Radial Compressive Research Articles

Nonlinear behavior analysis of smooth bore unbonded flexible pipes under radial compression

Smooth bore unbonded flexible pipes are widely used to transport oil and gas in offshore fields. Due to its main application in shallow water, the radial bearing capacity is usually designed to be low for economic reasons. If the compressive load applied by tensioner equipment is too high during installation, the flexible pipe will fail due to excessive deformation. In this paper, the nonlinear behavior of smooth bore flexible pipes passing through tensioner equipment was investigated numerically and experimentally. A three-dimensional numerical model considering the nonlinear behavior of the materials, layer-to-layer contacts, and friction for flexible pipe radial compression analysis was established. A radial compression test was conducted to verify the accuracy of the numerical model; Then the numerical model was used to analyze the radial compressive behavior of each layer, and its load-bearing capacities and failure mechanisms were investigated. Finally, a parametric study was performed on the opening angle and number of tensioner tracks. The results of this study can provide a useful reference for the installation of smooth bore flexible pipes.

Dynamic 3D effects of single fiber tensile break within unidirectional composites including resin plasticity, residual stress, interfacial debonding and sliding friction

To study the dynamics of a single fiber tensile break within an S-Glass/epoxy composite and the associated effects of stress wave propagation in the fibers, interface and matrix, a 3D micromechanical Finite Element (FE) model with a hexagonal packing of parallel fibers is developed. The effects of a dynamic fiber break on energy dissipation associated with resin plasticity and interface debonding using cohesive traction laws are included. The 3D FE model also incorporates process-induced residual stresses that induces radial compression at the fiber-matrix interface due the mismatch in CTE and Poisson’s ratios between the fiber and matrix. During dynamic fiber failure where interface debonding occurs, radial compressive residual stresses lead to additional frictional energy dissipation in the debond region of the interface. A map of the dynamic stress concentration factor (SCF) values on the surface (along the axial as well as circumferential directions) of the fibers which are neighboring the fiber break is generated. A stability criterion based on an energy balance between elastic strain energy released by the fiber and energy dissipation (resin plasticity, interphase debonding and frictional sliding) is established to predict maximum fiber strength that initiates unstable debonding of the interface characteristic of axial splitting of the unidirectional composite loaded in tension. The FE modeling results also indicate that the dynamic fiber break introduces strain rates on the order of 106/s in the fiber and matrix, and up to 1012/s in the interphase.

Biomechanical properties of the stomach: A comprehensive comparative analysis of human and porcine gastric tissue

BackgroundStomach-related disorders impose medical challenges and are associated with significant social and economic costs. The field of biomechanics is promising for understanding tissue behavior and for development of medical treatments and surgical interventions. In gastroenterology, animal models are often used when studies on humans are not possible. Often large animal models with similar anatomical characteristics (size and shape) are preferred. However, it is uncertain if stomachs from humans and large animals have similar mechanical properties. The aim of the present study is to characterize and compare hyper- and viscoelastic properties of porcine and human gastric tissue using tension and radial compression tests. Methods: Hyperelastic and viscoelastic properties were quantified from quasi-static ramp tests and stress relaxation tests. Tension in two directions and radial compression experiments were done on intact stomach wall samples as well as on separated mucosa and muscularis layer samples from porcine and human fundus, corpus and antrum. Results and conclusions: Similar hyper- and viscoelastic constitutive models can be used to describe porcine and human gastric tissue. In total, 19 constitutive parameters were compared and results showed significant variations between species. For example, for intact circumferential samples from antrum, the stiffness (a) and relaxation (τ1) were greater for human samples than for porcine samples (p < 0.0001). The constitutive parameters were condition-, region- and layer-dependent and no distinct pattern hereof between species was found. This indicates that different parameters must be used to describe the specific situation. The present work provides insight into porcine and human gastric radial compressive and tensile hyper- and viscoelastic properties, strengthening the inter-species relation of the biomechanical properties. Constitutive relations were established that may aid development and translation of diagnostic or therapeutic devices with computational models.

FEM updating for damage modeling of composite cylinders under radial compression considering the winding pattern

This work aims at developing a strategy to obtain damage evolution parameters of wound cylinders to verify the influence of the winding pattern on them. First, a detailed description of the pattern generation is presented. Then, a finite element (FE) model is developed, in which the cylinders are constructed with winding patterns (WP) of 1/1, 2/1, and 3/1 and subjected to radial compressive loading. Since the cylinder-to-plate contact is considered, the variation of radial stiffness with respect to the parallel plate position is also analyzed. In addition, a damage model is used to predict the progressive failure of those cylinders. A finite element model updating (FEMU) routine is then developed to find the damage input parameters that best simulate experimental force–displacement curves. Key results show that the FEMU algorithm is strongly dependent on the initial guesses producing, however, an excellent correlation with experimental data. The predicted force versus displacement curves for all winding patterns are within the experimental standard deviation, except for the cases in which the winding pattern is not taken into consideration. The computational framework proposed is validated both quantitatively and qualitatively through post-mortem analysis of the specimens. The winding pattern affects the failure and damage mechanisms of the cylinders and, consequently conventional FE models that disregard the pattern cannot capture these mechanisms.

Compressive Failure Mechanism of Structural Bamboo Scrimber.

Bamboo scrimber is one of the most popular engineering bamboo composites, owing to its excellent physical and mechanical properties. In order to investigate the influence of grain direction on the compression properties and failure mechanism of bamboo scrimber, the longitudinal, radial and tangential directions were selected. The results showed that the compressive load–displacement curves of bamboo scrimber in the longitudinal, tangential and radial directions contained elastic, yield and failure stages. The compressive strength and elastic modulus of the bamboo scrimber in the longitudinal direction were greater than those in the radial and tangential directions, and there were no significant differences between the radial and tangential specimens. The micro-fracture morphology shows that the parenchyma cells underwent brittle shear failure in all three directions, while the fiber failure of the longitudinal compressive specimens consisted of ductile fracture, and the tangential and radial compressive specimens exhibited brittle fracture. This is one of the reasons that the deformation of the specimens under longitudinal compression was greater than those under tangential and radial compression. The main failure mode of bamboo scrimber under longitudinal and radial compression was shear failure, and the main failure mode under tangential compression was interlayer separation failure. The reason for this difference was that during longitudinal and radial compression, the maximum strain occurred at the diagonal of the specimen, while during tangential compression, the maximum strain occurred at the bonding interface. This study can provide benefits for the rational design and safe application of bamboo scrimber in practical engineering.

Numerical design optimization of the fiber orientation of glass/phenolic composite tubes based on tensile and radial compression tests

Phenolic-based composite tubes are being used in industry due to their high fire resistant and lower yields of heat and toxic fumes. These tubes can be better designed by changing the ply-orientation to meet desired performance requirements. This study aims to numerically evaluate the influence of the winding angle and stacking sequence on the mechanical performance of glass/phenolic composite tubes subjected to tensile and radial compression loadings. An extensive study, using the LS-DYNA finite element software, was employed to obtain the optimal ply angle and layup condition of the tubes. The numerical results were in good agreement with the experimental data. Failure modes, tensile stress versus percentage elongation behavior, load–displacement behavior, and stiffness of the tubes were investigated. The behavior of the tubes was found to be highly dependent on the winding angles and stacking sequence, i.e., the specimens with fibers at ± 75° and ± 80° presented the best radial compressive characteristics, whereas those wound at ± 55° performed better under coupon tensile testing. In addition, following the design guidelines of using balanced, symmetric, and homogeneous stacking sequence with 10% of plies in the ± 45° , instead of the classical unidirectional ply [ ±θ] can lead to significantly improved optimal designs.

Radial crushing response of ex-situ foam-filled tubes at elevated temperatures

The current research investigates the mechanical properties and deformation mechanisms of foam-based composites under radial compressive loadings at different temperatures between 25 to 450 °C. The radial compression tests are performed at 10 mm·min−1 on aluminum foams (AFs), empty tubes (ETs) and foam-filled tubes (FFTs) within a heating chamber. The obtained force–displacement curves are analyzed to investigate the main mechanical properties of the samples such as yield, plateau and densification forces. The deformation mechanism of each individual component is studied at room temperatures. According to obtained results, the radial compression of AFs does not show any shear failure in the early stages of their deformation at room temperature. Instead, the shearing delays at higher displacement during the radial loading of AFs. In addition, unlike axial loadings, the radial compression of the ETs does not progress through successive folding at all tested temperatures. The interaction effect between tubes and foams is observed at all testing temperatures, highlighting a maximum at temperatures close to room temperature. The mechanical properties of FFTs outperform the AFs and ETs. However, at temperatures close to melting point of AF, there is no significant difference in energy absorption capacity of the FFTs and ETs.

Statistical modelling and optimization of print quality and mechanical properties of customized tubular scaffolds fabricated using solvent-based extrusion 3D printing process.

Tissue-engineered tubular scaffolds offer huge potential to heal or replace the diseased organ parts like blood vessels, trachea, oesophagus and ureter. However, manufacturing these scaffolds in various scales and shapes is always challenging and requires progressive technology. Developing a flexible and accurate manufacturing method is a major developmental direction in the field of tubular scaffold fabrication. In this context, the present work presents a novel solvent-based extrusion 3D printing which allows extruding over a rotating mandrel to fabricate tubular scaffolds of polycaprolactone (PCL) and polyurethane (PU). Experimental runs were planned as per the central composite design (CCD) to evaluate the effects of input parameters like infill density, layer thickness, print speed and percentage of PU on the output responses like printing quality and mechanical characteristics. The printing quality was quantified by measuring average surface roughness of the printed scaffolds and mechanical properties were evaluated by measuring radial compressive load, and percentage of elongation. The experimental investigations revealed that printing quality was improved at higher infill densities and was deteriorated at higher print speeds and layer thicknesses. Similarly, the radial compressive load was improved with the increase in infill density and was decreased with an increase in layer thickness, print speed and percentage of PU. The percentage of elongation was found to improve at higher infill densities and percentages of PU and was reduced with an increase in layer thickness and print speed. Additionally, a multi-objective optimization using Genetic Algorithm was used to evaluate the optimum conditions to minimize surface roughness and maximizing radial compression load and percentage of elongation. Finally, a case study was performed by comparing the mechanical properties of tubular organs and scaffolds from the existing reports and results of the present work.

Creep and Residual Properties of Filament-Wound Composite Rings under Radial Compression in Harsh Environments.

This work focuses on the viscoelastic response of carbon/epoxy filament-wound composite rings under radial compressive loading in harsh environments. The composites are exposed to three hygro-thermo-mechanical conditions: (i) pure mechanical loading, (ii) mechanical loading in a wet environment and (iii) mechanical loading under hygrothermal conditioning at 40 C. Dedicated equipment was built to carry out the creep experiments. Quasi-static mechanical tests are performed before and after creep tests to evaluate the residual properties of the rings. The samples are tested in (i) radial compression, (ii) axial compression, and (iii) hoop tensile strength. Different laminates wound at off-axis orientations are manufactured via filament winding and analyzed. Key results show that creep displacement is affected by both hygrothermal and mechanical conditionings, especially at a higher temperature. Moreover, residual properties are quantified showing that creep generates permanent damage in the cylinders.

Stiffness Analysis of Reinforced Ureteral Stents Against Radial Compression: In vitro Study.

IntroductionMalignant ureteral obstruction caused by cancer diseases may induce renal failure. Indwelling stent is a popular method to release renal obstruction. But adequate stent placement across an obstructed ureter does not necessarily guarantee renal decompression. The aim of the study was to compare, in vitro, the physical characteristics and stiffness of several commercially available reinforced ureteral stents and identify the physical factors that could lead to the obstruction of the stent.Material and MethodsThe test apparatus used for measurements allowed applying a radial compression force on a segment of the stent to stop a water flow through the lumen of the stent. Some reinforced double-pigtail stents Teleflex Medical, Bard, and Coloplast were evaluated.ResultsThe best physical-stiffness characteristic was obtained with the Teleflex 8F stent (5.4 N mm−2). The best result against the radial compression was obtained with tandem stents. The radial compressive stresses of the Teleflex stents (4.4 to 5.4 N mm−2) were higher than with the other stents used in the study (1.0 to 2.9 N mm−2). Among the reinforced stents selected in the present study, a wider inner diameter helped increase volumetric flow rate but did not affect the stiffness of the stent. The measurement of inner diameter showed heterogeneity along the tube of some stents.ConclusionThe stiffness of the stent appeared to be an important factor to maintain patency with respect to radial compression forces but the inner diameter of the stent and its preservation may be essential parameters to increase the volumetric flow rate. Some reinforced stents tested in the present study confirmed that it is possible to combine stiffness and wide lumen. The use of tandem stents provided the best stiffness against radial compression and the greatest lumen.

Axial and radial compressive properties of alumina-aluminum matrix syntactic foam filled thin-walled tubes

The alumina-aluminum matrix syntactic foam filled thin-walled tubes (FFTs) were prepared by inserting aluminum matrix syntactic foams reinforced with alumina hollow spheres with three size ranges (1.0–1.5 mm, 1.5–2.0 mm and 2.5–3.0 mm) into empty aluminum alloy tubes. For comparison with as cast samples, each type of syntactic foam underwent a T6 heat treatment. The FFTs and individual components were compressed in axial and radial directions. During axial compression, FFTs deformed by concertina mode, which was different from the diamond mode of tubes and the deformation characteristics of syntactic foams dominated by brittle fracture. The deformation mode of FFTs under radial compression was consistent with syntactic foams. The axial energy absorption was always greater than the radial energy absorption for FFTs and individual components under the same conditions. Regardless of the compression direction, the energy absorption of FFTs was higher than the sum of individual components. The energy absorption varied with hollow sphere size and heat treatment. The axial interaction effect between syntactic foam and tube in FFTs increased with deformation. The FFTs exhibited excellent specific energy absorption under axial and radial compression.

Mechanical response of filament wound composite rings under tension and compression

This study aims at evaluating the influence of the winding angle, stacking sequence and diameter-to-thickness ratio on the mechanical response of composite rings subjected to radial compression, axial compression and hoop tensile loadings. The rings were obtained from filament wound tubes. The rings were found highly dependent on the winding angle, i.e. the specimens with fibers at ±90° presented the best radial compressive characteristics, whereas those wound at ±60° performed best under axial compression, and apparent hoop tensile strength determined via split disk testing was higher for rings wound at ±90°. All rings were dependent on the diameter-to-thickness ratio. Failure was studied through micrographs of post-mortem specimens. The dominant failure modes for radial compression, axial compression and hoop tensile loadings were, respectively, delamination, delamination and minor off-axis cracks, and fiber/matrix debonding and fiber breakage.

3466 Innovative 3D Printed Intravaginal Rings: Developing AnelleO PRO, the First Intravaginal Ring for Infertility

OBJECTIVES/SPECIFIC AIMS: The study aims to develop and test a biocompatible 3D-printed IVRs for the mechanical and release properties of a model drug, β-estradiol, then translate these methods to the target drug, progesterone. The goals include demonstrating decoupling of mechanical and release properties of the rings, release profiles driven by geometry and efficacy in sheep animal models to evaluate device safety. METHODS/STUDY POPULATION: A novel 3D-printing platform, continuous liquid interface production (CLIP), pioneered by Carbon, enables the fabrication of complex designs on a timescale that is amenable to manufacturing. The process utilizes computational-aided design (CAD), specifying shape and geometry, which is recreated via a photopolymerization process. IVRs are fabricated with CLIP using a biocompatible resin at a rate of approximately 15 min. per ring. Rings were fabricated and assessed for the release of a model drug, β-estradiol. The process was then translated to the target drug, progesterone. Rings were evaluated for radial compression and in vitro release in simulated vaginal fluid (SVF). RESULTS/ANTICIPATED RESULTS: Intravaginal rings (IVRs) were designed and fabricated to be geometrically complex in an effort to control release. Ring geometry and subsequent pore size was achieved through the use of unit cells. Several design parameters were explored including unit cell type, size, and band presence in two resins of differing mechanical properties. Through design, a wide range of radial compressive properties were achieved which spanned values covered by commercially available rings. The release of β-estradiol in SVF was found to span 57 – 115 days and resulted in near or complete release of the total loaded drug. Changing the internal geometric design of the ring was found to have minimal influence on the compression properties, thus the mechanical and release characteristics of the rings were largely decoupled. DISCUSSION/SIGNIFICANCE OF IMPACT: This is a novel approach to the design and fabrication of intravaginal rings for the treatment of infertility. The use of CAD and the decoupling of release from mechanical properties allows for us to move away from the one-size one-dose fits all approach to IVRs.

Radial Compressive Property and the Proof-of-Concept Study for Realizing Self-expansion of 3D Printing Polylactic Acid Vascular Stents with Negative Poisson's Ratio Structure.

Biodegradable stents offer the potential to reduce the in-stent restenosis by providing support long enough for the vessel to heal. The polylactic acid (PLA) vascular stents with negative Poisson’s ratio (NPR) structure were manufactured by fused deposition modeling (FDM) 3D printing in this study. The effects of stent diameter, wall thickness and geometric parameters of arrowhead NPR structure on radial compressive property of 3D-printed PLA vascular stent were studied. The results showed that the decrease of stent diameter, the increase of wall thickness and the increase of the surface coverage could enhance the radial force (per unit length) of PLA stent. The radial and longitudinal size of PLA stent with NPR structure decreased simultaneously when the stent was crimped under deformation temperature. The PLA stent could expand in both radial and longitudinal direction under recovery temperature. When the deformation temperature and recovery temperature were both 65 °C, the diameter recovery ratio of stent was more than 95% and the maximum could reach 98%. The length recovery ratio was above 97%. This indicated the feasibility of utilizing the shape memory effect (SME) of PLA to realize the expansion of 3D-printed PLA vascular stent under temperature excitation.

Damage modeling for carbon fiber/epoxy filament wound composite tubes under radial compression

The focus of this study is the development of a computational model with damage to predict failure of carbon fiber/epoxy filament wound composite tubes under radial compressive loading. Numerical analysis is performed via Finite Element Method (FEM) with a damage model written as a UMAT (User Material Subroutine) and linked to commercial software. The experimental analysis carried out followed ASTM D2412-11, where the specimen is parallel-loaded by two steel-based plates. Three stacking sequences have been evaluated. Both numerical and experimental results show that the presence of hoop layers at inner and outer layers plus ±75° non-geodesic layers gives maximum compressive load to the composite tube, since the reinforcement is wound closer to the loading direction. Moreover, failure modes are predominantly delaminations, which are confirmed via numerical analyses through high in-plane shear stresses levels, and via experimental analyses through stereoscopic micrographs.

Boron-Filled Hybrid Carbon Nanotubes.

A unique nanoheterostructure, a boron-filled hybrid carbon nanotube (BHCNT), has been synthesized using a one-step chemical vapor deposition process. The BHCNTs can be considered to be a novel form of boron carbide consisting of boron doped, distorted multiwalled carbon nanotubes (MWCNTs) encapsulating boron nanowires. These MWCNTs were found to be insulating in spite of their graphitic layered outer structures. While conventional MWCNTs have great axial strength, they have weak radial compressive strength, and do not bond well to one another or to other materials. In contrast, BHCNTs are shown to be up to 31% stiffer and 233% stronger than conventional MWCNTs in radial compression and have excellent mechanical properties at elevated temperatures. The corrugated surface of BHCNTs enables them to bond easily to themselves and other materials, in contrast to carbon nanotubes (CNTs). BHCNTs can, therefore, be used to make nanocomposites, nanopaper sheets, and bundles that are stronger than those made with CNTs.

Mechanical evaluation of gradient electrospun scaffolds with 3D printed ring reinforcements for tracheal defect repair

Tracheal stenosis can become a fatal condition, and current treatments include augmentation of the airway with autologous tissue. A tissue-engineered approach would not require a donor source, while providing an implant that meets both surgeons’ and patients’ needs. A fibrous, polymeric scaffold organized in gradient bilayers of polycaprolactone (PCL) and poly-lactic-co-glycolic acid (PLGA) with 3D printed structural ring supports, inspired by the native trachea rings, could meet this need. The purpose of the current study was to characterize the tracheal scaffolds with mechanical testing models to determine the design most suitable for maintaining a patent airway. Degradation over 12 weeks revealed that scaffolds with the 3D printed rings had superior properties in tensile and radial compression, with at least a three fold improvement and 8.5-fold improvement, respectively, relative to the other scaffold groups. The ringed scaffolds produced tensile moduli, radial compressive forces, and burst pressures similar to or exceeding physiological forces and native tissue data. Scaffolds with a thicker PCL component had better suture retention and tube flattening recovery properties, with the monolayer of PCL (PCL-only group) exhibiting a 2.3-fold increase in suture retention strength (SRS). Tracheal scaffolds with ring reinforcements have improved mechanical properties, while the fibrous component increased porosity and cell infiltration potential. These scaffolds may be used to treat various trachea defects (patch or circumferential) and have the potential to be employed in other tissue engineering applications.

Numerical Simulation of the Shape Memory Alloy Pipe Joint

Based on the existing constitutive model of shape memory alloys (SMA), as well as on the state of stress distribution between the pipe and pipe joint, a simplified constitutive model for SMA can indeed fit the SMA pipe coupling structure. Using this constitutive model to simulate the stress distribution during the process of heating up, we can use the system to discuss the relationship between the radial compressive stress and various influencing factors. KeywordsShape Memory Alloys; Constitutive Model; Radial Compressive Stress; Pipe Joint; Wall Thickness

Surface stress effects on the postbuckling behavior of geometrically imperfect cylindrical nanoshells subjected to combined axial and radial compressions

Because of surface free energy effects at nanoscale, study of the mechanical behavior of nanostructures including surface stress effects is a topic of substantial interest. Herein, the nonlinear buckling and postbuckling characteristics of geometrically imperfect cylindrical nanoshells under combined axial and radial compressive loads are investigated in the presence of surface stress effects. An efficient size-dependent shell model is proposed based on Gurtin–Murdoch elasticity theory and von Karman–Donnell-type of kinematic nonlinearity. On the basis of variational approach using the principle of virtual work, the non-classical governing differential equations are derived. Afterwards, a boundary layer theory is employed incorporating surface stress effects in conjunction with nonlinear prebuckling deformations, initial geometric imperfections and large postbuckling deflections. Then a two-stepped singular perturbation methodology is put to use in order to solve the size-dependent nonlinear problem corresponding to axial dominated and radial dominated loading cases. It is shown that in the case of radial dominated loading, the combination of hydrostatic pressure with axial compression causes to decrease approximately the effect of surface stress compared to the absence of axial load. However, for the axial dominated loading case, in comparison with no applied radial load, the surface stress effects is more significant in the presence of hydrostatic pressure.

Nonlinear buckling and postbuckling behavior of cylindrical nanoshells subjected to combined axial and radial compressions incorporating surface stress effects

In the present study, the Gurtin-Murdoch elasticity theory, as a theory capable of capturing size effects, is implemented to predict the nonlinear buckling and postbuckling response of cylindrical nanoshells under combined axial and radial compressive loads in the presence of surface stress effects. For this purpose, a size-dependent shell mode containing geometric nonlinearity is proposed within the framework of the classical shell theory. Because it is necessary to satisfy balance conditions on the surfaces of nanoshell, it is assumed that the normal stress component of the bulk varies linearly through the shell thickness. On the basis of a variational formulation using the principle of virtual work, the non-classical governing differential equations are derived. Subsequently, a boundary layer theory is employed including the nonlinear prebuckling deformations and the large deflections in the postbuckling regime. Then a two-stepped perturbation methodology is utilized to obtain the size-dependent critical buckling loads and the postbuckling equilibrium paths of nanoshells corresponding to the axial dominated and radial dominated loading cases. It is revealed that in the radial dominated loading case, a positive value of surface elastic constants leads to increase the critical buckling load but decrease the critical end-shortening of nanoshell. However, in the axial dominated loading case, surface elastic constants with positive sign causes to increase the both critical buckling load and critical end-shortening of nanoshell.