Preliminary Finite Element Analysis Research Articles

Derivation, parameterization and validation of a creep deformation/rupture material constitutive model for SiC/SiC ceramic-matrix composites (CMCs)

The present work deals with the development of material constitutive models for creep-deformation and creep-rupture of SiC/SiC ceramic-matrix composites (CMCs) under general three-dimensional stress states. The models derived are aimed for use in finite element analyses of the performance, durability and reliability of CMC turbine blades used in gas-turbine engines. Towards that end, one set of available experimental data pertaining to the effect of stress magnitude and temperature on the time-dependent creep deformation and rupture, available in the open literature, is used to derive and parameterize material constitutive models for creep-deformation and creep-rupture. The two models derived are validated by using additional experimental data, also available in the open literature. To enable the use of the newly-developed CMC creep-deformation and creep-rupture models within a structural finite-element framework, the models are implemented in a user-material subroutine which can be readily linked with a finite-element program/solver. In this way, the performance and reliability of CMC components used in high-temperature high-stress applications, such as those encountered in gas-turbine engines can be investigated computationally. Results of a preliminary finite-element analysis concerning the creep-deformation-induced contact between a gas-turbine engine blade and the shroud are presented and briefly discussed in the last portion of the paper. In this analysis, it is assumed that: (a) the blade is made of the SiC/SiC CMC; and (b) the creep-deformation behavior of the SiC/SiC CMC can be represented by the creep-deformation model developed in the present work.

SU-F-207-05: Excess Heat Corrections in a Prototype Calorimeter for Direct Realization of CT Absorbed Dose to Phantom

Purpose: To reconcile air kerma and calorimetry measurements in a prototype calorimeter for obtaining absorbed dose in diagnostic CT beams. While corrections for thermal artifacts are routine and generally small in calorimetry of radiotherapy beams, large differences in relative stopping powers of calorimeter materials at the lower energies typical of CT beams greatly magnify their effects. Work-to-date on the problem attempts to reconcile laboratory measurements with modeling output from Monte Carlo and finite-element analysis of heat transfer. Methods: Small thermistor beads were embedded in a polystyrene (PS) core element of 1 cm diameter, which was inserted into a cylindrical HDPE phantom of 30 cm diameter and subjected to radiation in a diagnostic CT x-ray imaging system. Resistance changes in the thermistors due to radiation heating were monitored via lock-in amplifier. Multiple 3-second exposures were recorded at 8 different dose-rates from the CT system, and least-squares fits to experimental data were compared to an expected thermal response obtained by finite-element analysis incorporating source terms based on semi-empirical modeling and Monte Carlo simulation. Results: Experimental waveforms exhibited large thermal artifacts with fast time constants, associated with excess heat in wires and glass, and smaller steps attributable to radiation heating of the core material. Preliminary finite-element analysis follows the transient component of the signal qualitatively, but predicts a slower decay of temperature spikes. This was supplemented by non-linear least-squares fits incorporating semi-empirical formulae for heat transfer, which were used to obtain dose-to-PS in reasonable agreement with the output of Monte Carlo calculations that converts air kerma to absorbed dose. Conclusion: Discrepancies between the finite-element analysis and our experimental data testify to the very significant heat transfer correction required for absorbed dose calorimetry of diagnostic CT beams. The results obtained here are being used to refine both simulations and design of calorimeter core components.

Finite Element Simulation of Stable Fatigue Crack Growth Using Critical CTOD Determined by Preliminary Finite Element Analysis

Finite element simulation of stable fatigue crack growth using critical crack tip opening displacement (CTOD) was done. In the preliminary finite element simulation without crack growth, the critical CTOD was determined by monitoring the ratio between the displacement increments at the nodes above the crack tip and behind the crack tip in the neighborhood of the crack tip. The critical CTOD was determined as the vertical displacement at the node on the crack surface just behind the crack tip at the maximum ratio. In the main finite element simulation with crack growth, the crack growth rate with respect to the effective stress intensity factor range considering crack closure yielded more consistent result. The exponents m in the Paris law were determined.

Preliminary modelling of the saturation of a full-sized clay and concrete shaft seal

Abstract A shaft seal was installed at the intersection of the 5 m-diameter access shaft of the Atomic Energy of Canada Limited's Underground Research Laboratory with a major, moderately dipping fracture zone (FZ) to limit the mixing of the saline groundwater at the zone below the FZ with freshwater at the zone above the FZ. The shaft seal consists of 6 m-thick clay-based material that is sandwiched between 3 m-thick upper and lower concrete components, and its centre is located at c. 273 m depth below the surface. This paper presents the results of preliminary finite element analyses using 2D-axisymetric and 3D geometries simulating the saturation of the shaft seal. The components in the analyses include the clay, concrete, intact rock and FZ. Of particular interest are the field-observed differences in the hydraulic pressures above and below the shaft seal. The results of the numerical analyses were compared with the 3-year monitoring data. The results of the numerical models showed that the decrease in the pressure difference indicates that there was flow path that connects the zones above and below the shaft seal. A preliminary long-term estimation of the shaft seal hydraulic response (up to 1000 years) was done based on the hydraulic pressure and excavation volume data, combined with the assumptions that that the groundwater level will eventually recover to the initial conditions.

Experimental study of seismic performance of base-isolated frames with U-shaped hysteretic energy-dissipating devices

This study experimentally investigates the seismic performance of base-isolated structures using shake table tests. The base isolating system used in this study consists of laminated rubber bearings and U-shaped hysteretic energy-dissipating devices called UH dampers below. UH dampers used for a base-isolated structure experience significantly large deformations in both lateral directions when subjected to severe ground shaking. In order to accommodate such large deformations without noticeable strength degradation, UH dampers have been made of high toughness steel (HTS) that possesses excellent material properties compared to ordinary structural steel (SS). Based on preliminary finite element analyses, UH dampers employing slotted-hole details to induce uniform stress distribution are proposed. Also, the analyses of UH dampers with slotted-hole details suggests that they could be made of SS instead of relatively expensive HTS. Prior to the shake table tests, component cyclic tests of a laminated rubber bearing and the proposed UH dampers made of HTS and SS were performed to determine their structural characteristics. Base-isolated structures for shake table tests were initially designed based on the component test results and the equivalent lateral force procedure. Three shake table test specimens (a fixed-base structure, a base-isolated structure with UH dampers made of HTS (UH-H dampers), and base-isolated structure with slotted UH dampers made of SS (UH-S dampers)) were prepared. The shake table tests were performed with historical earthquake records. The shake table test results show that the base-isolated specimens with UH dampers achieved better seismic response compared to the fixed-base frame. In addition, the UH-S dampers present a seismic response that is comparable to the UH-H damper.

Evaluation of in-plane ply shear properties from unidirectional plate torsion tests

Torsion tests were conducted on unidirectional carbon/epoxy laminated plates. Preliminary finite element analyses showed that the specimen geometry selected avoided pronounced geometric non-linearity and ensured that a significant volume of material would be under a high fraction of the maximum shear stress. Furthermore, the clear prevalence of in-plane shear stresses allowed the development of a simplified data analysis model. Calculated shear-stress strain curves were consistent with the results of tensile tests on angle-ply coupons, despite lower failure stresses that may have been caused by surface defects or by spurious transverse tensile stresses. Nevertheless, the unidirectional plate torsion test is worthy of further research, given the structural relevance of torsional loads and the problems of in-plane shear tests methods.

Blast injuries to the human mandible: Development of a finite element model and a preliminary finite element analysis

ObjectiveIn an attempt to explore new tools for constructing a model of blast injuries to the human mandible, a finite element method was used. This model allowed us to perform dynamic simulations and analyse the injury processes and severity of trauma to the human mandible from an explosion striking at the middle mandibular angle. MethodsA 3D finite element model of the human mandible was created using digitally visualised CT scanning data of the human mandible. It was used to dynamically simulate the complete injury process of a blast event to a human mandible (at the middle mandibular angle) under the injury conditions of a 600mg TNT explosion. The model was also used to elucidate the subsequent mandibular damage and the dynamic distribution of several biomechanical indices (e.g., stress, and strain). The resulting data were subjected to a comparative analysis. ResultsSimulation was successfully conducted for injury events in which 600mg of TNT exploded at 3cm, 5cm and 10cm from the middle mandibular angle of a human mandible; specifically, the simulation included the dynamic injury processes and the distribution of stress and strain in various parts of the damaged mandible. A comparison of the simulation data revealed that different blast distances resulted in considerable variation in the severity and biological indices of the mandibular injury. ConclusionThe finite element model was able to dynamically simulate the blast-initiated trauma processes to a human mandible, which allowed for investigation of the severity of damage to the mandible under different injury conditions. This model and the simulation method are conducive for applications in basic studies and clinical investigations of blast-initiated injury mechanisms of bone tissues.

Integrated geological-architectural pilot study of the Biet Gabriel-Rufael rock hewn church in Lalibela, northern Ethiopia

We present a geological and architectural integrated pilot study, aiming at the preservation of the Biet Gabriel-Rufael church, located in Lalibela, the worldwide known Ethiopian rock hewn monumental site protected by UNESCO since 1978. The town developed since the Neolithic up to the medieval age, as inferred from the traces of three distinct architectural phases. Lalibela was built on a geological substratum made of rocks belonging to the Ethiopian Plateau suite, which is mainly composed of basalts of fissural origin or derived from shield volcanoes. The geological units are composed of alternating massive and scoriaceous basalts. The main scoriaceous basalt level, embedded within the massive basalts, is 30–40 m thick and corresponds to the horizon within which the Biet Gabriel-Rufael church all the other monuments of Lalibela have been carved. Therefore, the evolution of the town was strongly conditioned by the occurrence and extent of the softer scoriaceous basalt level. Many fracture systems of both natural (i.e. geological) and anthropic origin (these latter connected to the carving of the church), were recognized. The fracture pattern determined the subdivision of the church into different blocks that can behave independently, thus compromising the stability of the monument. A net of deformometers and fracture gauges was installed for the monitoring of the fracture system and a preliminary Finite Element analysis, following the approach used for underground excavations, was performed, with the aim of elucidate the mechanical behaviour of the rock. The integration between geo-mechanical approach to the rock mass and the architectural study of the critical situation due to the carving and connected to buildings, resulted in the precise individuation of future interventions devoted to the conservation of these monuments.

The Minnesota inverted-tee system: Parametric studies for preliminary design

The precast concrete inverted-tee system was adopted by the Minnesota Department of Transportation after the 2004 FHWA/AASHTO International Scan Tour of bridge rapid construction techniques in Europe and Japan. As of 2005, two bridges were built in Minnesota adapting the Poutre-Dalle system developed in France. One of the two bridges, the Center City Bridge (MN bridge 13004), has been monitored for transverse load distribution and continuity over the pier since the deck was cast in September 2005. In addition, a two-span specimen was constructed to investigate different parameters, such as flange thickness, bursting rein- forcement, horizontal shear reinforcement, and flange surface treatment. One of the four precast concrete sec- tions of the laboratory specimen was identical to those used for MN bridge 13004. Part of the investigation was conducted to optimize section design through a parametric study. In addition, preliminary linear elastic finite element analyses were conducted to simulate the behavior of the system. The finite element models were calibrated using results obtained from static tests of MN bridge 13004 and the laboratory specimen. This paper presents a series of considerations obtained from a preliminary parametric study on different span lengths and bridge configurations. It also discusses some matters that had to be resolved to obtain ac- ceptable agreement between experimental results and analytical approach. For all of the cases investigated, the service stresses were found to control the design.

Investigations about the Single Point Incremental Forming of Anisotropic Titanium Alloy Sheets

The present work focuses the attention on the Single Point Incremental Forming (SPIF) of the Titanium (Ti) alloy Ti-6Al-4V. Tensile tests were carried out using the optical strain measurement system Aramis3D, in order to determine the mechanical behaviour of the alloy and to investigate the anisotropy of such alloy. Finite Element (FE) simulations of the SPIF process (using ABAQUS/explicit) were performed using a simple but non-axialsymmetric shape (truncated pyramid) with the aim of investigating the effect of both the tool/pitch ratio (D/p) and the draw angle (α), taking into account the anisotropic behaviour. The analysis of plastic strains and thinning maps, together with the evaluation of shape errors originated by the forming process, highlighted that the parameter D/p plays a key role in the SPIF. Results from the preliminary FE analysis were used for investigating the production by SPIF of an automotive component (car door shell). A specific subroutine was created by the authors for automatically generating the tool path to be used in both the FE simulations and the manufacturing of parts by SPIF on a CNC milling machine.

Dynamic simulation and preliminary finite element analysis of gunshot wounds to the human mandible

ObjectiveDue to the complications arising from gunshot wounds to the maxillofacial region, traditional models of gunshot wounds cannot meet our research needs. In this study, we established a finite element model and conducted preliminary simulation and analysis to determine the injury mechanism and degree of damage for gunshot wounds to the human mandible. MethodsBased on a previously developed modelling method that used animal experiments and internal parameters, digital computed tomography data for the human mandible were used to establish a three-dimensional finite element model of the human mandible. The mechanism by which a gunshot injures the mandible was dynamically simulated under different shot conditions. First, the residual velocities of the shootings using different projectiles at varying entry angles and impact velocities were calculated. Second, the energy losses of the projectiles and the rates of energy loss after exiting the mandible were calculated. Finally, the data were compared and analysed. ResultsThe dynamic processes involved in gunshot wounds to the human mandible were successfully simulated using two projectiles, three impact velocities, and three entry angles. The stress distributions in different parts of mandible after injury were also simulated. Based on the computation and analysis of the modelling data, we found that the injury severity of the mandible and the injury efficiency of the projectiles differ under different injury conditions. ConclusionsThe finite element model has many advantages for the analysis of ballistic wounds, and is expected to become an improved model for studying maxillofacial gunshot wounds.

Preliminary Finite Element Analysis of Shot Peening for Austenitic Stainless Steels

In this study, the preliminary finite element analysis of shot peening was carried out in order to investigate the fundamental mechanism of shot peening for stainless steels. For numerical simulations with high-rate deformation such as shot peening, rate-dependence plasticity models are necessary to get better analysis results. Therefore the stress-strain relation at high-strain rates of austenitic stainless steels were obtained by split Hopkinson pressure bar (SHPB) tests. The parameters of Johnson-Cook plasticity model were determined from the result, and then the finite element analysis of shot peening was carried out using the parameters. Consequently, the compressive residual stress was created beneath the surface of the target but was changed to the tensile residual stress with an increase in the depth.

Reassessment of Scottish and Southern Energy dams for PMF conditions

Since 2003, Halcrow Group has carried out seismic and, where appropriate, probable maximum flood (PMF) stability analyses on all Scottish and Southern Energy's dams in Scotland. Initial screening studies identified a number of concrete gravity dams where conventional stability and preliminary finite-element analyses indicated potential instability under PMF conditions. This paper describes a range of different approaches taken to address these issues, including hydrological reassessment, more sophisticated structural analysis and foundation anchoring. Development of evacuation plans is also under consideration for one intractable case.

Wound ballistics of the pig mandibular angle: A preliminary finite element analysis and experimental study

To study wound ballistics of the mandibular angle, a combined hexahedral-tetrahedral finite element (FE) model of the pig mandible was developed to simulate ballistic impact. An experimental study was carried out by measuring impact load parameters from 14 fresh pig mandibles that were shot at the mandibular angle by a standard 7.62 mm M43 bullet. FE analysis was executed through the LS-DYNA code under impact loads similar to those obtained from the experimental study. The resulting residual velocity, the transferred energy from the bullet to the mandible, and the surface area of the entrance wound had no statistical differences between the FE simulation and the experimental study. However, the mean surface area of the exit wounds in the experimental study was significantly larger than that in the simulation. According to the FE analysis, the stress concentrated zones were mainly located at the region of impact, condylar neck, coronoid process and mandibular body. The simulation results also indicated that trabecular bone had less stress concentration and a lower speed of stress propagation compared with cortical bone. The FE model is appropriate and conforms to the basic principles of wound ballistics. This modeling system will be helpful for further investigations of the biomechanical mechanisms of wound ballistics.

粒界き裂に基づく単一鉱物多結晶岩石の一軸引張破壊解析

Using joint elements for a mechanical model of grain boundaries, we performed a preliminary 3D finite element analysis of uniaxial tensile fracture for specimen models of monomineral polycrystalline rock under the assumption that fracturing occurs only at the grain boundaries. The specimen models were created on a computer by the method previously proposed by the authors, and the constitutive law of the grain boundaries was derived by applying the associated flow rule in the plastic theory and a tension-shear-softening curve to an extended Coulomb criterion. Tensile fracturing initiates at grain boundaries with a small angle of the normal direction relative to the loading axis, which are followed by grain boundaries with a larger angle of the normal direction. Unloading of intergranular cracks occurs before the peak strength when the intergranular cracks do not compose the final failure plane that is completely formed near the inflection point of the axial stress-axial strain curve after the peak. During the completion of the final failure plane, the conversion of failure mode from tension to shear occurs at intergranular cracks that have a large angle of the normal direction relative to the loading axis. For these intergranular cracks, the axial displacement given at an end of the specimen is converted to a shear displacement, rather than an opening displacement, and the normal stress becomes to be compressive due to shear dilation. Furthermore, the number of tensile intergranular fracturing at the peak strength increases with a decrease in the constant α that characterizes the rate of decrease in the tensile strength in the tension-shear-softening curve of the grain boundaries, and as a result, the tensile strength of the rock specimen increases with a decrease in the constant α. However, the effect of the residual frictional coefficient is small and limited to the stage after the final failure plane is completely formed, since the residual friction coefficient affects the mechanical behavior of the grain boundaries only after the failure plane is completely formed.

Reduced Link Sections for Improving the Ductility of Eccentrically Braced Frame Link-to-Column Connections

Eccentrically braced frames (EBFs) are desirable seismic load resisting systems as they combine the high elastic stiffness of concentrically braced frames with the ductility and stable energy dissipation of moment resisting frames. EBFs with links attached to the columns are particularly appealing for architectural flexibility as they provide multiple locations for placement of doors and hallways. However, previous research has shown that link-to-column connections are prone to failure at low drift levels, due to their susceptibility to fracture at the link flange-to-column welds. This paper investigates the application of the reduced beam section concept for links in eccentrically braced frames to enhance the ductility of link-to-column connections. A design procedure for link section reduction is proposed and preliminary finite-element analyses are conducted on a shear link with various reduced section geometries. A parametric study performed on an array of links having various cross sections and lengths suggests that the reduced link section may substantially reduce the plastic flange strains at the link ends, which can improve the fracture life. The reduction in plastic flange strains is found to be significant for all links, with larger reductions for intermediate and flexural links. Furthermore, the detrimental kinking deformation of the flanges, caused by the large rotation demands in shear links, is moved away from the column face when reduced sections were used. While the analysis results show promise, experimental verification is recommended before the proposed design procedure can be implemented in practice.

Class A Prediction of the Behavior of Soft Estuarine Soil Foundation Stabilized by Short Vertical Drains beneath a Rail Track

In Australia, very few rail tracks have been constructed directly on deep estuarine deposits. In recent years, Kooragang Island has become a major export terminal and most coal trains need to cross the main lines at Sandgate to enter Kooragang Island. In this study, a rail track built on up to 30 m of thick soft estuarine soil was stabilized with relatively short vertical drains to consolidate the soil just beneath the track, and no additional preloading surcharge was provided, except the weight from the trains. The initial soil compression was caused by the passage of trains with a speed restricted at 40 km/h. From this study, it is shown that prefabricated vertical drains significantly decrease the buildup of excess pore-water pressure during cyclic loading, and also continue to dissipate excess pore-water pressure during the rest period. A preliminary finite-element analysis was employed to examine the performance of vertical drains, and a Class A prediction was obtained in terms of lateral and vertical displacements. The monitored settlement and lateral displacement results are presented and discussed. The study shows that relatively short vertical drains are sufficient for providing stability for rail tracks, without the need for driving deep vertical drains through the entire soft soil depth.

Investigating the potential advantages of a new design metacarpophalangeal joint

This paper investigates a new metacarpophalangeal joint design aimed at treating patients with moderate to severe forms of arthritis affecting the index, long, ring, and little fingers. Current small joint arthroplasty designs, including those for the metacarpophalangeal joint of the hand, have had limited success owing to mechanical failures and can be divided into two main families: single-piece elastomer implants and surface articulating implants. The design proposed in this study involves combining the principles of a surface weight-bearing articulating implant with those of a spanning elastomeric implant. The design consists of metacarpal and proximal phalangeal articulating housings and a central flexible spanning elastomer rod that maintains the alignment of the metacarpal and proximal phalangeal components. A preliminary finite element analysis was used to investigate the stresses in the design, the wear of the articulating bearing surfaces for different material combinations, and the stresses between the central elastomer rod and the articulating housings. This preliminary analysis shows that the design should withstand the probable loading conditions experienced within the human body and that the wear rates of the articulating surfaces and the central elastomer are acceptable.

Uniaxial Tensile and Simple Shear Behavior of Resistance Spot-Welded Dual-Phase Steel Joints

Small test coupons were machined from single spot welds in a dual-phase steel (DP600) to investigate deformation and failure of weld joints in both tension and shear. Quasi-static ( $$ \ifmmode\expandafter\dot\else\expandafter\.\fi{\upvarepsilon } \sim 10^{{ - 4}} \,1/{\text{s}} $$ ) testing was conducted in a miniature tensile stage with a custom image acquisition system. Strain accumulation in each weld was analyzed where fracture occurred, which was typically outside the fusion zone. A few shear test coupons that failed in the fusion zone were found to have the same spheroidal defects noted in previous work, and thus, severely limited weld strength and ductility. A novel strain mapping method based upon digital image correlation was employed to generate two-dimensional deformation maps, from which local stress-strain curves to failure were computed. As an important first step toward incorporation of material models into weld simulations, a preliminary finite element analysis of a tension test successfully reproduced the experimental results with material models for the base, heat-affected, and fusion zone materials generated from prior work.

Effect of Orifice Shape in Contour Crafting with Ceramic Material: A Simulation for Extrusion and Deposition Mechanism

This paper presents our experimentation and modeling efforts to study the pattern of material flow in the extrusion and deposition stages of the Contour Crafting (CC) process. Specifically, we performed a preliminary finite element analysis (FEA) of extrusion and deposition mechanisms with clay as the fabrication material. Using the FEA simulations, we derived certain basic understandings of the effect of extrusion orifice geometry on the performance of CC. We found that a square orifice is most aptly suited, both in terms of delivering the optimal fusion between layers as well as creating the desired external surface profile. Our experiments validate these results.