Failure Of Rods Research Articles

Penetration performance and failure of long rods impacting aluminum targets

A numerical study concerning the deep penetration of long steel rods into 6061-T6511 aluminum targets at high impact velocities is presented. The range of impact velocities where these rods lose their penetration capability due to their nose deformation, or impact inclination, is explored. The numerical simulations follow several complex phenomena such as the onset of rod deformation and erosion, encountered in the tests with spherical and ogive nosed rods. It turns out that penetration depth decrease of spherical nosed rods at high impact velocities, is due to their nose deformation, while ogive nosed rods are more sensitive to impact inclination. At very high impact velocities both types of rods experience significant mass erosion, and their penetration process can be described by conventional hydrodynamic penetration model for eroding rods. The numerical simulations in this work are shown to follow test results for spherical and ogive nosed rods, impacting an aluminum alloy target at a large range of impact velocities. We show that these agreements can be achieved with relatively simple constitutive relations for the steel rods and the aluminum target.

Safety considerations related to boron redistribution during Loss-of-Coolant-Accident initiated beyond design basis events for the NuScale power module

The authors, as staff at the U.S. Nuclear Regulatory Commission (NRC), evaluated the potential consequences of boron dilution under beyond design basis conditions in the NuScale Power Module to inform NRC staff’s safety evaluation report for the NuScale design certification review. The authors identified the small break loss of coolant accident with coincident failure of control rods to insert as the scenario with the most adverse boron dilution and reactivity insertion consequences. The authors evaluated the sequence of events for the scenario to determine which conditions or phenomena could produce the potential for a core flow surge to yield core damage because of a super-prompt reactivity excursion. The authors screened the conditions and phenomena that could potentially cause a core flow surge based on the dynamic speed of the incursion compared to key reactivity feedback mechanisms: thermal–hydraulic coupling via rod heat transfer and convective mixing. Based on the screening process, the authors were able to identify two processes that could potentially lead to a power excursion. However, the authors’ analysis relies heavily on assumptions regarding convective mixing, making this an important phenomenon worth careful consideration in any evaluation of boron redistribution.

An innovative type of module-to-core wall connections for high-rise steel modular buildings

High-rise steel modular buildings are normally designed and constructed using a structural system that consists of cast-in-situ concrete for the stability core and steel-framed volumetric modules for residential areas. In such systems, various connections, such as the module-to-core wall (M2C) connection, play a critical role in the lateral loading transfer and structural response. However, there is a lack of systematic understanding of the mechanical behaviours of M2C connections in high-rise buildings under dominant lateral effects. This study aims to develop an innovative fully bolted type of M2C connection to address lateral loads, such as the strong wind effects of high-rise buildings. This study was conducted by combining a comprehensive literature review of connection designs of high-rise steel modular buildings and a case study using a 31-storey student hostel building in Hong Kong. Under monotonic sliding and cyclic loading, the developed type of M2C connection was found to have good mechanical properties. The resistance of the developed connection was found to be governed by the bending capacity of the steel beams of the modules under cyclic loading, whereas the failure of the developed connection resulted from the shear failure of the anchor rods under monotonic sliding. Four design principles were proposed for the developed connection type to improve its capacity and ductility. The findings should provide a theoretical reference and practical guidance to design M2C connections in high-rise steel modular buildings. • High-rise steel modular buildings present mixed-type deformation under lateral loads. • Semi-rigid conceptual model was proposed for module-to-core-wall connections based on deformation and stiffness property. • An innovative fully bolted module-to-core-wall connection was developed with construction efficiency. • The developed module-to-core-wall connection type was examined with good mechanical properties. • Four design principles were proposed for module-to-core-wall connections in steel modular buildings.

Reinforced concrete beams externally strengthened by CFRP rods with steel plate, anchorage bolts, and concrete jacketing

This study proposed a new scheme for the retrofitting of Reinforced Concrete (RC) beams using Carbon Fiber Reinforced (CFRP) rods restrained using steel plates and anchorage bolts called the mechanical anchorage system (MAS). This system also employed an external concrete jacket to cover the MAS and CFRP rods. The performance of the proposed technique was experimentally assessed using the four-point flexural testing of retrofitted beams under incremental cyclic load using a dynamic actuator. A total of eight beams were cast and tested in different configurations to determine the effectiveness of the design parameters including the number of CFRP rods, the contribution of MAS, and concrete jacketing (CJ) in terms of load capacity, cracking, failure mode, and ductility. The results revealed that the efficiency of the proposed retrofitting system was achieved by increasing the load capacity of retrofitted beams and preventing the premature debonding failure of CFRP rods. Although de-bonding can occur on the surface between the old and new concrete, the utilization of a perfect adhesive epoxy on the concrete contact surface led to sufficient bonding between the two surfaces. Therefore, overall, the proposed strengthening technique can be considered a reliable method to enhance the performance of RC beams without the risk of de-bonding.

Damage Diagnosis of Single-Layer Latticed Shell Based on Temperature-Induced Strain under Bayesian Framework.

Under the framework of Bayesian theory, a probabilistic method for damage diagnosis of latticed shell structures based on temperature-induced strain is proposed. First, a new damage diagnosis index is proposed based on the correlation between temperature-induced strain and structural parameters. Then, Markov Chain Monte Carlo is adopted to analyze the newly proposed diagnosis index, based on which the frequency distribution histogram for the posterior probability of the diagnosis index is obtained. Finally, the confidence interval of the damage diagnosis is determined by the posterior distribution of the initial state (baseline condition). The damage probability of the unknown state is also calculated. The proposed method was validated by applying it to a latticed shell structure with finite element developed, where the rod damage and bearing failure were diagnosed based on importance analysis and temperature sensitivity analysis of the rod. The analysis results show that the proposed method can successfully consider uncertainties in the strain response monitoring process and effectively diagnose the failure of important rods in radial and annular directions, as well as horizontal (x- and y-direction) bearings of the latticed shell structure.

Modeling the Multicyclic Fatigue Failure of Rods under Symmetrical Tension/Compression

Modeling the Multicyclic Fatigue Failure of Rods under Symmetrical Tension/Compression

Effect of fiber hybridization types on the mechanical properties of carbon/glass fiber reinforced polymer composite rod

In order to balance the cost performance of carbon and glass fibers, the unidirectional carbon/glass hybrid fiber reinforced polymer composite rods were developed through the pultrusion technology in the present paper. Two kinds of fiber hybridization types were proposed including intra-yarn hybrid (uniform dispersed hybrid, UDH) and inter-layer hybrid (core-shell hybrid, CSH). Furthermore, the effects of fiber hybridization types on the mechanical properties (interface/short beam shear strength, three-point bending strength and tensile strength) were investigated experimentally. The full-field strain was obtained through the digital image correlation method to reveal the hybrid mechanism. It was found that the effects of fiber hybridization types on mechanical properties were remarkable. Through uniformly dispersing the carbon fiber into the glass fiber, the maximum increase percentages of available strength were up to 10.9% for short beam shear, 60.3% for three-point bending and 58.7% for tensile strength, respectively. The results of full-field strain analysis revealed that the mechanical failure of CSH rods was dominant by the interface debonding of shell/core, which significantly decreased the mechanical properties. In comparison, UDH rods had the intact interface bonding of carbon/glass fiber/resin, the mechanical failure was derived from the fracture of carbon fiber. The tensile strength of carbon fiber was fully utilized, which contributed to the higher mechanical properties. The larger scale carbon fiber tow may form the weaker interface layer of carbon/glass fiber/resin, which led to uneven interface stress distribution under the external loading and the decrease of interface shear strength.

Experimental study of concrete breakout failure mechanism in an exposed column base with a foundation beam

Exposed column bases are extensively used in low-to-medium rise steel structures. However, the stress transfer mechanism in the column base is extremely complicated at various failure modes. One of the failure modes mentioned in the Japanese design recommendations involves the yielding and fracture of anchor rods. To ensure this failure mode, the pull-out failure of the anchor rods—one of the reasons responsible for the concrete breakout failure—has to be prevented. However, in Japan, the current design recommendation regarding the concrete breakout failure is not clear, and the studies that have focused on this topic are limited in number. In this study, experiments were conducted to clarify: 1) the concrete breakout failure mechanism, and 2) the effects of the foundation beam reinforcement on the concrete breakout failure. A total of nine specimens, with varied configurations in anchor rods, foundation beam reinforcement, concrete strength, among others, were loaded to failure. According to the experimental results, the column rebar started to transfer strength after the tension of anchor reached the strength of concrete breakout failure. The current design recommendation overestimates the number of effective column rebars on the concrete breakout failure. As for the contribution of concrete, it decreased as the conical cracks occurred and became stable afterwards. Meanwhile, the foundation beam rebar exhibited negligible effect on the concrete breakout failure. Based on the experimental observations, a stage-wise approach is proposed to quantify the contributions of both the concrete and column reinforcement on the concrete breakout failure of an exposed column base.

Temperature Dependent Dynamic Strain Localization and Failure of Ductile Polymeric Rods under Large Deformation

Ductile polymers have been increasingly applied in engineering applications to enhance the structural reliability under impact loading. Due to the limitation of experimental setup to achieve large tensile deformation and the difficulty to achieve dynamic force equilibrium, the localization and post-necking stages up to fracture of ductile polymers at high strain rates have less been investigated. In the present work, the dynamic strain localization of ductile polymeric rods under large tensile deformation up to fracture is studied on the bespoke Hopkinson tension bar synchronized with a high-speed camera. Transparent polycarbonate (PC) is used as a model material in the present study. Likewise, the constitutive response and fracture behaviour of polycarbonate are also characterized with the assistance of Digital Image Correction (DIC) from low to high strain rates under various temperature conditions. The results quantitatively show that the dynamic local strain rate initially increases dramatically to 200 % of the nominal strain rate due to strain localization. This is followed by a rapid drop with necking propagation, and finally tends to stay at strain rate of approximately 20 % of the nominal strain rate until fracture. The elevated temperatures would result in higher local strain rates. Two constitutive models with and without the consideration of constant strain rate condition are constructed for PC and incorporated in finite element simulations. The trend of dynamic local strain rate history with respect to nominal strain rate is successfully reproduced in simulations. The constitutive models particularly the simple dynamic amplification model, are able to reflect the phenomenological key features of the experimentally observed macroscopic and local responses of polycarbonate, and would find their potential applications in impact resistant transparency design.

Effect of fiber misalignment on bending strength of pultruded hybrid polymer matrix composite rods subjected to bending and tension

It is demonstrated that the unusual failure of unidirectional hybrid carbon and glass fiber composite rods under bending and tension can be explained by a combined experimental, analytical, and numerical analysis. To simulate possible transportation, in-service, and installation conditions, ACCC® conductor cores, manufactured by CTC Global,were tested in three- and four-point bending experiments. Axial stresses were predicted analytically and numerically with the likely failure initiating locations identified for rods subjected to bending with applied axial tension. As expected under pure bending, composite rods will fail catastrophically from excessive compressive stress in the carbon composite region. The initiating damage mechanisms will change from compressive to tensile modes as axial tension increases. Natural fiber misalignment must be considered in the failure analysis of composite rods as it can significantly reduce bending strength and influence the locations of damage initiation.

Design and experimental verification of self-supporting topologies for selective laser melting

Self-supporting design is an important issue that needs to be considered in the combination of topology optimization (TO) and additive manufacturing (AM). In this paper, the self-supporting and printable Messerschmitt–Bölkow–Blohm (MBB) beams of Ti6Al4V alloy are designed by combining Solid Isotropic Microstructure with Penalization method (SIMP) with Langelaar's AM filter and manufactured by selective laser melting (SLM). Then the formability and the bending behavior of experiments and simulation for MBB beams are investigated. The results reveal that TO can reduce the structural weight for AM effectively. Moreover, the MBB beams have the best formability when the volume fraction is greater than 0.3. Under bending loads, the overall performance of MBB beams improves with the increase of the volume fraction. Among them, the specific stiffness and comprehensive performance of the variable-section MBB beams (3D, VS-MBB) are superior to those of the constant-section MBB beams (2D, CS-MBB). When the volume fraction is around 0.4, the VS-MBB beams have the best formability and specific stiffness. Furthermore, MBB beams have two failure modes: the failure of the thin rods in the structures, and the crushing failure on the loading position. Finally, the ABAQUS simulation results are consistent with those of experiments within the permissible error evaluation, which will provide potent guidance for future researches.

Safety Analysis of Carbon Fiber Composite Subjected to Different Levels of Bending Moment

Carbon fiber composite rods can be widely employed in engineering due to their high ratio of the strength and density. Carbon fiber composite rods can be only used in the suitable conditions. In particular, under the bending deformation, the failure of carbon fiber composite rods can lead to the engineering accident if the applying bending moment is beyond a certain value. In this paper, a finite element model (FEM) for carbon fiber composite rod was put forward to simulate the mechanical responses of carbon fiber composite rod subjected to bending moment loading. A series of simulations under different levels of bending moments were conducted. Based on the calculated results, the limit bending moment was obtained by comparing the mechanical responses and the failure strength.

Understanding field failures of composite insulators

The failure mechanism of in-service fiber reinforced plastic (FRP) rod used in composite insulators is studied experimentally; the integrity of Electrical/Chemical Resistance (ECR) of glass fibers in an epoxy-resin matrix of FRP rod used in transmission composite insulator is the subject of study. FRP Rods are subjected to extreme conditions of aging: the results of leakage current analysis, physical inspection, and corresponding Fourier Transform Infrared Spectroscopy (FTIR) strongly support the reason for the failure of FRP rods under operating condition. The entry of water inside the rod-silicone rubber interface, accompanied by arcing, rise in temperature cause considerable damage and hence failure in the operation of rods. Some interesting results of laboratory aging/failures are compared with field failure samples, also a laboratory method to evaluate failures of FRP rods is proposed.

High temperature corrosion and metal dusting failure of deflector rods in a petrochemical cracking unit

In this study failure of deflector rods of a cracking unit in a petrochemical plant was investigated. The rods were exposed to harsh carbonaceous/oxidative working condition at high temperature (≈800 °C). Failure of the rods was reported after 40,000 h of operation. Optical examinations indicated a rough surface with severe localized spallation at some locations on the rods. Scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses showed that metal dusting in addition to spallation led to surface deterioration. Hardness profilometry showed a remarkable increase in hardness at exposed surface. Furthermore, tensile test results showed significant reduction in elongation of the failed rods. Loss of ductility in severely carburized rods, had caused brittle fracture during service. Overall it was concluded that metal dusting and oxide scale spallation were the main cause of the failure.

The Comparative Analysis of Antegrade Versus Retrograde Approach for a Failed Porous Tantalum Rod Removal During Conversion to Total Hip Arthroplasty.

BackgroundThe failure of porous tantalum rods applied to patients with osteonecrosis of the femoral head (ONFH) has been increasingly reported during the last few years. Very few studies have reported methods for implant removal. This study aimed at comparing 2 procedures used for the removal of a failed tantalum rod during conversion to total hip arthroplasty (THA).Material/MethodsA total of 65 patients (65 hips), who underwent THA after failed implantation of a tantalum rod between June 2007 and December 2016, were retrospectively evaluated. These patients were classified into 2 groups depending on whether the antegrade approach (removal of the tantalum rod from the tip to the butt at the lateral femoral cortex, n=27) or retrograde approach (removal of the tantalum rod from the butt at the lateral femoral cortex to the proximal tip, n=38) was used for rod extraction. These 2 groups were compared for incision length, operation time, blood loss, fracture, tantalum debris, Harris hip scores, and the presence of osteolysis and/or radiolucency.ResultsThese 2 groups did not present any significant differences in terms of Harris hip score and incision length. However, the operation time (P=0.000), blood loss (P=0.000), amount of tantalum debris (P=0.000), and presence of radiolucency (P=0.046) were greater for the retrograde approach than for the antegrade approach.ConclusionsThe risk of conversion to THA following failed tantalum rod implantation is high. In such cases, the antegrade procedure was found to be a simple and efficient method for removing the trabecular metal rod with the use of a trephine.

In vitro degradation behavior of Mg wire/poly(lactic acid) composite rods prepared by hot pressing and hot drawing

In this study, we prepared Mg wire/poly(lactic acid) composite rods by hot pressing (HP) and hot drawing (HD) processes, which show desirable application potential as a biodegradable implant in orthopedics. The influences of the volume content of Mg wires and processing steps on the degradation behavior of composite rods as well as the mutual influence between Mg and poly(lactic acid) (PLA) during degradation were investigated. During degradation, the improved interface bonding between Mg and PLA by micro-arc oxidation can effectively inhibit the diffusion of the medium from the ends to the central part, supported by XR-CT results, which show the degradation cracks in PLA initiated and propagated along the radial direction of the rod rather than the axial direction. When compared with the hot pressed rod, the three passes hot drawn rod had lower degradation rate and better strength retention during long-time immersion. This is ascribed to the higher crystallinity of the PLA matrix by HD. For both hot pressed and hot drawn rods, more Mg content of the wires will result in an increase in the degradation rate of PLA due to alkaline catalytic hydrolysis. Therefore, we can not only predict the degradation period by the present degradation mathematical model but also further control degradation rate by adjusting processing steps and wire volume content. This will be helpful for future material design and indication selection. Statement of significanceWe investigated the influence of interface microstructure, self-reinforced PLA matrix, and wire volume content on the degradation behavior and clarified the differences in the degradation mechanism of composite rods. The 3D morphology of cracks in composite rods enlightened us a clear understanding about the emergence and evolution of cracks, which revealed the reason for the failure of composite rods. The degradation model can be used to predict the degradation period and provide valuable information for their future application.

Failure analyses and wear mechanisms of rock drill rods, a case study

Rock drill rod failure is a big concern for the mining industry. The tough conditions required to break down rock material into small pieces subject rock drill components to high mechanical stresses and corrosion that lead to the failure of the drill rods. This paper describes a detailed examination of rock drill rods failed during field operations. The drill rods were manufactured from a high strength, hardened and tempered steel 22NiCrMo12-5F, carburized for better surface performance. The examination was carried out by means of light optical microscopy and scanning electron microscope. Microhardness profiles were performed for the studied rods. The focus of the present case study was to characterize the failure mechanisms and surface damages of the failed drill rods. The examined drill rods failed due to the initiation and propagation of fatigue microcracks at the outer surface of the thread. Surface cracks propagated to a certain crack length until the fracture toughness of the drill rod was exceeded and the final failure occurred. Multiple short cracks were observed on the fracture surface of the failed rods. The observed cracks propagated perpendicularly to the impacting direction towards the inner surface of the rods. Two different crack initiation mechanisms were observed in the present study, crack initiation from pits and crack initiation from severe plastic surface deformation. Sliding and abrasive wear damage, severe plastic deformation and pitting corrosion were observed on the threaded portion of the rods. Sliding wear was the most common wear damage mechanism observed in the thread joint. Pitting corrosion and severe plastic deformation, made the worn surface susceptible to crack initiation.

Wednesday, September 26, 2018 7:35 AM–9:00 AM ePosters: P12. The interaction of satellite rod reconstruction, rod material and rod diameter on posterior rod strain in pedicle subtraction osteotomies for adult spinal deformity correction: a finite element analysis

BACKGROUND CONTEXT Pedicle subtraction osteotomy (PSO) is a prevailing technique used to correct adult spinal deformity; however, instrumentation failure of rods remains a significant concern at the PSO level or lumbosacral junction. Several options have been proposed in clinical literature to reduce mechanical demand of the rod, including multirod constructs (three- or four-rod vs. two rods), alternative rod materials [stainless steel (SS) or cobalt chrome (CoCr) vs. titanium (Ti)], or increased rod diameter (6.35 mm vs. 5.5 mm). Nevertheless, a comprehensive evaluation of these construct features is warranted and necessary to guide optimization of post-PSO surgical reconstruction. PURPOSE The current study investigates the effect of multirod techniques, and varied rod material and diameter, on motion-induced rod strain at the PSO and L5-S1. STUDY DESIGN/SETTING Finite element analysis. METHODS A lumbosacral finite element model (T12-S1) was developed and validated with cadaveric range of motion data. Vertebral segments were modeled as three-dimensional solid elements. Intervertebral discs (nucleus and annulus fibrosis) were structured as hyperelastic materials. The intact model underwent PSO at L3, and Ti pedicle screws and rods from T12-S1. Simulations assessed (1) multirod construction, with either a satellite rod on patient left (three-rod) or bilateral four-rod constructs; (2) posterior rod materials (SS or CoCr vs. Ti); and (3) 5.5 mm versus 6.35 mm posterior rods. A pure 10 Nm moment was applied at T12 to simulate flexion–extension. Motion-induced rod strain was normalized to the two-rod construct (100%), averaged between left and right rods, and evaluated at the PSO and L5-S1. RESULTS All rods, irrespective of number of accessory rods, material, or diameter, experienced less strain than two-rod construct across the PSO level and L5-S1. At the PSO, 5.5 mm three-rod Ti, SS, and CoCr constructs reduced primary rod strain to 65%, 41%, and 34%, respectively; 6.35 mm rods reduced strain to 47%, 29%, and 24%, respectively. Similarly, four-rod Ti, SS, and CoCr constructs reduced primary rod strain to 49%, 30%, and 25%, respectively; 6.35 mm rods reduced strain to 35%, 21%, and 17%, respectively. At L5–S1, 5.5 mm three-rod Ti, SS, and CoCr constructs reduced primary rod strain to 82%, 59%, and 51%, respectively; 6.35 mm rods reduced strain to 73%, 48%, and 30%, respectively. Similarly, four-rod Ti, SS, and CoCr constructs reduced primary rod strain to 85%, 60%, and 51%, respectively; 6.35 mm rods reduced strain to 75%, 48%, and 30%, respectively. Some interactions were observed. At the PSO, 6.35 mm three-rod construction was equivalent to 5.5 mm four-rod, across Ti (47% vs. 49%), SS (29% vs. 30%), and CoCr rods (24% vs. 25%). Similarly, at L5-S1, 5.5 mm three- and four-rod constructs were equivalent across Ti (82% vs. 85%), SS (59% vs. 60%), and CoCr rods (51% vs. 51%); similar trends with 6.35 mm rods occurred across Ti (73% vs. 75%), and SS rods (48% vs. 48%). CONCLUSIONS Overall trends in primary rod strain across the PSO and L5-S1 observed in the present study are as follows: (1) four-rod rod strain

Reliability Assessment of the Compressor Connecting Rods

The article presents an analysis of the stress condition of a connecting rod’s small ends. The strains acting in the most stressed section of the connecting rod’s small end are defined experimentally and using the numerical experiment. The probability of the failure of the connecting rods, depending on the acting load and conjunction clearances, is estimated. It is proposed to harden the working surface to increase the probability of a failure-free operation.

Tensile properties of novel carbon/glass hybrid thermoplastic composite rods under static and fatigue loading

ABSTRACT Novel carbon/glass hybrid thermoplastic composite rods have been developed consisting of a PAN-based carbon fiber, an E-glass fiber, and a thermoplastic matrix. Three types of hybrid rods with different carbon/glass ratios were then fabricated. The surface and cross-sectional morphologies of the hybrid rods were observed using a digital microscope. Additionally, the volume fractions of carbon/glass fibers, matrix, and void were determined by specific gravity measurements and thermogravimetric analyzes. The glass fibers in the hybrid rods display a braided structure of the 2/2 twill weave. The braid angle (defined as the orientation angle of the interlacing yarns with respect to the longitudinal axis of the rod) ranged from 22.3° to 35.2°. The various volume fractions were in the ranges of 24.6-46.2% for the carbon fiber, 23.2-39.8% for the glass fiber, 23.4-25.5% for the matrix, and 7.3-10.2% for the voids. The tensile properties and fracture behavior of the hybrid rods under static and fatigue loading were also investigated. For the static tests, the stress applied to the specimen was nearly linearly proportional to the strain until the failure of all-hybrid rods. The tensile modulus, strength, and failure strain of the hybrid rods were measured in the ranges of 65-91GPa, 1.42-1.84 GPa, and 2.1-2.2%, respectively. The tensile modulus and strength increased as the volume fraction of the carbon fiber increased. However, the failure strain decreased as the volume fraction of the carbon fiber increased. For fatigue tests, the maximum applied stress-number of cycles to failure (S-N) curves for all-hybrid rods were obtained from 0.1 of the stress ratio (minimum/maximum stress) and 10 Hz of the loading frequency. The fatigue strength at 107 cycles for all-hybrid rods was less than 30% of ultimate breaking stress. The fatigue performance of the hybrid rods was significantly lower than that of conventional carbon fiber reinforced polymer matrix composites and steel rods. The voids in the hybrid rods affected the fatigue tensile properties.