Effect Of Material Variables Research Articles

Parameter identification procedure for hysteretic shear-resistant properties of beech wood dowels

To evaluate the shear-resistant behavior of wooden dowels used in Blockhaus shear walls under cyclic load, 19 specimens under ten groups of conditions were prepared and tested. The failure modes, hysteresis curves, mechanical properties, stiffness degradations, and energy dissipation capacities of the specimens were studied. The test results showed that with the increase in the number of dowels, the initial stiffness and peak load of the specimens increased greatly. The diameter of the dowels had little influence on the mechanical properties of the specimens. Furthermore, the test findings demonstrated that the pretension load between the walls greatly enhanced the initial stiffness and energy dissipation capacity of specimens. A simplified finite element model was established in Opensees. Considering the effect of material variability, the parameters of single dowel shear spring and friction spring were identified by Genetic Algorithm with modified objective function in Matlab. The identified parameters were applied to the finite element model of the multi-dowel specimens. The simulation results were in good agreement with the test results, and the validity of the numerical model and parameter identification method was verified.

Variability in the Nonlinear Modelling Parameters of Steel I‐shaped Beams Subjected to Cyclic Loading Considering Manufacturing Tolerances

AbstractThis paper focuses on the probabilistic characterization of the cyclic behaviour of steel deep members with European I‐shaped profiles. The variability of the behaviour of the member depends on several factor such as the material variability and geometrical imperfections. The effect of material variability is well recognized by the scientific community and has been considered in international design codes such Eurocode 8. European hot rolled profiles may be produced with some tolerable deviation from the nominal section in terms of shape and dimensions, which are limited by the European standard EN10034. The effect of geometrical imperfections received considerable research attention in the past. However, to the best knowledge of the authors, there are no studies that investigated the effect of the manufacturing tolerances on the behaviour of I‐shaped steel members. The tolerance range on the dimensions of the profile can be significant. The change in the dimensions of the profile changes the web and flange slenderness which may have a significant influence on the flexural behaviour. Thus, the characterisation of the effect of the manufacturing tolerances on the behaviour of the members is of paramount interest. For this purpose, an advanced finite element model, validated with past experimental data, was developed and an extensive parametric study is conducted. Then, statistical methods are used to characterise the variability using different distributions

Effect of material variability on the seismic response of reinforced concrete box-girder bridges for different pier heights

RC bridges situated in regions prone to seismic activity are susceptible to undesirable pier column movements and deck displacements. The component-level nonlinear response evaluation can give a better picture of the seismic safety of the existing bridge structures. Many times, the material strength variability also affects the inelastic response of the structures significantly. The present study looks into the effects of column heights and material strength variability on the seismic performance of reinforced concrete bridge models adopted from past investigations, subjected to bi-directional loading. Chosen suite of 40 far-field ground excitations are employed to simulate the seismic response of chosen models in OpenSees and their non-linear response is evaluated. The seismic response of the structure is evaluated as curvature ductility of piers (primary component), and deck displacements (secondary component). Fragility curves so obtained across the damage states considered depict the difference in seismic performance of the model considering only record variability and considering record and material strength uncertainties. The results showed that for the primary component, damage probability for different states is found to be increased under material variability irrespective of the column pier height, while secondary components showed an increase in the damage state due to material strength variability for the shorter pier.

Triboinformatics Approach for Friction and Wear Prediction of Al-Graphite Composites Using Machine Learning Methods

Abstract Data-driven analysis and machine learning (ML) algorithms can offer novel insights into tribological phenomena by establishing correlations between material and tribological properties. We developed ML algorithms using tribological data available in the literature for predicting the coefficient of friction (COF) and wear-rate of self-lubricating aluminum graphite (Al/Gr) composites. We collected data on effects of material variables (graphite content, hardness, ductility, yield strength, silicon carbide content, and tensile strength), processing procedure, heat treatment and tribological test variables (normal load, sliding speed, and sliding distance) on tribological properties and established two-parameter relationships. These data are analyzed using several ML algorithms: artificial neural network (ANN), K nearest neighbor (KNN), support vector machine (SVM), gradient boosting machine (GBM), and random forest (RF). The trained ML models can predict the tribological behavior from material variables and test conditions, beyond what is possible from two-parameter correlations. GBM outperformed other ML algorithms in predicting friction behavior, while RF had the best prediction of the wear behavior. ML analysis identified graphite content and hardness and as the most significant variables in predicting the COF, while graphite content and sliding speed were the most dominant variables for wear-rates.

Simulating the induction heating of cross-ply C/PEKK laminates – sensitivity and effect of material variability

A simulation model for the induction heating of UD tape-based thermoplastic composites is presented in this work. The model is based on the electrical ply properties which were determined experimentally for two commercially available carbon reinforced tape materials. Moreover, the interrelation between the measured electrical conductivities and the fiber distribution in the tape and laminates is discussed based on microscopic structure evaluation. The model was validated experimentally for the induction heating of cross-ply laminates. Subsequently, the effect of the experimental variability in the measured conductivities on the heating behavior was investigated using the simulation model. It was found that the material variability can have a significant effect on the heating behavior.

Stochastic time domain spectral element analysis of beam structures

In this work, a stochastic time domain spectral element method (STSEM) is proposed for stochastic modeling and uncertainty quantification of engineering structures. To perform the analysis, both an isotropic Timoshenko beam (TB) and a sandwich beam are considered. The sandwich beam is modeled considering higher-order sandwich panel theory which is capable of addressing the core flexibility. The material properties are considered as 1D non-Gaussian random fields, and optimal linear estimation (OLE) is used for the discretization of the random fields. The OLE-based discretization of a random field allows simulating the random fields numerically, resulting in realizations of the stiffness, mass matrix, and dynamic stiffness matrix. In the current work, the computationally efficient time domain spectral element method (TSEM) is used to develop the STSEM formulation. The STSEM reduces the CPU time significantly as the number of degrees of freedom (dof) is much smaller than in FEM. TSEM also provides a consistent diagonal mass matrix which reduces the computation cost in case of dynamic problems. The deflection statistics of the beam for static, free vibration and dynamic cases are investigated for both TB and sandwich beam. The computational efficiency of the proposed method and the effect of material variability on the response statistics are also discussed. Moreover, the effect of different correlation lengths on the response statistics is studied.

Effect of Material Variability and Mechanical Eccentricity on the Seismic Vulnerability Assessment of Reinforced Concrete Buildings

The present paper deals with the influence of material variability on the seismic vulnerability assessment of reinforced concrete buildings. Existing r.c. buildings are affected by a strong dispersion of material strengths of both the base materials. This influences the seismic response in linear and nonlinear static analysis. For this reason, it is useful to define a geometrical parameter called “material eccentricity”. As a reference model, an analysis of a two storey building is presented with a symmetrical plan but asymmetrical material distribution. Furthermore, an analysis of two real buildings with a similar issue is performed. Experimental data generate random material distributions to carry out a probabilistic analysis. By rotating the vector that defines the position of the center of strength it is possible to describe a strength domain that is characterized by equipotential lines in terms of the Risk Index. Material eccentricity is related to the Ultimate Shear of non-linear static analyses. This relevant uncertainty, referred to as the variation of the center of strength, is not considered in the current European and Italian Standards. The “material eccentricity” therefore reveals itself to be a relevant parameter to considering how material variability affects such a variation.

Effect of material variability and compacted layers on transfer processes in heterogeneous waste rock piles

The heterogeneity of waste rock piles is due to the wide and variable grain size distribution of waste rock and construction methods leading to complex internal structures. The general objective of this work was to better understand the effect of such heterogeneity on the coupled transfer processes acting within waste rock piles producing Acid Mine Drainage (AMD). For this purpose, parametric numerical simulations were conducted with the TOUGH AMD numerical simulator, considering 1) three random spatial distributions of the same material properties to assess the resulting behavior, 2) four ranges of material properties with the same spatial distribution to evaluate the effect of the degree of heterogeneity, and 3) the effect of compacted layers due to circulation of heavy equipment during construction. Results show that fine-grained (denser with lower permeability) material present near the boundary of a pile can limit air entry. Coarse materials promote preferential flow of gas and water vapor. Fine-grained materials beneath the pile surface favor the internal condensation of water vapor and thus minimize water loss. The initiation of secondary gas convection cells requires a minimal degree of heterogeneity, which is closely related to the range of permeability between the coarse and the finer material ratio (k(coarse)/k(fine)). The presence of coarse grained material in the pile does not necessarily lead to more convection and higher AMD production. The magnitude of convection rather depends on the amount of fine-grained material and its distribution in the pile. Results also show that low-permeability compacted layers strongly limit convection. Results thus support waste rock pile construction methods integrating fine-grained materials or compacted layers to minimize AMD production.

PERFORMANCE OF PRESSURE TUBES IN CANDU REACTORS

The pressure tubes in CANDU reactors typically operate for times up to about 30 years prior to refurbishment. The in-reactor performance of Zr-2.5Nb pressure tubes has been evaluated by sampling and periodic inspection. This paper describes the behavior and discusses the factors controlling the behaviour of these components. The Zr–2.5Nb pressure tubes are nominally extruded at 815 °C, cold worked nominally 27%, and stress relieved at 400 °C for 24 hours, resulting in a structure consisting of elongated grains of hexagonal close-packed alpha-Zr, partially surrounded by a thin network of filaments of body-centred-cubic beta-Zr. These beta-Zr filaments are meta-stable and contain about 20% Nb after extrusion. The stress-relief treatment results in partial decomposition of the beta-Zr filaments with the formation of hexagonal close-packed alpha-phase particles that are low in Nb, surrounded by a Nb-enriched beta-Zr matrix. The material properties of pressure tubes are determined by variations in alpha-phase texture, alpha-phase grain structure, network dislocation density, beta-phase decomposition, and impurity concentration that are a function of manufacturing variables. The pressure tubes operate at temperatures between 250 °C and 310 °C with coolant pressures up to about 11 MPa in fast neutron fluxes up to 4 × 1017 n·m−2·s−1 (E > 1 MeV) and the properties are modified by these conditions. The properties of the pressure tubes in an operating reactor are therefore a function of both manufacturing and operating condition variables. The ultimate tensile strength, fracture toughness, and delayed hydride-cracking properties (velocity (V) and threshold stress intensity factor (KIH)) change with irradiation, but all reach a nearly limiting value at a fluence of less than 1025 n·m−2 (E > 1 MeV). At this point the ultimate tensile strength is raised about 200 MPa, toughness is reduced by about 50%, V increases by about a factor of 6, while KIH is only slightly reduced. The role of microstructure and trace elements in these behaviours is described. Pressure tubes exhibit elongation, diametral expansion, and sag. The deformation behaviour is a function of operating conditions and the material properties that vary from tube-to-tube and as a function of axial location. Semi-empirical predictive models have been developed to describe the deformation response of average tubes as a function of operating conditions. The effect of material variability on corrosion behaviour is less well defined compared with other properties but there are instances where tube orientation and ingot source can be identified as factors that have an effect on hydrogen pick-up.

Effect of Material Variability on Multiscale Modeling of Rate-Dependent Composite Materials

AbstractThe effects of material variability on the mechanical response and failure of composites under high strain rate and impact loading are investigated in this paper. A previously developed strain rate–dependent, sectional micromechanics model is extended to account for the variability in microstructure and constituent material properties. The model presented in this paper also includes a three-dimensional damage law based on a work potential theory and a microscale failure criterion. Microstructural characterization of the composite is performed to obtain the statistical distributions needed for the stochastic methodologies. A Latin hypercube sampling technique is used to model the uncertainties in fiber volume fraction and viscoplastic material constants. A comparison of general Monte Carlo simulation and Latin hypercube–based Monte Carlo shows that the Latin hypercube technique converges using fewer simulations. The modulus and failure strain obtained using the developed methodology show good corre...

Drift-based and dual-parameter fragility curves for concentrically braced frames in seismic regions

This paper discusses the development of drift-based and dual-parameter fragility curves for steel braces as part of concentrically braced frames designed in seismic regions. The experimental results from 24 different research programs are compiled into a database for this effort. Drift-based fragility curves are developed for three damage states of steel braces subjected to cyclic loading associated with brace flexural buckling, local buckling and brace strength loss due to fracture. The effects of material variability, brace cross sectional shape and loading protocol on the drift-based fragility curves are investigated. The effect of global and local slenderness ratios on the fracture ductility of various shapes of steel braces is examined through dual-parameter fragility curves that relate these geometric ratios with the expected story drift ratios that each of the three pre-described damage states occur. The proposed fragility curves can be employed for rapid assessment of the seismic vulnerability of concentrically braced frames.

Effects of material variability on the ductility of composite beams and overstrength coefficients

SUMMARYThe aim of this paper is to investigate the plastic rotation capacity of composite beams as well as the overstrength factors for composite joints considering the actual European steel production. It relies on the statistical data of the mechanical properties of steel profiles and reinforcement bars produced in several European steel mills that have been collected during the European research project OPUS. Several steel and composite structures have been designed following the EN 1998 rules, and the effect of the statistical distribution of the steel properties on the design has been analyzed. In such structures, the first attainment of the rotation capacity is expected to happen in the hogging region. The plastic rotation capacity was evaluated using the so‐called standard beam concept. The moment–rotation curve was constructed by joining together the pre‐buckling branch, determined using a fiber model, and the post‐buckling part derived by considering the local plastic failure mechanism as suggested by Gioncu. A program in MATLAB (MATLAB version 7.10.0. Natick, Massachusetts: The MathWorks Inc., 2010) was developed to establish such curve for arbitrary composite beams. The predictions of the model compare favorably against the experimental results. On the basis of the probabilistic model for the mechanical properties of steel, we derive the statistical distribution of the maximum rotation defined at the intersection of the pre‐buckling and post‐buckling curves. Next, we estimate the so‐called overstrength factors. Copyright © 2012 John Wiley & Sons, Ltd.

In-reactor performance of pressure tubes in CANDU reactors

The pressure tubes in CANDU reactors have been operating for times up to about 25 years. The in-reactor performance of Zr–2.5Nb pressure tubes has been evaluated by sampling and periodic inspection. This paper describes the behaviour and discusses the factors controlling the behaviour of these components in currently operating CANDU reactors. The mechanical properties (such as ultimate tensile strength, UTS, and fracture toughness), and delayed-hydride-cracking properties (crack growth rate V c, and threshold stress intensity factor, K IH) change with irradiation; the former reach a limiting value at a fluence of <1 × 10 25 n m −2, while V c and K IH reach a steady-state condition after a fluence of about 3 × 10 25 n m −2 and 3 × 10 24 n m −2, respectively. At saturation the UTS is raised by about 200 MPa, toughness is reduced to about 40% of its initial value, V c increases by about a factor of ten while K IH is only slightly reduced. The role of microstructure and trace elements in these behaviours is described. Pressure tubes exhibit elongation and diametral expansion. The deformation behaviour is a function of operating conditions and material properties that vary from tube-to-tube and as a function of axial location. Semi-empirical predictive models have been developed to describe the deformation response of average tubes as a function of operating conditions. For corrosion and, more importantly deuterium pickup, semi-empirical predictive models have also been developed to represent the behaviour of an average tube. The effect of material variability on corrosion behaviour is less well defined compared with other properties. Improvements in manufacturing have increased fracture resistance by minimising trace elements, especially H and Cl, and reduced variability by tightening controls on forming parameters, especially hot-working temperatures.

The effect of material and ground motion uncertainty on the seismic vulnerability curves of RC structure

Starting from the premise that vulnerability curves are an indispensable ingredient of earthquake loss assessment, this paper focuses on establishing the relative effect of strong-motion variability and random structural parameters on the ensuing vulnerability curves. Moreover, the effect of the selection of statistical models used to present simulation results is studied. A three story ordinary moment resisting reinforced concrete frame, previously shake-table tested, is used as a basis for the fragility analysis. The analytical environment and the structural model are verified through comparison with shaking-table test results. The selection of ground motion sets, definition of limit states, statistical manipulation of simulation results, and the effect of material variability are investigated. No approximations are used to reduce the sample size or minimize the analytical effort, in order that attention is focused on the parameters under investigation. Notwithstanding the limited scope of the study, the results presented indicate that the effect of randomness in material response parameters is far less significant than the effect of strong-motion characteristics. Therefore, the importance of scrupulous selection and scaling of strong-motion and use of appropriate limit states and statistical models is emphasized.

Development of a mathematical model for the pultrusion of unsaturated polyester resin

AbstractA mathematical model is developed for simulating the pultrusion process of unsaturated polyester resin, using a mechanistic kinetic model based on free radical polymerization. In their previous publications (Refs. 1 and 7), Han and Lee used the mechanistic model to simulate the curing behavior of unsaturated polyester resins under isothermal conditions, employing the differential scanning calorimetry data obtained for a range of single initiators and multiple initiator systems. For the sake of mathematical convenience, a pultrusion die of cylindrical geometry was considered. The mathematical model developed permits one to choose any number of initiators when predicting the distributions of the degree of cure and temperature in both the radial and axial directions of the die. The effects of material variables (e.g., the type and concentration of mixed initiators) and processing conditions (e.g., pulling speed and die temperature distribution) on the performance of the pultrusion are evaluated.

Stochastic Simulation of Wood Load-Sharing Systems

A generalized procedure was developed to predict the effect of material variability on the variability of system performance when the material properties of the system component members are correlated. This procedure utilized Monte Carlo simulations to predict the load-carrying capacity (strength behavior) of parallel-member wood load-sharing systems from a linear-elastic mathematical model also developed in this study. The simulated strength behavior obtained using this procedure was compared to the strength behavior of actual wood load-sharing systems tested to failure. This simulation technique was shown to be an extremely good predictor of system variability. Although this procedure was developed for specific application to the prediction of wood-joist floor behavior, it can easily be applied to any area of structures research in which the members exhibit correlated properties.

The Effect of Material Variables on the Fatigue Life of AISI 52100 Steel Ball Bearings

The effect of material variables on the fatigue life of AISI 52100 steel in ball bearings is examined. An apparently significant negative correlation with the abundance of certain trace alloying elements has been found. An effect of gas content has not been proven. Some difference in the endurance of bearings tempered for various lengths of time at different temperatures is shown. The most effective means available for obtaining improved fatigue life are certain techniques of vacuum melting. An approximate two-fold increase over catalog fatigue life is obtained by single vacuum melting, and a 7.7-fold increase has been achieved in tests using multiple consumable electrode vacuum remelting. This, in conjunction with previously reported evidence for the existence of a lower limit for fatigue life, suggests the possibility of producing bearings with better than 99.5% reliability at catalog life.