Types Of Loading Conditions Research Articles

On the fracture possibility of thin-walled tubes under axial crushing

Thin-walled tubes are widely used as energy absorption components in vehicle crashworthiness design where axial crushing is one of the most typical loading conditions. Lightweight materials such as high-strength steel, aluminum and magnesium have been applied for thin-walled tubes for weight reduction. Meanwhile, most of these lightweight materials are more brittle and easily fractured than traditional steel. Distribution and history of stress triaxiality and equivalent strain in the thin-walled tubes under axial crushing have been analyzed in this article with finite element simulation, as these two parameters of stress and strain states are commonly used for constructing fracture locus of materials. It is observed that both stress triaxiality and equivalent strain are transferring along the tube length like waves. Analysis results show that fracture is more likely to take place on the edge than the other positions of square thin-walled tubes. For identical axial crushing stroke, there is little difference of stress and strain states inside the square thin-walled tubes with initial impact velocity varying from 6m/s to 24m/s. Influence of geometrical parameters on the stress and strain states have also been analyzed, including the shape of cross-section corner, the wall thickness and the shape of cross-section, respectively. Analysis results in this article may offer references for design of thin-walled tubes and the necessary experimental characterization of mechanical properties for lightweight materials.

Tribological conditions in mobile bearing total knee prostheses

This paper describes the in-vivo contact conditions that occur in total knee prostheses, with focus on mobile bearing designs. As background, typical loading and kinematic conditions occurring in the human knee joint are briefly reviewed, for normal walking as well as for other activities including running/jogging. The loads and relative motions are then used, along with typical properties of knee joint's synovial fluid, in a transient elastohydrodynamic analysis of the fluid film lubrication conditions at the articulating tibio-femoral interface of mobile bearing total knee prostheses. Most of the analyses in this paper are for the most common material combination used in total knee prostheses, cobalt–chrome–molybdenum femoral component in contact with ultra-high molecular weight polyethylene (UHMWPE) tibial bearing. The transient fluid film thickness and the pressure within the contact area on the implanted knee prostheses are determined during typical walking and jogging cycles. It is found that the lubricating film is so thin that the contact is within the mixed lubrication condition much of the time, and at times descends into the boundary lubrication zone. Therefore, wear of the contacting materials, particularly the UHMWPE, is expected to occur nearly continuously. Examination of retrieved mobile tibial bearings confirmed that wear of the articular bearing surfaces is consistent with predicted contact conditions; wear is most severe where contact pressure is highest and lubricant film thickness is lowest. The effects of different prosthesis materials (e.g., ceramic femoral component) on the resulting minimum film thickness and pressure are determined and the implications for implant wear are discussed.

Performance study of a constant temperature and humidity air-conditioning system with temperature and humidity independent control device

To reduce the large energy penalty for constant temperature and humidity control in conventional air-conditioning systems, a novel temperature and humidity independent control (THIC) device is developed for typical cooling coils. The working principle of the THIC device is to adjust the chilled water flow rate in a cooling coil (CC) to maintain constant temperature and to adjust the apparatus dew point temperature of the CC to maintain constant humidity. A split-range control strategy is developed to control the cooling coil with the THIC device, the heater and the humidifier to achieve reliable control of indoor temperature and humidity while minimizing energy use.Control performance of the THIC device was tested in an existing constant temperature and humidity air conditioning system serving a storeroom in a museum. The field test shows that the indoor temperature and humidity were well controlled in the required range. Energy performance of the THIC was tested using simulation tests on TRNSYS platform. Seven testing cases with different typical load conditions were conducted. The energy performance of the THIC is compared with conventional air conditioning systems. The results show that the THIC device can achieve power saving of 30–50%.

Coupled Thermomechanical Fatigue Tests for Simulating Load Conditions in Cooled Turbine Parts

Modern heavy-duty gas turbines operate under hot gas temperatures that are much higher than the temperature capability of nickel superalloys. For that reason, advanced cooling technology is applied for reducing the metal temperature to an acceptable level. Highly cooled components, however, are characterized by large thermal gradients resulting in inhomogeneous temperature fields and complex thermomechanical load conditions. In particular, the different rates of stress relaxation due to the different metal temperatures on hot gas and cooling air exposed surfaces lead to load redistributions in cooled structures, which have to be considered in the lifetime prediction methodology. In this context, the paper describes coupled thermomechanical fatigue (CTMF) tests for simultaneously simulating load conditions on hot and cold surfaces of cooled turbine parts (Beck et al., 2001, “Experimental Analysis of the Interaction of Hot and Cold Volume Elements During Thermal Fatigue of Cooled Components Made From AISI 316 L Steel,” Z. Metallkunde, 92, pp. 875–881 and Rau et al., 2003, “Isothermal Thermo-mechanical and Complex Thermo-mechanical Fatigue Tests on AISI 316 L Steel—A Critical Evaluation,” Mater. Sci. Eng., A345, pp. 309–318). In contrary to standard thermomechanical fatigue (TMF) testing methods, CTMF tests involve the interaction between hot and cold regions of the parts and thus more closely simulates the material behavior in cooled gas turbine structures. The paper describes the methodology of CTMF tests and their application to typical load conditions in cooled gas turbine parts. Experimental results are compared with numerical predictions showing the advantages of the proposed testing method.

Validation of FE Micromotions and Strains Around a Press-Fit Cup: Introducing a New Micromotion Measuring Technique

Finite element (FE) analysis provides an useful tool with which to analyze the potential performance of implantations in a variety of surgical, patient and design scenarios. To enable the use of FE analysis in the investigation of such implants, models must be experimentally validated. Validation of a pelvic model with an implanted press-fit cup in terms of micromotion and strain is presented here. A new method of micromotion has been introduced to better describe the overall movement of the cup within the pelvis. The method uses a digitizing arm to monitor the relative movement between markers on the cup and the surrounding acetabulum. FE analysis was used to replicate an experimental set up using a synthetic hemi-pelvis with a press-fitted all-metal cup, subject to the maximum loading observed during normal walking. The work presented here has confirmed the ability of FE models to accurately describe the mechanical performance of the press-fitted acetabulum and surrounding bone under typical loading conditions in terms of micromotion and strain distribution, but has demonstrated limitations in its ability to predict numerical micromotion values. A promising digitizing technique for measuring acetabular micromotions has also been introduced.

GE2-2 Laser-Induced Fluorescence to Visualize Gas Mixture Formation in an Optically Accessible Hydrogen Engine(GE: Gas Engine,General Session Papers)

The established tracer laser-induced fluorescence (LIF) technique was newly adapted for the quantitative visualization of hydrogen inside an optically accessible hydrogen engine to investigate the processes of hydrogen-injection, mixture formation, ignition and combustion at motor-relevant operating points. Trimethylamine (TMA) has been seeded to the hydrogen and was thus used as a tracer for hydrogen when applying the LIF technique. End of injection (EOI) was varied at a constant speed of 2000 rpm and a load of 2 bar (IMEP) which represents typical part load condition. The results visualize the influence of EOI on the mixture formation, ignition and the beginning of combustion. The comparison of the visual results of four operating points shows how long it takes even in the case of hydrogen to get a homogeneous mixture at spark timing. Additionally, conventional engine data such as cylinder pressure, temperature, consumption, emissions etc. have been measured. Rough running engine due to uneven distribution in the region of the spark plug could be explained by single-shot images.

Closure to “Discussion of ‘Yield Function for Solder Elastoviscoplastic Modeling’” (2005, ASME J. Electron. Packag., 127, pp. 147–156)

Closure to “Discussion of ‘Yield Function for Solder Elastoviscoplastic Modeling’” (2005, ASME J. Electron. Packag., 127, pp. 147–156)

Loading profile of topotecan into polyvinyl alcohol microspheres (DC Bead™) over a 7-day period

DC Bead™ is successfully used for chemoembolization of various liver cancers. The purpose of this study was to determine the loading capacity of the semi-synthetic topoisomerase-1 inhibitor topotecan into the DC Bead™ microspheres under static or agitated conditions and to assess the physicochemical stability over a period of 7 days. Commercially available topotecan hydrochloride powder (Hycamtin®) was reconstituted with water for injection to yield a nominal concentration of 1 mg/mL topotecan. Polyvinyl alcohol (PVA)-based microspheres (DC Bead™, 300-500 µm, 2 mL/vial) were mixed with 4 mL of the reconstituted topotecan solution. Vials were stored light protected at room temperature under static or agitated conditions for 7 days (n = 3, for each loading condition). At different time intervals, samples were taken from the excess solution and assayed via a stability-indicating HPLC assay. Drug-loading profiles were determined by measuring the remaining topotecan concentration in the excess solution. Under agitated conditions, topotecan was loaded into the microspheres rapidly after mixing. After 5 min 86.4 ± 0.1% of topotecan was loaded. Under static conditions, drug uptake was slower. Only 65.0 ± 0% were loaded after 5 min; 86.6 ± 0.1% drug uptake was achieved not until 1 h. Over a storage period of 7 days, topotecan remained loaded in the DC Bead™ microspheres at a level of >90%. Drug uptake of 4 mg topotecan (1 mg/mL solution) into DC Beads™ was faster under agitated loading conditions. Nevertheless, after 1 h, ∼90% of topotecan was loaded into the DC Bead™ microspheres independent from the type of loading condition. The loading rate remained >90% over the observation period of 7 days and light-protected storage at room temperature. Loading and stability of topotecan-loaded DC Beads™ is suitable and convenient for preparation in a pharmacy-based cytotoxic preparation unit.

Influence of Dispersion and Alignment of Nanotubes on the Strength and Elasticity of Carbon Nanotubes Reinforced Composites

In this paper, the effective strength and elastic properties of carbon nanotube reinforced composites are evaluated using a representative volume element with a number of carbon nanotubes embedded in the matrix. This concept is used to predict the mechanical properties of multiple, unidirectional, aligned, and also randomly dispersed carbon nanotube reinforced composites. To characterize these nanocomposites, a continuum model has been developed for large-scale analysis. The effective Young’s and shear moduli of the composites are determined using finite element analysis under the effect of elastic deformation. The role of design parameters like length and volume fraction of carbon nanotubes, tensile and shear strength as well as type of loading conditions are analyzed for multiple carbon nanotubes based composites. The discontinuous and continuous types of carbon nanotubes, with aligned and random distribution, are evaluated. The results show that the continuous and aligned carbon nanotubes produce the largest tensile modulus, compared to the discontinuous and aligned as well as discontinuous and randomly oriented carbon nanotubes along the longitudinal direction.

The Analysis on Structure of U-Shaped Compartment Based on Soil Mechanics Principle

According to the project requirements, U-shaped compartment was designed and analysed based on soil mechanics principle. The finite element models of U-shaped compartment structure were established, shell element was employed to mesh compartment. Analysis on the structure of the compartment against typical loading conditions was carried out to get the stress distribution of the compartment structure.

Numerical Analysis of Ship Wave Loads and Structure Strengthen Analysis on a Wind Power Installation Ship

In a typical load condition of wind power equipment Installation ship, using the three-dimensional potential flow theory to prediction the long-term response of wave induced loads. then using the main load control parameters as a basis for the design wave selection, then application of DNV's SESTRA program make the wave-induced directly to the structure to finite element simulation. The results show that the hull structural design can meet the requirements.

Evolution of the crystal stress distributions in face-centered cubic polycrystals subjected to cyclic loading

Due to the heterogeneous nature of polycrystalline metals, the stress distribution at the crystal level is influenced by the complex interplay of factors such as the orientations of the crystal lattices, the elastic and plastic mechanical properties, the interactions between neighboring crystals, and the type of loading conditions. In this paper, we investigate the evolution of the crystal scale stress and elastic strain distributions under cyclic loading. More specifically, we examine the orientation dependent lattice strains in face-centered cubic polycrystals under fully reversed, strain-controlled cyclic loading using a cyclic hardening model implemented within a crystal-based finite element formulation. The directional strength-to-stiffness ratio and the single crystal yield surface (SCYS) topology are used to provide a quantitative explanation of the observed hysteresis behavior when the lattice strains are plotted as a function of the macroscopic stress. The directional strength-to-stiffness ratio influences the progression of yielding in the elastic–plastic transition regime, leading to a nonlinear response in the elastic–plastic transition regime and causing hysteresis behavior in the macroscopic stress versus lattice strain curves. The lattice strains after the elastic–plastic transition regime are influenced by the single crystal elastic moduli and the facet/vertex attributes of the SCYS. We found that the same trends hold in the absence of slip system hardening and in the presence of a strong rolling texture.

Assessment of the DCLL TBM Thermostructural Response Based on ITER Design Criteria

The U.S. Dual Coolant Lead Lithium (DCLL) ITER Test Blanket Module (TBM) is under development for operation in the ITER reactor. The DCLL TBM must satisfy the Structural Design Criteria for ITER In-vessel Components (SDC-IC), which provides rules for the design evaluation and stress analyses of in-vessel mechanical components of ITER with the purpose of ensuring that required safety margins are maintained relative to the types of mechanical damage which might occur as a result of imposed loadings.Primary stresses on the blanket structure come from the pressurization of coolants, the weight of the blanket element, and any electromagnetic forces due to plasma disruptions events. Secondary stresses in the materials due to thermal stress resulting from temperature gradients also contribute to the stress state of the structure. The response to primary stresses will depend on the distribution of loads, the blanket support, as well as material thermo-physical properties, which depend on operating temperatures, loads, fabrication and heat treatment and changes caused by neutron irradiation effects.A detailed structural and thermal analysis of the DCLL TBM under typical loading conditions was performed. Highly stressed locations in the TBM were identified and the stress was broken down into membrane, bending, secondary, and peak stress for evaluating local stress intensities and equivalent stress in order to apply the SDC-IC design rules. Both low- and high temperature damage rules were evaluated to show lack of excessive deformation and negligible thermal creep.

Cyclic stress–strain response of compacted gravel

The positive effect of artificial densification on the stress–strain performance of granular materials is acknowledged from very ancient times but its importance greatly increased after the development of powerful machineries for the construction of large earth and rockfill dams. It is, however, pointed out that the extensive exploitation of gravelly soil is rarely supported by a thorough analytical assessment of the compaction effects on the constitutive relationships of materials, as would be desirable considering the massive dimension of these works and the complexity of typical loading conditions. The present research aims to fill this gap by means of a detailed experimental investigation and a theoretical analysis on the stress–strain response of dense gravels under monotonic and cyclic loading. The experimental campaign consists of a large number of triaxial tests performed at different initial mean effective stresses, following different stress paths and sequences, on artificially reconstituted samples of large dimensions compacted at different initial densities. The great care placed in the accuracy of laboratory instrumentation enables a high repeatability of experimental results, which is necessary to provide a clear focus on non-linearity in the limited strain range of the pre-failure response of the gravel. Based on the curve-fitting method the ingredients of an elasto-plastic constitutive model have been defined to predict the response of gravel under monotonic and cyclic loading. Elastic stiffness is simulated with a model derived from the literature which assumes a dependency on soil density together with inherent and stress-induced anisotropy. Plastic strain development from different initial stress and volume states of gravel is simulated by a critical state, multiple yielding constitutive model. Hardening and flow rules for the latter have been obtained by modifying previously existing laws in order better to reproduce the observations under monotonic compression, extension and cyclic loading. Validation of the proposed model is finally provided by comparing simulations and experimental results in a variety of testing conditions.

Investigation on Buckling of Cylindrical Shells and Influences of Boundary Conditions

Thin-walled cylindrical shells are widely used in many industrial sectors as light structural elements. Determination of their buckling strength under various types of loading conditions is a crucial work for engineering design. Due to the needs of research of crashworthiness, dynamic buckling of cylindrical shells subjected to the strong axial impact becomes a frontier issue in recent years. The axial impact is a very complex dynamic process because of the coupling of multiple effects. In this paper, the buckling mechanism of cylindrical shells subjected to axial impact and the influences of boundary conditions, and energy absorption properties have been investigated by experiments.

Correlation between crystallographic orientation and mechanical response in a three-dimensional β-Ti microstructure

Abstract

Field Layout of Glass Reinforced Epoxy Pipeline – A Practical Approach

This paper presents a practical approach dealing with the development of safe working envelops for field operators to avoid any potential GRE pipe failure during installation. Finite element modeling was used to model the pipeline. Two different element types available in ANSYS library (Beam and Shell elements) were used in the analysis. Various pipe sizes subjected to typical loading conditions similar to field layout conditions were considered. The finite element models were used to estimate pipe deflection, the internal normal and shear forces as well as bending moments for each pipe section along its length from which the induced stresses were determined. The maximum tensile stress was calculated and compared to the failure strength of GRE for various lifting scenarios. A sensitivity analysis on the various parameters affecting the structural integrity of the pipeline was also performed. It was found that the beam element over predicts the threshold lifting height as compared to the shell element results. In most cases, the estimated threshold value for the lifting height causing potential pipe failure for all pipe sizes is 2 and 1.2 m for beam and shell elements, respectively. Moreover, the results showed that the minimum threshold height increases for smaller pipe sizes.

Time and temperature effects on Poisson’s ratio of poly(butylene terephthalate)

The viscoelastic nature of the Poisson's ratio of a semicrystalline poly (butylene terephthalate) is highlighted by investigating its dependence on time, temperature and strain rate, under two types of loading conditions: i) constant defor- mation rate tests, in which the transverse strain is measured in tensile ramps at various temperatures and at two strain rates; and ii) constant deformation tests, in which, under a constant axial deformation, the transverse strain is measured as a func- tion of time in isothermal experiments performed at various temperatures. In both testing configurations, axial and trans- verse deformations are measured by means of a biaxial contact extensometer, and a correction procedure is adopted in order to compensate the lateral penetration of the extensometer knives. Poisson's ratio displays the typical features of a retarda- tion function, increasing with time and temperature, and decreasing with strain rate. This behaviour has been compared to that of simultaneously measured relaxation modulus.

An Efficient Neural Network Based Modeling Method for Automotive EMC Simulation

This paper presents a newly developed methodology for VHDL-AMS model integration into SPICE-based EMC simulations. To this end the VHDL-AMS model, which is available in a compiled version only, is characterized under typical loading conditions, and afterwards a neural network based technique is applied to convert characteristic voltage and current data into an equivalent circuit in SPICE syntax. After the explanation of the whole method and the presentation of a newly developed switched state space dynamic neural network model, the entire analysis process is demonstrated using a typical application from automotive industry.

Corrosion fatigue crack propagation in a heat affected zone of high-performance steel in an underwater sea environment

Fatigue crack propagation in high-performance steel, HSB800, was investigated in air and seawater environments using three-point single-edge notched bending fatigue tests. Two types of heat affected zones (HAZ) resulting from welding processes, coarse grained and inter-critically reheated coarse grained zones, together with as-received metal were used to analyze the behavior. A 3.5% sodium chloride solution was used as the seawater, and several types of loading conditions, according to the stress ratio and loading frequency, were applied. The fatigue crack propagations were then assessed using the da/dN–Δ K curves. The results showed that the corrosion fatigue crack in seawater was more rapidly propagated than was that in the air environment. The third region of crack propagation was not observed in the da/dN–Δ K curve for the seawater environment, particularly in base metal. Generally, high stress ratio and load frequency shows a low threshold value in the stress intensity factor range. Furthermore, a different microstructural aspect of the crack propagation behavior in HAZs, as compared with that of the base metal, has been identified according to the crack propagation mechanisms.