Plastic Energy Dissipation Research Articles

Mass irregularity effect on seismic response of moment‐resisting steel frame by nonlinear time history analysis using force analogy method

SummaryNonlinear time history analysis (NTHA) is widely considered to be the most accurate and robust method of seismic analysis and, when performed with force analogy method (FAM), can result in significant reduction in computational time, as compared to the conventional displacement‐based finite element (FE) solution technique. Taking this advantage of efficient FAM, this paper investigates the effects of location (along building height) and intensity (150–225%) of single‐floor mass irregularity on seismic response of mid‐rise moment‐resisting steel frames. Three building heights (6, 8, and 10 storeys) have been considered, and the analysis results are presented in the form of floor displacements, storey drift ratio, and plastic energy dissipation. Based on the analysis, it has been observed that critical location (for the maximum seismic response) of mass‐irregular floor corresponds to the level that exhibited the maximum seismic response (i.e., storey drift ratio) in the reference mass‐regular frame. Further, criticality of the irregular frame to seismic excitation has been found to decrease when mass‐irregular floor moves towards the top of the building. The criticality of the irregular frame has been found to increase with the increase in mass‐irregular intensity. Collapse of the irregular frame has been seen to initial first near the storey level where mass‐irregular floor is located.

Preliminary Assessment of the Seismic Vulnerability of Three Inclined Bell-towers in Ferrara, Italy

ABSTRACT Three inclined historical masonry towers, located in the city of Ferrara (North-East region of Italy), are analyzed under seismic loads employing advanced numerical models. This study provides a critical review on the conservation state, present vulnerabilities, influence of peculiar structural features, and future need for strengthening interventions. Three scenarios were performed, mimicking the seismic severity of earthquakes for three different return periods: 50y, 200y, and 500y. The mechanical properties adopted for the models were extracted by tuning the dynamic response of the models with ambient vibrations test results. A concrete damage plasticity material, with a simplified multilinear softening in both tension and compression, is here adopted. Three parameters are investigated for an insight into the seismic performance estimation: (i) the damage pattern, (ii) the dissipated plastic energy, and (iii) the top displacement. Nonlinear dynamics simulations show the dissemination of structural damages for relatively low magnitude of ground acceleration, where clear failure mechanisms are prone to be activated. The present case studies exhibit unsymmetrical failure mechanisms due to the geometrical features, favoring the crack propagation in in-tension sidewalls, or stability loss of compressed walls. From a preliminary estimation of their seismic vulnerability, it is deduced that a relatively high risk is still present.

Thermo-Mechanical Stress Comparison of a GaN and SiC MOSFET for Photovoltaic Applications

Integrating photovoltaic applications within urban environments creates the need for more compact and efficient power electronics that can guarantee long lifetimes. The upcoming wide-bandgap semiconductor devices show great promise in providing the first two properties, but their packaging requires further testing in order to optimize their reliability. This paper demonstrates one iteration of the design for reliability methodology used in order to compare the generated thermo-mechanical stress in the die attach and the bond wires of a GaN and SiC MOSFET. An electro-thermal model of a photovoltaic string inverter is used in order to translate a cloudy and a clear one-hour mission profile from Arizona into a junction losses profile. Subsequently, the finite element method models of both devices are constructed through reverse engineering in order to analyze the plastic energy. The results show that the plastic energy in the die attach caused by a cloudy mission-profile is much higher than that caused by a clear mission-profile. The GaN MOSFET, in spite of its reduced losses, endures around 5 times more plastic energy dissipation density in its die attach than the SiC MOSFET while the reverse is true for the bond wires. Potential design adaptations for both devices have been suggested to initiate a new iteration in the design for reliability methodology, which will ultimately lead to a more reliable design.

Numerical and experimental response of FSSW of AA5052-H32/epoxy/AA5052-H32 sandwich sheets with varying core properties

The present work aims to assess the joint behaviour of friction stir spot welded sandwich sheets by changing the quality of the epoxy core layer. Lab scale experiments and numerical simulations are conducted for the purpose. The core property is altered by varying hardener to resin (h/r) ratio within a suitable range. Joint mechanical performance and joint characterization are evaluated from experiments. Cohesive zone modelling has been incorporated in Abaqus to monitor the hook formation and interface delamination, which is not performed until now in literature. The core quality influences the behaviour of sandwich sheet and hook geometry significantly. Desired h/r ratio is also evaluated from such results, and FSSW is found advantageous at some h/r ratios. The failure mode is independent of h/r ratio and loading conditions. The final joint shape and hook geometry obtained from FE simulations agree well with that of from experiments. Cohesive zone modelling helped in accurate prediction of delamination, and without it, the hook geometry and plastic energy dissipation predictions are approximated. It has been suggested to incorporate cohesive zone model during FE simulations to have a realistic prediction of sandwich joint performance.

Elasto-Plastic Impact on Auxetic/Metal Foams

AbstractWe investigate the normal impact of a rigid sphere on a half-space of elasto-plastic auxetic/metal foam using the finite element method. The dependence of the coefficient of restitution, peak force, maximum displacement, and contact duration on the yield strain, impact velocity, and elastic and plastic Poisson’s ratio is analyzed. For a given elastic Poisson’s ratio, the coefficient of restitution generally decreases with an increase in the plastic Poisson’s ratio and impact velocity. When the plastic Poisson’s is maintained constant, the coefficient of restitution increases with an increase of the elastic Poisson’s ratio. These trends are explained using plastic energy dissipation. The energy dissipation trends are further investigated by decomposing it into deviatoric and hydrostatic parts. For a given impact velocity, the peak force is relatively insensitive to most of the elastic and plastic Poisson’s ratio combinations. We also show that for the cases where the elastic and plastic Poisson’s ratios are equal, the coefficient of restitution is relatively insensitive to their actual values. These findings can guide researchers to identify the right elastic and plastic Poisson’s ratio combinations so that lattice materials with exceptional energy absorbing capacity can be designed using topology optimization.

Damage Assessment and Progressive Collapse Resistance of a Long-Span Prestressed Double-Layer Composite Torsional Reticulated Shell

Long-span prestressed double-layer composite torsional reticulated shells have beautiful shapes, which make them a solution widely applied in public buildings requiring long-span structures, such as airports and stadiums. However, once the progressive collapse occurs, this will cause serious issues. There are few studies on the damage assessment of long-span spatial structures under accidental loads. This paper proposes a new dynamic damage evaluation index that takes into account the displacement and the cumulative plastic energy dissipation to evaluate the damage of the long-span prestressed double-layer composite torsional reticulated shell. Sleeve structures were applied to the long-span space structures to study their control effect on structural damage. The equivalent load transient unloading method was used to analyze the dynamic time history of the structure. Results show that the structure suffered severe damage and progressive collapse failure after removing four nodes at different positions near the supports. In the position where the plastic hinges first appear and the position with the maximum displacement, the sleeve structures have a poor damage control effect on the structure. Arranging the two sleeve structures in the position of maximum stress, the damage of the structure can be controlled, thus reducing the severe damage and progressive collapse failure to basic intact damage.

A simplified method to efficiently design steel fenders subjected to vessel head-on collisions

Steel fenders have been widely used to protect bridges from vessel collisions because of their relatively large plastic deformability and energy dissipation capacity. In the design of a steel fender, detailed finite element (FE) models are usually employed. However, detailed FE analysis involves complicated modeling and substantial computation time. This method is often not applicable, particularly during preliminary design iterations. For this reason, a simplified analytical method was developed in this paper with the aim to efficiently design steel fenders under vessel collisions. For primary individual members of steel fenders, the deformation mechanisms and models as well as participations during various collision scenarios were discussed in detail. By combining the contributions of primary members, a general analytical procedure was presented to rapidly estimate the force-deformation relationship of steel fenders under various bow impacts. For the fixed and floating steel fenders, several collision scenarios were simulated by FE models to verify the accuracy of the developed analytical method. The crushing resistances and energy dissipation capacities estimated by the developed analytical method were in good agreement with those obtained from the FE simulations. Based on the analytical method, an energy-based design approach was proposed for the efficient design of steel fenders. The developed design approach was demonstrated to be capable of predicting the crush depth and peak impact force of a steel fender with good accuracy.

Influence of the constraint condition of column ends on seismic performance of a novel prefabricated concrete frame beam – An experimental and numerical investigation

A novel prefabricated concrete frame beam with an innovative assembling pattern is developed and studied in this paper, and it is characterized by simple operation, economical and good fault-tolerance performance. Quasi-static tests were carried out on one monolithic beam and two PC beams to investigate the influence of the constraint condition of column ends on the hysteretic behavior of the proposed beams. Analyses and comparisons were conducted in terms of the cracking propagation pattern, the failure mode, the load-bearing capacity, the beam ductility, the beam stiffness and the plastic energy dissipation ability. It is concluded that the constraint condition of column ends had a great influence on the failure mode of the proposed beams. Furthermore, the PC frame beam with restricted column ends had relatively higher load-bearing capacity and stiffness, slightly lower ductility and energy dissipation ability compared with that of PC frame beam with free column ends. In general, the seismic performance of the proposed PC beams was similar with that of the monolithic one under the same constraint condition of column ends. Note that the results of the evolution of the crack width versus the cyclic load were obtained and especially a significant increasing of the crack width after the beam yielded. Finite element analysis method was introduced to conduct a further analysis of the PC beams. The parametric analysis results recommended a reasonable and relatively small stirrup spacing for application of the proposed novel PC frame beams.

An ETA-PDE Method for the Fragility Analysis of Concrete Dam

A nonlinear damage ETA-PDE method is proposed for the fragility analysis of concrete dam. The endurance time analysis (ETA) method and the generalized probability density evolution (PDE) method are constructed by optimization and the method of lines (MOL) algorithm especially for the randomness of ground motion. Then, by integrating the ETA method and generalized PDE method, a nonlinear damage ETA-PDE method is established. To verify the applicability and reliability of the proposed ETA-PDE method, by using the tensile damage model, the nonlinear damage dynamic calculation and the fragility analysis are carried out for the Koyna concrete gravity dam. The results show the proposed PDE method can capture details of the probability density distribution for the fragility indicators (such as the plastic dissipation energy, the damage dissipation energy, the damage volume and so on). The proposed ETA-PDE method has special advantages on the calculating scale and solving probability density. Thus, it is suitable for practical engineering applications.

Mechanical behaviour of graded chemically bonded ceramic coating

ABSTRACT To investigate the mechanical behaviour of graded chemically bonded ceramic coating, four types of ceramic coatings were prepared in this study, and a graded coating was designed using the four coatings sorted by hardness. A finite element simulation was performed to observe the mechanical properties of the graded coating. The results revealed that the effective hardness of the graded coating decreased with increasing load; however, it was found to be higher than that of the fourth layer. In addition, the performance of the graded coating was good in terms of the plastic dissipation energy, and it changed the location of plastic deformation from the middle to the inside layer of the coating. Additionally, the graded structure was found to decrease the Mises stress and degree of the sudden increase in the Mises stress on the interlayer of the coating and substrate, which improved their bond strength.

Long duration and frequent, intense earthquakes: Lessons learned from the 19 September 2017 earthquake for Mexico City’s resilience

The accumulation of plastic deformations during an intense earthquake may cause structural failures at deformations significantly smaller than those that can be developed under monotonic load. However, there is evidence that, under certain circumstances, the response of a single parameter may not be a good indicator of structural damage. Likewise, most of the seismic regulations, including the Mexican standards, establish their criteria considering the occurrence of strong earthquakes with a very little probability of occurrence, but do not consider if intense earthquake affects the building frequently and, therefore, cumulative damage due to the occurrence of several earthquakes during the life span of the structure is not taken into account explicitly. This cumulative damage is especially important in places like Mexico City, where intense and long-duration earthquakes occur every 10–20 years. To study the issues that Mexico City must face to increase its seismic resilience, in this article, we present an analysis of the dissipated plastic energy demands in Mexico City during the earthquake of 19 September 2017, and the cumulative damage due to recent intense earthquakes that affect the city.

Ductile damage and fragmentation of highly porous γ-alumina under multi-point crushing test

Mechanical behavior of highly porous alumina catalytic supports is investigated through a non-conventional approach consisting in a multi-point crushing of individual cylindrical extrudates. A ductile behavior characterized by irreversible deformation and fragmentation phenomena is observed and pointed out by experimental load-displacement curves. SEM fractographies of the fragments collected after the tests confirm the presence of dense micro-cracking and of local deformations under contact zones. A Finite Element analysis of the test shows that a Drucker-Prager strength criterion associated with a perfectly plastic flow rule mimics the global damageable behavior of the specimen under the multi-point crushing test. A correlation is proposed between the evolution of the mass of fine fragments and the plastic energy dissipation.

In situ investigation into temperature evolution and heat generation during additive friction stir deposition: A comparative study of Cu and Al-Mg-Si

Additive friction stir deposition is an emerging solid-state additive manufacturing technology that enables site-specific build-up of high-quality metals with fine, equiaxed microstructures and excellent mechanical properties. By incorporating proper machining, it has the potential to produce large-scale, complex 3D geometries. Still early in its development, a thorough understanding of the thermal process fundamentals, including temperature evolution and heat generation mechanisms, has not been established. Here, we aim to bridge this gap through in situmonitoring of the thermal field and material flow behavior using complementary infrared imaging, thermocouple measurement, and optical imaging. Two materials challenging to print via beam-based additive technologies, Cu and Al-Mg-Si, are investigated. During additive friction stir deposition of both materials, we find similar trends of thermal features (e.g., the trends of peak temperature TPeak, exposure time, and cooling rate) with respect to the processing conditions (e.g., the tool rotation rate Ω and in-plane velocity V). However, there is a salient, quantitative difference between Cu and Al-Mg-Si; TPeak exhibits a power law relationship with Ω/V in Cu but with Ω2/V in Al-Mg-Si. We correlate this difference to the distinct interfacial contact states that are observed through in situ material flow characterization. In Cu, the interfacial contact between the material and tool head is characterized by a full slipping condition, so interfacial friction is the dominant heat generation mechanism. In Al-Mg-Si, the interfacial contact is characterized by a partial slipping/sticking condition, so both interfacial friction and plastic energy dissipation contribute significantly to the heat generation.

Numerical investigation of mechanical behavior of crack tip under mode I and mixed-mode I-II fatigue loading at negative load ratios

The mechanical behavior of crack tip under mode I and mixed-mode I-II fatigue loading for commercial pure titanium at negative load ratios are carried out by finite element method in this paper. The effects of maximum fatigue load, load ratio, loading angle and normalized crack length on the mechanical behavior of crack tip are discussed. The change of mechanical behavior of crack tip is analyzed through the evolution of strain energy. The results show that the increase of maximum fatigue load and crack length increase the plastic strain accumulation at crack tip in mode I fatigue crack growth (FCG), which causes the crack tip release more fracture energy to drive crack growth and affect the distribution of stress-strain field. The decrease of load ratio also increases the plastic strain accumulation and the plastic energy dissipation at crack tip. In mixed-mode I-II FCG, the larger loading angle increase the resistance of crack deflection and cause more plastic strain accumulation at crack tip. After the crack deflects, the crack growth increases the crack tip plastic zone and the morphology of plastic zone changes continuously, which cause the crack growth path move away from the mode I crack growth direction. Different loading angles produce different crack growth paths, which deviates from mode I crack growth direction with the increase of loading angle.

The Sensitivity of an Electro-Thermal Photovoltaic DC–DC Converter Model to the Temperature Dependence of the Electrical Variables for Reliability Analyses

The operational expenditures of solar energy are gaining attention because of the continuous decrease of the capital expenditures. This creates a demand for more reliable systems to further decrease the costs. Increased reliability is often ensured by iterative use of design for reliability. The number of iterations that can take place strongly depends on the computational efficiency of this methodology. The main research objective is to quantify the influence of the temperature dependence of the electrical variables used in the electro-thermal model on the reliability and the computation time. The influence on the reliability is evaluated by using a 2-D finite elements method model of the MOSFET and calculating the plastic energy dissipation density in the die-attach and the bond wire. The trade-off between computation time of the electro-thermal model in PLECS (4.3, Plexim, Zurich, Switzerland) and generated plastic energy accuracy obtained in COMSOL (5.3, COMSOL Inc., Burlington, MA, USA) is reported when excluding a certain temperature dependence. The results indicate that the temperature dependence of the input and output capacitors causes no change in the plastic energy dissipated in the MOSFET but does introduce the largest increase in computation time. However, not including the temperature dependence of the MOSFET itself generates the largest difference in plastic energy of 10% as the losses in the die are underestimated.

Improving the Blast Resistance of Large Steel Gates-Numerical Study.

Blast resistant gates/doors are essential for sensitive infrastructure, such as embassies, ministries, or parliaments. Lightweight gates equipped with ‘energy absorbing systems’ have better operational performance than the traditional costly and bulky design. Graded auxetic structures have not yet been used as potential passive damping systems in the supporting frame of blast resistant gates. Consequently, this study tries to test if a uniaxial graded auxetic damper (UGAD) proposed by the authors in a recent article, namely the development of a new shock absorbing UGAD, could maintain a 3000 mm × 4500 mm steel gate operable after high blast peak reflected overpressure of 6.6 MPa, from 100 kg TNT at 5 m stand-off distance. The blast-induced response of the gate was assessed, with and without the proposed UGAD, using Abaqus/Explicit solver. Results showed that the attachment of the proposed UGAD to the gate led to a dramatic decrease in permanent deformations (a critical factor for gate operability after a blast event). Hence, a lighter, more economical gate (with 50% reduction in mass) was required to satisfy the operability condition. In addition, 49% of peak reaction forces were diminished, that have a direct impact on the supporting frame. Moreover, the results revealed that, in the numerical model, 56% of the achieved plastic dissipation energy was from the UGADs, and 44% from the gate. The outcomes of this research may have a positive impact on other sectors beyond academia, such as industry, economy, and public safety.

Modeling of Plastic Deformation Based on the Theory of an Orthotropic Cosserat Continuum

In the paper, the plastic deformation of heterogeneous materials is analyzed by direct numerical simulation based on the theory of an elastic-plastic orthotropic Cosserat continuum, with the plasticity condition taking into account both the shear and rotational mode of irreversible deformation. With the assumption of a block structure of a material with elastic blocks interacting through compliant plastic interlayers, this condition imposes constraints on the shear components of the asymmetric stress tensor, which characterize shear, and on the couple stresses, which irreversibly change the curvature characteristics of the deformed state of the continuum upon reaching critical values. The equations of translational and rotational motion together with the governing equations of the model are formulated as a variational inequality, which correctly describes both the state of elastic-plastic deformation under applied load and the state of elastic unloading. The numerical implementation of the mathematical model is performed using a parallel computing algorithm and an original software for cluster multiprocessor systems. The developed approach is applied to solve the problem of compressing a rectangular brick-patterned blocky rock mass by a rough nondeformable plate rotating with constant acceleration. The effect of the yield stress of the compliant interlayers on the stress-strain state of the rock mass in shear and bending is studied. The field of plastic energy dissipation in the rock mass is analyzed along with the fields of displacements, stresses, couple stresses, and rotation angle of structural elements. The obtained results can help to validate the hypothesis about the predominant effect of curvature on plastic strain localization at the mesolevel in microstructural materials.

Analytical modeling of contact mechanics of helical gear tooth by considering surface roughness effects

Release of metal debris from a pair of gear teeth is a consequence of their contact. Any excessive metal debris can lead to the onset of fatigue and failure. This paper aims to derive a contact mechanics-based model to obtain the energy absorption of helical gear teeth. The proposed model includes the roughness effect of teeth contact surfaces. The mean value of the asperity summit curvature, the standard deviation of the asperity height distribution and the area density of the asperity height distribution are the three statistical parameters that describe the micron-scale surface roughness. An explicit approximation is obtained to relate the contact load and the minimum surface separation and to estimate the energy loss. Then an analytical expression is derived for the plastic energy dissipation per cycle as a function of plasticity index for gear teeth. The proposed function can be applied in the design of gears by engineers and manufacturers. Additionally, a pertinent lumped mass at the area of interaction is assumed to describe the contact frequency and damping ratio using a nonlinear dynamic model.

The effect of bond-line thickness on fatigue crack growth rate in adhesively bonded joints

The effect of adhesive thickness on fatigue crack growth in an epoxy film adhesive (FM94) was investigated, using a combination of experiments and numerical modelling. For the range of thicknesses investigated an increased thickness led to an increased crack growth rate. It was found that the energy required per unit of crack growth did not depend on the adhesive thickness. In contrast, the energy available for crack growth does depend on the adhesive thickness.The numerical analysis confirms that the energy required per unit crack growth is not sensitive to the adhesive thickness, but that the plastic energy dissipation increases with the thickness. The experimental results imply that this increase of plasticity has an anti-shielding effect, as the crack growth rate is increased.

Embrittlement induced fracture behavior and mechanisms of perfluorosulfonic-acid membranes after chemical degradation

Chemical and mechanical degradations of perfluorosulfonic-acid membranes are two factors contributing to the reduced durability of fuel cells. While the mechanisms of isolated chemical or mechanical degradation are extensively investigated, the impact of chemical degradation on mechanical degradation is not fully understood. In this paper, the fracture behavior of Nafion 212 membranes with different chemical degradation levels are investigated. To characterize the degradation level and probe the molecular origins of chemical degradation, fluoride release, Fourier-transformer infrared spectra, conductivity and swelling behavior are measured. It is found that chemical degradation causes predominant loss of side-chains. A transition from ductile to brittle fracture is observed with increasing degradation level. In addition, the cross-sections are examined to link fracture behavior with microstructure changes. While the decreased fracture toughness is attributed to reduced mechanical properties such as Young's modulus and break strain, the decreased crack propagation resistance is ascribed to reduced plastic zone size ahead of crack tip, which reduces the plastic energy dissipation. These findings not only provide new mechanical dataset of degraded membranes for performance and durability modelling to take into account of chemical degradation effect but also improve the understanding of membrane durability.