Monotonic Quasi-static Loading Research Articles

Investigation on the influence of previous in-plane loading on the out-of-plane behavior of the innovative damped masonry infill wall

The damped masonry infill wall (DMIW) is an innovative masonry infill wall (MIW), wherein multiple horizontal subpanels, also called masonry units, are subdivided by inserting the horizontal damping layer joints (DLJs). While existing research on DMIW primarily focuses on its pure in-plane (IP) and pure out-of-plane (OOP) behavior, it is crucial to account for the interaction effect between IP and OOP behaviors to accurately assess OOP performance, Failure to consider this interaction may lead to an overestimation of OOP capacity, a concern previously highlighted in traditional MIW studies. Addressing this gap, this study conducts a sequential experiment involving IP cyclic quasi-static loading followed by OOP monotonic quasi-static loading. The aim is to examine the influence of previous IP cyclic loading on OOP behavior, considering factors such as OOP damage evolution, performance parameters, deformation patterns, and resistance mechanisms. The results show that, in DMIW, the effect of previous IP cyclic loading on the reduction of OOP performance is significantly lower compared to traditional MIW. Furthermore, the fundamental OOP resistance mechanism of DMIW remains unchanged under IP-OOP sequential loading. However, the OOP deformation pattern is altered due to the previous horizontal cracks developed in the masonry units under IP cyclic loading. Finally, a simple bi-linear equation is derived to quantify the effect of the previous IP cyclic loading on the primary OOP performance parameters of the DMIW.

Critical loss of primary implant stability in osteosynthesis locking screws under cyclic overloading

Primary implant stability, which refers to the stability of the implant during the initial healing period is a crucial factor in determining the long-term success of the implant and lays the foundation for secondary implant stability achieved through osseointegration. Factors affecting primary stability include implant design, surgical technique, and patient-specific factors like bone quality and morphology. In vivo, the cyclic nature of anatomical loading puts osteosynthesis locking screws under dynamic loads, which can lead to the formation of micro cracks and defects that slowly degrade the mechanical connection between the bone and screw, thus compromising the initial stability and secondary stability of the implant. Monotonic quasi-static loading used for testing the holding capacity of implanted screws is not well suited to capture this behavior since it cannot capture the progressive deterioration of peri‑implant bone at small displacements. In order to address this issue, this study aims to determine a critical point of loss of primary implant stability in osteosynthesis locking screws under cyclic overloading by investigating the evolution of damage, dissipated energy, and permanent deformation. A custom-made test setup was used to test implanted 2.5 mm locking screws under cyclic overloading test. For each loading cycle, maximum forces and displacement were recorded as well as initial and final cycle displacements and used to calculate damage and energy dissipation evolution. The results of this study demonstrate that for axial, shear, and mixed loading significant damage and energy dissipation can be observed at approximately 20 % of the failure force. Additionally, at this load level, permanent deformations on the screw-bone interface were found to be in the range of 50 to 150 mm which promotes osseointegration and secondary implant stability. This research can assist surgeons in making informed preoperative decisions by providing a better understanding of the critical point of loss of primary implant stability, thus improving the long-term success of the implant and overall patient satisfaction.

Strength and Deformation of Concrete-Encased Grouting-Filled Steel Tubes Columns Exposed to Monotonic Quasi-Static Loading Conditions

This study aimed to evaluate the effectiveness of a novel concrete-encased column (CE) using small circular steel tubes filled with cementitious grouting material (GFST) as the primary reinforcement instead of traditional steel bars. The research involved three different types of reinforcement: conventional steel bars, concrete-filled steel tubes with 30% of the reinforcement ratio of steel bars, and concrete-filled steel tubes with the same reinforcement ratio as steel bars. Twenty-four circular concrete columns were tested and categorized into six groups based on the type of reinforcement employed. Each group comprised four columns, with one subjected to concentric axial load, two subjected to eccentric axial load (with eccentricities of 25 mm and 50 mm, respectively), and one tested under lateral flexural loads. To validate the experimental results, finite element (FE) analysis was conducted using ABAQUS software version 6.14. The experimental findings for concentric load reveal that columns with the second type of reinforcement, concrete-filled steel tubes with 30% of the reinforcement ratio of steel bars exhibited a failure load 19% lower than those with steel bars, while columns with the third type of reinforcement, concrete-filled steel tubes with the same reinforcement ratio as steel bars achieved a failure load 17% greater than the traditional steel bars. The FE analysis demonstrates good agreement with the experimental outcomes in terms of ultimate strength, deformation, and failure modes.

A study on microcrack monitoring in concrete: discrete element method simulations of acoustic emission for non-destructive diagnostics

The research is focused on the monitoring of fracture evolution in concrete beams under three-point bending using the acoustic emission technique and the discrete element method. The main objective of the study was to numerically and experimentally investigate the mechanism behind the generation of elastic waves during acoustic emission events and their interaction with micro- and macro-cracking in concrete beams under monotonic quasi-static loading. This was achieved through the development of a DEM model and numerical modelling of AE effects. An improved 4-phase DEM model of concrete including real mesostructured specimens and the ability to simulate aggregate breakage was introduced. The propagation of elastic waves, recorded in both laboratory experiments and numerical calculations, was given particular attention. The results showed the high suitability of the developed DEM model for monitoring crack initiation, development and propagation, as well as for supporting the interpretation of diagnostic results obtained by acoustic emission techniques.

A coupled plasticity-damage cohesive-frictional interface for low-cycle fatigue analysis

A novel thermodynamically consistent cohesive-frictional model for the analysis of interface degradation and failure under either monotonic quasi-static loading or cyclic loading in low-cycle fatigue problems is proposed.Starting from the definition of a suitable Helmholtz energy density function, a phenomenological interface model is developed in the framework of plasticity and damage mechanics. In particular, a coupled plasticity-damage activation function is defined and employed together the consistent evolution rules to capture the evolution of damage and plasticity under the action of the external loads. Due to the specific features of such threshold and flow rules, the initiation and accumulation of damage under monotonic increasing loads is captured and accompanied by negligible plastic evolution, allowing to approximate pure damage-based cohesive laws. On the other hand, coupling associative plasticity and damage evolution allows linking the interface degradation in low-cycle fatigue processes to plastic hysteresis, on the basis of the phenomenological assumption that no infinite plastic flows may happen without microstructural transformation leading to loss of load bearing capability. The model also embodies a smooth transition from an initially cohesive to a residual frictional interface behaviour, governed by a Coulomb frictional activation function.The developed formulation has been implemented and assessed for individual interfaces, highlighting consistent phenomenological behaviour. It has been then applied to the analysis of delamination and de-bonding in composite test cases, showing accuracy against experimental data and confirming its potential.

Methodology for the systematic investigation of the hygrothermal-mechanical behavior of a structural epoxy adhesive

A methodology is presented for the systematic determination of moisture absorption behavior of a structural epoxy adhesive in order to investigate the influence of humidity on the strength, fracture energy and fracture strain of adhesively bonded joints subjected to monotonic quasi-static loading. The first step consists of a preliminary weighting test to assess the parameters of the Fick diffusion model for the adhesive at hand by means of a thin disc made of cured adhesive bulk material. Numerical simulations verify the applied assumption of one-dimensional diffusion. It turns out that the adhesive disc is not thin enough in order to achieve reasonable testing times up to saturation for the complete characterization of moisture absorption. Therefore, the specimen thickness is systematically reduced. In the second step, the diffusion behavior of the adhesive is characterized. In order to get a homogeneous humidity level within the whole specimen, several adhesive discs are exposed to a reference temperature and humidity, according to the prior dimensioning. This novel procedure of preconditioning allows for a homogeneous and, thus, well-defined initial state of water content in the specimens. From this state, the discs are exposed to various environmental conditions, which include different temperatures and relative humidity of the surrounding moist air. It is observed that moisture saturation primarily depends on the relative humidity, while the diffusion coefficient depends on temperature for this epoxy adhesive. Fick's model of diffusion is applied to represent the moisture uptake of the adhesive at hand, whereby the initial state of water saturation after preconditioning is taken into account. Based on the findings in step 1 and 2, the influence of moisture is determined in step 3 on the strength, fracture energy and elongation at rupture of adhesively bonded joints. Thick adherend shear specimens (TASSs) are preconditioned in order to achieve a variety of homogeneous moisture states in the corresponding adhesive layer. After preconditioning, quasi-static tensile tests of the TASSs are carried out at various temperature levels. The experimental results reveal that the strength and fracture energy of the TASS degrades progressively with higher temperature and increased humidity.

Thermal, Mechanical and Chemical Analysis of Poly(vinyl alcohol) Multifilament and Braided Yarns.

Poly(vinyl alcohol) (PVA) in multifilament and braided yarns (BY) forms presents great potential for the design of numerous applications. However, such solutions fail to accomplish their requirements if the chemical and thermomechanical behaviour is not sufficiently known. Hence, a comprehensive characterisation of PVA multifilament and three BY architectures (6, 8, and 10 yarns) was performed involving the application of several techniques to evaluate the morphological, chemical, thermal, and mechanical features of those structures. Scanning electron microscopy (SEM) was used to reveal structural and morphological information. Differential thermal analysis (DTA) pointed out the glass transition temperature of PVA at 76 °C and the corresponding crystalline melting point at 210 °C. PVA BY exhibited higher tensile strength under monotonic quasi-static loading in comparison to their multifilament forms. Creep tests demonstrated that 6BY structures present the most deformable behaviour, while 8BY structures are the least deformable. Relaxation tests showed that 8BY architecture presents a more expressive variation of tensile stress, while 10BY offered the least. Dynamic mechanical analysis (DMA) revealed storage and loss moduli curves with similar transition peaks for the tested structures, except for the 10BY. Storage modulus is always four to six times higher than the loss modulus.

Finite element modelling of composite castellated beam

Nowadays, castellated beam becomes popular in building structural as beam members. This is due to several advantages of castellated beam such as increased depth without any additional mass, passing the underfloor service ducts without changing of story elevation. However, the presence of holes can develop various local effects such as local buckling, lateral torsional buckling caused by compression force at the flange section of the steel beam. Many studies have investigated the failure mechanism of castellated beam and one technique which can prevent the beam fall into local failure is the use of reinforced concrete slab as lateral support on castellated beam, so called composite castellated beam. Besides of preventing the local failure of castellated beam, the concrete slab can increase the plasticity moment of the composite castellated beam section which can deliver into increasing the ultimate load of the beam. The aim of this numerical studies of composite castellated beam on certain loading condition (monotonic quasi-static loading). ABAQUS was used for finite element modelling purpose and compared with the experimental test for checking the reliability of the model. The result shows that the ultimate load of the composite castellated beam reached 6.24 times than the ultimate load of the solid I beam and 1.2 times compared the composite beam.

Investigation of sub-critical fatigue crack growth in FRP/concrete cohesive interface using digital image analysis

The cohesive stress transfer during the sub-critical crack growth associated with the debonding of FRP from concrete under fatigue loading is experimentally investigated using the direct shear test set-up. The study focused on high-amplitude/low-cycle fatigue. The fatigue sub-critical crack growth occurs at a load that is smaller than the static bond capacity of the interface, obtained from monotonic quasi-static loading, and is also associated with a smaller value of the interfacial fracture energy. The strain distribution during debonding is obtained using digital image correlation. The results indicate that the strain distribution along the FRP during fatigue is similar to the strain distribution during debonding under monotonic quasi-static loading. The cohesive crack model and the shape of the strain distribution adopted for quasi-static monotonic loading is indirectly proven to be adequate to describe the stress transfer during fatigue loading. The length of the stress transfer zone during fatigue is observed to be smaller than the cohesive zone of the interfacial crack under quasi-static monotonic loading. The strain distribution across the width of the FRP sheet is not altered during and by fatigue loading. A new formulation to predict the debonding crack growth during fatigue is proposed.

Quasi-static mechanical behaviour of a double-shear single dowel wood connection

Results of a double-shear single dowel wood connection tested under monotonic quasi-static loading, according to the EN26891 standard, are discussed in this paper. The Pinus pinaster species, which is one of the most important Portuguese woods, was used in this study. The initial joint slip modulus, the ultimate strength and the ductility are evaluated and compared with values given by the Eurocode 5. Embedding tests are also carried out according to the EN383 standard. The resulting data is used to predict the joint slip modulus, through a proposed analytical model supported by statistical regression analysis data. Finally, a three dimensional finite element model of the wood connection was built and calibrated using available experimental data. This model can be applied to evaluate accurate values for the joint initial slip modulus.

Microvoid Damage Model with Material Dilation for Ductile Fracture

A constitutive model that incorporates material dilation and the concept of continuum damage mechanics is developed to predict ductile fracture of steel under monotonic quasi-static loading due to microvoids. In this model, damage is assumed to be isotropic and is a function of the state of stress and the plastic strain increment. Material dilation is assumed to vary with the state of damage. Fracture occurs when the damage limit is reached. Parameters for the model are calibrated using data obtained from tension coupon tests. The constitutive model and the process used to determine its parameters are described. Analyses have been carried out to illustrate the effect of incorporating material dilation. The model is able to closely predict the load versus deformation curve of the tension test. Additional test data required for verifying the model have also been outlined.

Dual-Stiffness Sensor for Damage Detection,Localization, and Prognostics.

The concept of a dual stiffness sensor that measures material degradation at the micromechanics scale and introduces damage variables to reflect average material degradation at a macromechanics scale is developed. The idea of a mechanical multifunctional dual stiffness sensor for in situ real-time stiffness and energy density measurements is motivated by Eshelby’s equivalent inclusion theorem. A complete analytical derivation is presented and the use of a dual stiffness/energy sensor to diagnose damage and to determine the remaining life of structures is evaluated. A numerical verification using finite element analysis is presented, and the results indicate that the sensor can be used for diagnostics and prognostics of structures. A distributed array of sensors is used to determine the onset and location of damage. Experimental results presented for uniaxial experimental tests under monotonic quasi-static loading conditions indicate that the concept can easily be implemented. For a sensor pair of known geometry and material properties, the Eshelby tensors are independent of the host: A methodology was thus developed to detect material properties of different hosts and was used to predict accurately elastic material properties of diverse materials.