen appear better than leaving tears untreated.

Meniscal Root Repair

Background: Meniscal root tears typically result from a hyperflexion/squatting injury or are in conjunction with ligamentous knee injury. Once a complete tear occurs, the meniscus is unable to convert axial loads to transverse hoop stresses which result in increased tibiofemoral contact pressure and osteoarthritis. The goal of a meniscal root repair is to anatomically reattach the meniscal root to the tibia plateau. Complete and partial healing occurs in over 93% of cases with retear rates ranging from 0% to 7%. Indications: We present a case of a highly active 21-year-old male collegiate soccer play that sustained a medial meniscal root tear after slipping on ice. Technique: An anatomic medial meniscal root repair was performed using a transtibial guide and 2 loop sutures tied over a button. Results: Full anatomic footprint coverage was able to be achieved intraoperatively and gentle range of motion from 0 to 90° of flexion did not result in gap formation. Discussion/Conclusion: Successful outcomes with full anatomic footprint coverage of the medial meniscal root can be achieved with 2-loop suture button configuration.

Subsea FRP pipeline performance in external pressure: Failure and external pressure-induced buckling

The Subsea pipelines are subjected to high hoop stresses due to the hydrostatic pressure. When the internal pressure of the liquid has a higher value than the external hydrostatic one, there is a balance of the tensile and compressive stresses. However, during the offshore installation, the subsea pipelines are empty and the compression due to the hydrostatic pressure of the sea is predominant. High compressive stresses in FRP pipelines can cause failure or buckling. In the present work, an investigation of the external pressure-induced failure and buckling is carried out. Analytical formulae and results are provided and discussed.

A reverse transition route from inertial to elasticity-dominated turbulence in viscoelastic Taylor–Couette flow

A high-order transition route from inertial to elasticity-dominated turbulence (EDT) in Taylor–Couette flows of polymeric solutions has been discovered via direct numerical simulations. This novel two-step transition route is realized by enhancing the extensional viscosity and hoop stresses of the polymeric solution via increasing the maximum chain extension at a fixed polymer concentration. Specifically, in the first step inertial turbulence is stabilized to a laminar flow much like the modulated wavy vortex flow. The second step destabilizes this laminar flow state to EDT, i.e. a spatially smooth and temporally random flow with a $-3.5$ scaling law of the energy spectrum reminiscent of elastic turbulence. The flow states involved are distinctly different to those observed in the reverse transition route from inertial turbulence via a relaminarization of the flow to elasto-inertial turbulence in parallel shear flows, underscoring the importance of polymer-induced hoop stresses in realizing EDT that are absent in parallel shear flows.

A System Identification and Implementation of a Soft Sensor for Freeform Bending

The primary goal of this study is the formulation of a soft sensor that predicts industrially relevant mechanical properties for freeform bending. This serves as the foundation of a closed-loop property control. It is hypothesized that by inline measurement of hardness, predictions regarding residual hoop stresses, local strength and strain level can be achieved. A novel hardness-based correlation scheme is introduced, which is implemented into an extended Kalman filter (EKF) and allows an inline prediction of local strength, residual hoop stresses and plasticity. Furthermore, the ultrasonic contact impedance (UCI) method is validated as a suitable inline measuring solution.

The Problems of Meniscal Root Tears

Meniscal root tears are defined as radial tears located within 1 cm from the meniscal attachment or a bony root avulsion. This injury is biomechanically comparable to a total meniscectomy, leading to compromised hoop stresses resulting in decreased tibiofemoral contact area and increased contact pressures in the involved compartment. These changes are detrimental to the articular cartilage and ultimately lead to the development of early osteoarthritis. Surgical repair is the treatment of choice in patients without significant osteoarthritis (Outerbridge grades 3 or 4). Root repairs have been reported to improve clinical outcomes, decrease meniscal extrusion and slow the onset of degenerative changes. In this article, we describe the anatomy, biomechanics, clinical evaluation, treatment methods, outcomes, and post-operative rehabilitation for posterior meniscal root tears.

Cold Expansion Process with Multiple Balls—Numerical Simulation and Comparison with Single Ball and Tapered Mandrels

Cold expansion technology is an extended method used in aeronautics to increase fatigue life of holes and hence extending inspection intervals. During the cold expansion process, a mechanical mandrel is forced to pass along the hole generating compressive residual hoop stresses. The most widely accepted geometry for this mandrel is the tapered one and simpler options like balls have generally been rejected based on the non-conforming residual hoop stresses derived from their use. In this investigation a novelty process using multiple balls with incremental interference, instead of a single one, was simulated. Experimental tests were performed to validate the finite element method (FEM) models and residual hoop stresses from multiple balls simulation were compared with one ball and tapered mandrel simulations. Results showed that the use of three incremental balls significantly reduced the magnitude of non-conforming residual hoop stresses and the extension of these detrimental zone.

Recommended Stress Formulae for Tubular Conical Transition Designs

For the design of tubular conical transitions, the axial, bending, and hoop stresses at the junctions are required. Among the offshore design standards, API RP-2A, ISO 19902, and NORSOK N-004, various equations exist for the same stress quantity which may cause confusions. The quality of these existing stress formulae will be examined in this paper. The tubular conical stress equations used in the offshore industry started from Boardman’s studies in the 1940s. Recently, Lotsberg re-formulated this problem and applied the results to stress concentration factor (SCF) applications. This paper solves the same set of shell equations but the formulations are cast in a different form. This new format allows for an in-depth examination of existing code equations. In addition, the formulation as presented can be used for modifications to gain higher accuracy. Several recommended new stress formulae are provided. It is observed that the existing code provisions’ accuracy quickly deteriorates for cases where plate thickness in tubular and cone differ. The recommended approach is based on theoretical framework of shell mechanics, which better facilitate tubular/cone force balances when compared with existing equations. The sectional relationships among moment, shear, and hoop loads are also treated consistently using shell theory. The resulted improvements make the recommended formulae more accurate than the existing provisions.