Quasi-static Test Data Research Articles

Seismic behavior and failure analysis of prefabricated foamed concrete composite walls for passive houses

In view of the lack of research on the failure mode and seismic behavior of high-performance insulation walls utilizing lightweight concrete as the structural material, this study presents experimental findings from a seismic behavior investigation of prefabricate foamed concrete composite walls (PFCCWs) for passive house in China. The PFCCWs incorporate low thermal conductivity and high-strength foamed concrete, polyurethane, decorative magnesium straw slabs to provide excellent thermal and mechanical properties for prefabricated passive houses in hot summer and cold winter area. The seismic behavior of PFCCWs under different influence factors were elaborated using quasi-static test data and observation of external damage. The lightweight and porous nature of foamed concrete leads to significant crack formation during failure. The findings suggest that the skin effect of magnesium straw slabs and polyurethane impedes crack development and improve the load-bearing capacity with ductility enhancement. Additionally, reducing the aspect ratio and substituting post-cast column concrete with common concrete are effective to improve the seismic behavior. The window opening changes the worst damage area of the wall and notably weakens the seismic behavior. The enhanced integrity of cast-in-place wall leads to the difference in the failure mechanism and increases in load-bearing and deformation capacities. Meanwhile, design suggestions for the foamed concrete insulation walls are also proposed by comparing the failure mode and hysteretic response of various wall types.

A physics-informed impact model refined by multi-fidelity transfer learning

Impact performance is a key consideration when designing objects to be encountered in everyday life. Unfortunately, how a structure absorbs energy during an impact event is difficult to predict using traditional methods, such as finite element analysis, because of the complex interactions during high strain-rate compression. Here, we employ a physics-based model to predict impact performance of structures using a single quasistatic experiment and refine that model using intermediate strain rate and impact testing to account for strain-rate dependent strengthening. This model is trained and evaluated using experiments on additively manufactured generalized cylindrical shells. Using transfer learning, the trained model can predict the performance of a new design using data from a single quasistatic test. To validate the transfer learning model, we extrapolate to new impactor masses, new designs, and a new material. The accuracy of this model allows researchers to quickly screen new designs or leverage pre-existing databases of quasistatic test data. Furthermore, when impact tests are necessary to validate design selection, fewer impact tests are necessary to identify optimal performance.

Out-of-plane behaviors of unreinforced and spray polyurea retrofitted one-way masonry infilled walls

Unreinforced masonry infilled wall (MIW) is prone to out-of-plane (OOP) crack, bend, and collapse when subjected to OOP quasi-static and blast loadings. Spray polyurea (SPUA) is an excellent retrofitted material for MIW to improve its blast resistance and reduce fragmentation. Aiming to study the OOP behaviors of one-way unreinforced and SPUA retrofitted MIW under quasi-static and blast loadings, the corresponding OOP resistance functions of MIW under uniform loading are firstly established. The critical collapse deflection of unreinforced MIW is determined as δ = t-a, and the ultimate deflection of SPUA retrofitted MIW depends on the fracture strain of SPUA. Then, the quasi-static OOP uniform loading test on two full-scale one-way MIW was performed, and the OOP loading-deflection curves of MIW were obtained. It indicated that MIW is divided into two parts by the mid-height horizontal crack, and the upper and lower parts are rotated around the top and bottom mortar joints. Furthermore, by comparing with the present and existing quasi-static test data on unreinforced and SPUA retrofitted MIW, as well as the specified resistance functions by regulations (UFC 3-340-02, Eurocode 6, FEMA 306/356) and previous scholars, the applicability of established OOP resistance functions is validated. Finally, the equivalent single degree of freedom (SDOF) calculation approach to predict the dynamic responses of one-way unreinforced and SPUA retrofitted MIW under blast loadings is proposed based on the established resistance functions. The comparisons with five series blast tests demonstrate that the proposed SDOF approach can well predict the OOP deflection of MIW and evaluate whether the wall collapses or not. This work can provide a helpful reference for the blast-resistant evaluation and design of unreinforced and SPUA retrofitted MIW.

Parameter identification of hysteresis model of reinforced concrete columns considering shear action

It is necessary to determine the load-displacement hysteresis relationship of the reinforced concrete (RC) columns to accurately predict the nonlinear dynamic response of RC columns during earthquakes. In this paper, 17 rectangular RC columns were tested under horizontal cyclic loading and the hysteresis characteristics of RC columns considering shear action were obtained. Then, the influences of Bouc-Wen-Baber-Noori (BWBN) restoring force model parameters on the hysteresis loops of RC columns were analyzed. Based on the quasi-static test data of rectangular RC columns failed in flexural-shear and shear collected from the PEER-Structural Performance Database and the tests in this paper, a parameter identification method for the BWBN model of RC columns was proposed. After that, the probability distribution and the statistical value of the major influencing parameters of BWBN model for shear-dominated RC columns were calculated. The results show that the BWBN model can accurately predict the hysteresis loops of RC columns under cyclic loading and describe the hysteresis characteristics of shear-dominated RC columns, such as strength, stiffness degradation, and pinch effect. The proposed method can identify BWBN model parameters for shear-dominated RC columns well, and the main distribution range of strength degradation parameter δv, stiffness degradation parameter δη, and pinch effect parameter ζs increase gradually with the failure mode of RC columns from flexural-shear failure to shear failure, indicating that the degradation and pinch effect of RC columns failed in shear is more significant than that of flexural-shear. The presented approach is also appropriate for other components or structures, which lays a foundation for further seismic dynamic response analysis.

Numerically efficient analysis of concrete-filled steel tubular columns under lateral impact loading

Concrete-filled steel tube (CFST) columns have been gradually used as an alternative to conventional reinforced concrete columns because of their excellent vertical and lateral bearing capacity, particularly when columns have a high risk of impact loading. Three-dimensional detailed finite element (FE) models are usually employed to estimate the impact-resistant performance of CFST columns under impact loadings. However, detailed FE models are typically complex in modeling and low in calculation efficiency as well as require high performance in computer hardware. Hence, this paper aims to develop an alternative modeling method that can predict the impact behavior of CFST columns with high efficiency and low requirements in computer resources. The developed method includes a contact model using mass-spring-damper elements to describe the contact behavior between the impactor and the impacted CFST columns and a nonlinear fiber-based beam-column element model to simulate the behavior of CFST columns under impact loading. The accuracies of fiber-section beam-column elements are carefully examined for CFST columns based on quasi-static test data reported in the literature. It is found that the fiber-based elements considering confinement effects induced by steel tubes can accurately predict the force versus deformation relationship of the CFST columns under monotonic loading. By incorporating the strain-rate effects of concrete and steel materials, the validated fiber-section elements are employed to simulate thirty-seven impact tests on CFST columns. Good agreements are observed between the results obtained from the developed models and the experimental data. The computational efficiency can be significantly improved by using the developed model.

Determination of material constants for high strain rate constitutive model of high entropy alloys

The paper deals with constitutive models determination for a group of high entropy materials (coded Bl-x). The procedure includes the following steps: experimental determination of mechanical characteristics for quasi-static domain through compression tests, correction of experimental data of quasi-static tests using numerical simulation, acquisition of experimental data obtained on the Split Hopkinson Pressure Bars and their simulated interpretation. Using the processed data, the constitutive patterns of the materials under investigation are drawn. The experimental data correction for quasi-static tests performed using numerical simulation involves drawing the engineering stress/strain diagram, the transition to the plastic characteristic diagram in the hypothesis of perfectly cylindrical shape of the specimen throughout the test, simulation of the compression deformation process in the presence of friction force on the end specimen surfaces and the correction of the characteristic plastic diagram using the calculated error. Dynamic data obtained on Split Hopkinson Pressure Bar were interpreted using a methodology previously published. Experimental data under real conditions are compared with data obtained by numerical simulation on an elasto-plastic model. The viscous component of the dynamic response is the difference between the real and simulated on the elasto-plastic model responses.

A coupled constitutive relation with impulse‐momentum for compressive impact behavior of the expanded polypropylene foam

In this article, the Jeong et al.'s constitutive relation and the impulse‐momentum theorem were coupled to characterize the compressive impact loading of EPP (Expanded polypropylene [EPP]) foams under varying strain rate conditions for each step. Simultaneous nonlinear Newton–Raphson method was applied to find the proper values for parameters in the constitutive relation along with quasistatic test data. Also, parameters which have physical meanings were expressed as functions of relative density. Moreover, coupling of the constitutive relation and the impulse‐momentum theorem provided transient velocities of the striker successfully. Dynamic stress‐strain curves from the analysis showed good agreement with data from instrumented impact tests and the potential to be applied to different material type polymeric foams. POLYM. ENG. SCI., 59:49–57, 2019. © 2018 Society of Plastics Engineers

Application of 2D finite element model for nonlinear dynamic analysis of clamp band joint

Due to frictional slippage between the joint components, clamp band joints may generate nonlinear stiffness and friction damping, which will affect the dynamics of the joint structures. Accurate modeling of the frictional behavior in clamp band joints is crucial for reliable estimation of the joint structure dynamics. While the finite element (FE) method is a powerful tool to analyze structures assembled with joints, it is computationally expensive and inefficient to perform transient analyses with three-dimensional (3D) FE models involving contact nonlinearity. In this paper, a two-dimensional (2D) FE model of much more efficiency is applied to investigate the dynamics of a clamp band jointed structure subjected to longitudinal base excitations. Prior to dynamic analyses, the sources of the model inaccuracy are determined, upon which a two-step model updating technique is proposed to improve the accuracy of the 2D model in accordance with the quasi-static test data. Then, based on the updated 2D model, the nonlinear influence of the clamp band joint on the dynamic response of the joint structure is investigated. Sine-sweep tests are carried out to validate the updated 2D FE model. The FE modeling and updating techniques proposed here can be applied to other types of structures of cyclic symmetry to develop accurate model with high computational efficiency.

Combined effects of high temperature and high strain rate on normal weight concrete

Concrete in structures is possibly exposed to fire and blast due to occasional accidents or terrorist attack during the service life. Yet, there are few experimental studies on the responses of normal concrete structures subjected to high temperature and high strain rate loading simultaneously, although some high strain rate experiments were performed before or after fire exposure. This paper reports an experimental study of the combined effects of high temperature and high strain rate on normal concrete material, which is a preliminary basis for calculating and assessing the performances of RC structures in blast and fire. The dynamic properties of normal concrete at elevated temperature from 20 °C up to 950 °C were systematically studied using a specially manufactured microwave–heating automatic time-controlled Split Hopkinson Pressure Bar (MATSHPB) apparatus. The concrete specimens were first efficiently heated in a specially designed industrial microwave oven, and then rapidly loaded after quickly rolling to the SHPB system. Quasi–static and low strain rate tests at elevated temperatures were also carried out for comparative analysis. In contrast with previous experimental research, the test results showed that the dynamic strength and stress–strain curve of normal concrete at high temperature still experienced remarkable strain rate effects. Moreover, the failure appearances of normal concrete subjected to both high temperature and high strain rate loading were significantly different from those of concrete at ambient temperature. In contrast with quasi-static test data, a new empirical model on dynamic increase factor of strength and secant elastic modulus of concrete at elevated temperature (DIFTS, DIFTE) were established that can be used in a very wide range of application.

Fatigue tensile behavior of carbon/epoxy composite reinforced with non-crimp 3D orthogonal woven fabric

An experimental study of the in-plane tension–tension fatigue behavior of the carbon fiber/epoxy matrix composite reinforced with non-crimp 3D orthogonal woven fabric is presented. The results include pre-fatigue quasi-static test data, fatigue life diagrams, fatigue damage progression, and post-fatigue quasi-static test data for the warp- and fill-directional loading cases. It is revealed that the maximum cycle stress corresponding to at least 3 million cycles of fatigue life without failure, is in the range of 412–450 MPa for both loading directions. This stress range is well above the static damage initiation threshold and significantly above the first static damage threshold (determined by the onset of low energy acoustic emission). The second static damage threshold, determined by the onset of high energy acoustic emission and related to the appearance of local debonds and intensive transverse matrix cracking falls within this range. The established correlation between a 3000,000 cycle fatigue stress limit on one side and the second static damage threshold stress on the other is of a high practical importance, because it will significantly reduce the amount of future fatigue tests required for this class of composites. Surprisingly, for equal maximum cycle stress level, the fatigue life under fill-directional loading appears about three times shorter than that under warp-directional loading. The 100,000 cycle, 500,000 cycle and 1000,000 cycle fatigue loading with 450 MPa maximum cycle stress has resulted in so high variations of post-fatigue static modulus, strength and ultimate strain, that no consistent and statistically meaningful trends could have been established; further extensive experimental studies are required to reliably quantify this effect.

A hyper-viscoelastic constitutive model for polyurea

This letter presents a new constitutive model for polyurea by superposing the hyperelastic and viscoelastic behaviors of polyurea. The Ogden model is used for the hyperelastic part and its parameters are determined from curve fitting of quasi-static test data. A nonlinear viscoelastic model is employed for describing the viscoelastic behavior and its relaxation time is obtained based on the test data of shear relaxation modulus. A special form of Zapas kernel for the damping function is found to be very effective to capture the viscoelastic behavior of polyurea subjected to wide ranges of strain rate. Both the versatility and accuracy of the model are examined via virtual testing.

Impact of a non-homogeneous sphere on a rigid surface

This paper examines the impact behaviour of a non-homogenous sphere (in this case a cricket ball with a rolled core construction) with a rigid surface. Experiments were carried out to measure the force-deflection behaviour of a cricket ball during a normal impact in two orientations (impacting on the seam and perpendicular to the seam). For the two orientations of impact, a disparity was found in terms of the force-deflection behaviour. Greater deformation was found for impacts landing on the seam, compared to those landing perpendicular to the seam. Comparisons with quasi-static test data suggested that only the bottom third of the ball may have been compressed during impact. The dynamic force-deflection behaviour was modelled using a mass attached to a Hertzian spring in parallel with a damper whose damping coefficient varied with the contact area. The coefficients in the model could be described using the velocity before impact alone. The model was found to be in good agreement with the experimental data. The model was then extended to predict oblique impacts by incorporating a measured coefficient of friction. This performed well in predicting the rebound velocity, angle and spin of a cricket ball after oblique impact with a cricket pitch. Inconsistencies in the results were attributed to deformation in the pitch surface.

Failure Mechanisms and the Macro-Response of Carbon Fiber Reinforced SiC Matrix Composites

Inelastic response of ceramic matrix woven 2.5 -D C/SiC composites have been analyzed using quasi-static test data. The changes in composite stiffness properties (elastic modulus, in-plane and out- ...

Influence of Microstructure on Mechanical Properties of Snow

Snow, being composed of ice grains of varying shapes, sizes, orientations, etc., has been treated as a particulate material. The mechanical properties of snow have been described in terms of microstructural parameters. A set of variables, which characterise the microstructure of snow at the granular level, has been chosen and quantified following the techniques of quantitative stereology for section plane. The data of quasi-static tests, e.g. constant strain-rate creep tests, have been analysed to determine the Young's modulus and compactive viscosity and the same have been correlated with the microstructural parameters. Inspite of scatter, definite trends are discernible. Considering the fact that deformation of snow is associated with translation and rotation of constituent grains in such a way as to attain the most stable configuration, the concept of fabric reconstruction, which is characterised by the concentration of normals (to the tangent plane at the point of grain contact) in the direction of the applied load, has been examined. The results demonstrated the occurrence of fabric reconstruction during the process of deformation. Finally, a dimensionless quantity, called the microstructural index (I), has been proposed to adequately represent the influence of microstructure.

Determination of the characteristics of viscoelastic media from the data of quasi-static tests

By representing memory-influence functions in the form of generators of the Dirac δ-function in order to describe the relaxation processes on a small initial interval [3], formulas are constructed for determining the true characteristics of viscoelastic media from the data of quasi-static creep tests and relaxation tests by means of the irreversibility effect [2], i.e., the dependence of the relaxation processes on the initial loading conditions.