Elastic Energy Dissipation Research Articles

Transient and steady state viscoelastic crack propagation in a double cantilever beam specimen

Crack growth in viscoelastic materials is understood with the use of cohesive models, or steady state theories which focus on viscoelastic dissipation. We consider a double cantilever beam (DCB) specimen under a remote constant pure moment, which is initially suddenly applied to the beams. It is shown that the response to the applied moment rapidly reaches a steady state in terms of crack propagation speed. In contrast, it is shown that the external work rate, contributing to fracture energy, stored elastic energy and viscous dissipation, has a transient that possibly lasts a significantly longer time. The dissipation rate increases with speed for a standard material, reaching a limit governed by the ratio of instantaneous to relaxed modulus. However, the initial dissipation rate at low crack propagation speeds can be orders of magnitude larger than the latter limit, and depends on the ratio between the initial crack size and the fracture process zone size, a regime which we define ultratough. For thin beams, we do not find any evidence, even in the steady state, of the dissipation-based theories’ suggestion of a reduced maximum load and then of an unstable regime of decreasing load with speed.

Energy dissipation and shock isolation using novel metamaterials

Dissipating kinetic energy from shock and vibration is an urgent requirement for various applications in aerospace to mechanical engineering. This paper proposes a series of innovative metamaterials with planar and cylindrical patterns for elastic energy dissipation and shock isolation. The planar unit cell with two axes of reflectional symmetry mainly consists of two V-shaped regions, four identical right triangle regions, and narrow regions. The stereometric and cylindrical unit cells are obtained through rotating and convolving methods. The mechanics of energy dissipation and shock isolation are systematically investigated with finite element analysis (FEA), and experiments. Results show that various mechanical responses of unit cells are obtained through tailoring combined geometric parameters and additional boundary conditions, and the planar unit cell has stronger bistability than the cylindrical one. Then, the designed multilayers metamaterials exhibit considerable energy dissipation via the snap-through induced hysteric force-displacement behaviors, whose performances are influenced by geometric parameters and the number of layers. Lastly, the designed metamaterials could effectively suppress the acceleration responses via the snap-through behaviors induced by elastic instability. The shock response process and corresponding deformation mechanics are investigated experimentally and numerically. The designed metamaterials have potential in shock and vibration engineering.

Experimental Study on Triaxial Compressive Mechanical Properties of Polypropylene Fiber Coral Seawater Concrete.

In order to study the mechanical properties of polypropylene fiber all-coral seawater concrete in triaxial compression, 36 specimens were developed and constructed for triaxial compression load testing employing confining pressure value (0, 6, 12, 18 MPa) and polypropylene fiber admixture (1 kg·m−3, 2 kg·m−3, 3 kg·m−3) as variation parameters. The test observed the failure mode of the specimen and obtained the stress–strain curve of the whole process of its force damage failure. An in-depth analysis of polypropylene fiber all-coral seawater concrete’s peak stress, peak strain, initial elastic modulus, axial deflection, energy dissipation, ductility, and damage evolution process was carried out based on the experimental data. The test findings indicated that the best effect on the deformation properties of polypropylene fiber all-coral seawater concrete is obtained when 3 kg·m−3 of polypropylene fiber is blended. Under triaxial compression, the correct number of polypropylene fibers may significantly enhance the peak stress, peak strain, ductility, and elastic modulus of polypropylene fiber all-coral seawater concrete, therefore enhancing the brittle characteristics of coral concrete. During the triaxial surround pressure test, the confining pressure value and polypropylene fiber coupling effect delayed the appearance of initial damage in polypropylene fiber complete coral seawater concrete specimens, slowed the development of damage, and reduced the degree of damage to the specimens.

Fracture Toughness and Blocking Force of Temperature-Sensitive PolyNIPAAm and Alginate Hybrid Gels.

In the field of actuator materials, hydrogels that undergo large volume changes in response to external stimuli have been developed for a variety of promising applications. However, most conventional hydrogels are brittle and therefore rupture when they are stretched to moderate strains (~50%). Thus, gels to be used for actuators still require improved mechanical properties and actuation performance. In this study, we synthesized a tough and thermo-sensitive hydrogel with a large actuation force by forming interpenetrating networks between covalently crosslinked poly(N-isopropylacrylamide) and ionically crosslinked alginate. Poly(N-isopropylacrylamide) was used as a thermo-sensitive actuation material, and alginate was found to enhance the mechanical properties of the hydrogels. Due to the enhanced elastic modulus and energy dissipation in the hybrid gel, the toughness was increased by a factor of 60 over that of pure PNIPAAm gel. Further, based on the results showing that the hybrid gel exhibits an actuation force that is seven times higher than that of pure PNIPAAm gel, the hybrid gel is more applicable to real actuators.

Finite Element Analysis of the Ballistic Impact on Auxetic Sandwich Composite Human Body Armor.

In this study, the ballistic impact behavior of auxetic sandwich composite human body armor was analyzed using finite element analysis. The auxetic core of the armor was composed of discrete re-entrant unit cells. The sandwich armor structure consisted of a front panel of aluminum alloy (Al 7075-T6), UHMWPE (sandwich core), and a back facet of silicon carbide (SiC) bonded together with epoxy resin. Numerical simulations were run on Explicit Dynamics/Autodyne 3-D code. Various projectile velocities with the same boundary conditions were used to predict the auxetic armor response. These results were compared with those of conventional monolithic body armor. The results showed improved indentation resistance with the auxetic armor. Deformation in auxetic armor was observed greater for each of the cases when compared to the monolithic armor, due to higher energy absorption. The elastic energy dissipation results in the lower indentation in an auxetic armor. The armor can be used safely up to 400 m/s; being used at higher velocities significantly reduced the threat level. Conversely, the conventional monolithic modal does not allow the projectile to pass through at a velocity below 300 m/s; however, the back face becomes severely damaged at 200 m/s. At a velocity of 400 m/s, the front facet of auxetic armor was destroyed; however, the back facet was completely safe, while the monolithic panel did not withstand this velocity and was completely damaged. The results are encouraging in terms of resistance offered by the newly adopted auxetic armor compared to conventional monolithic armor.

Seismic performance of circular RC columns strengthened in flexure using NSM reinforcement and externally bonded BFRP sheets

To study the seismic performance and recoverable capacity of reinforced concrete (RC) columns strengthened in flexure by employing different kinds of reinforcing materials, six 1/4.7 scale circular specimens including one control, which were strengthened by combining near-surface-mounted (NSM) reinforcement with externally bonded basalt fiber reinforced polymer (BFRP) sheets, were designed to investigate the seismic behavior and tested under the constant axial compressive load and lateral cyclic loading. The experimental parameters included different types of NSM reinforcing materials (carbon or basalt fiber reinforced polymers, steel), confinement conditions (no wrapping and wrapping), and different types of externally bonded BFRP sheets (unidirectional and bidirectional BFRP sheets). The results demonstrate that.the scheme of NSM reinforcement is an effective solution toward enhancing the flexural capacity and the recoverable performance of RC columns. Compared to the other strengthening schemes, the scheme (column C3-10B-4U) combining NSM BFRP bars with externally bonded BFRP unidirectional sheets is most effective in increasing the elastic energy dissipation capacities and also enhancing the ductility and deformation capacity of strengthened columns, but do not change the stiffness significantly. Furthermore, the results indicate that the residual displacement of the column C3-10B-4U is the smallest of all columns under the same applied displacement and thereby the recoverability of the column C3-10B-4U was better than that of the other strengthened columns.

Size-Dependent Chemomechanical Failure of Sulfide Solid Electrolyte Particles during Electrochemical Reaction with Lithium.

The very high ionic conductivity of Li10GeP2S12 (LGPS) solid electrolyte (SE) makes it a promising candidate SE for solid-state batteries in electrical vehicles. However, chemomechanical failure, whose mechanism remains unclear, has plagued its widespread applications. Here, we report in situ imaging lithiation-induced failure of LGPS SE. We revealed a strong size effect in the chemomechanical failure of LGPS particles: namely, when the particle size is greater than 3 μm, fracture/pulverization occurred; when the particle size is between 1 and 3 μm, microcracks emerged; when the particle size is less than 1 μm, no chemomechanical failure was observed. This strong size effect is interpreted by the interplay between elastic energy storage and dissipation. Our finding has important implications for the design of high-performance LGPS SE, for example, by reducing the particle size to less than 1 μm the chemomechanical failure of LGPS SE can be mitigated.

Adhesion strength of Tii_xCx – DLC multilayer nanocomposite thin films coated by ion-plasma deposition on martensitic stainless steel produced by selective laser melting followed by plasma-nitriding and burnishing

[Ti0.2C0.8/a-C]40 multilayer thin films composed of forty pairs of TiC and pure carbon layers were formed on a selective laser melted (SLM) martensitic stainless steel by means of ion-plasma deposition process. SLM steel was pre-treated by one of the two following schemes: (1) oil quenching from 1040°C followed by heating to 480°C for 4 hours and air cooling (HT), finish milling (FM); (2) HT, FM, ion-plasma nitriding followed by burnishing. Mechanical failure mode and critical load Lc for damaging the coatings were determined using linear scratch tests performed at linearly-increased normal force. Indentation by conical diamond tip were carried out in order to asses an elastic recovery and energy dissipation coefficient defined as the ratio of plastic to total deformation energy. The scratch test results showed that the post-processing of the substrate strongly influenced the failure mode of the coating and increased the critical load from 320 mN to 920 mN. Indentation revealed that nitriding and burnishing before coating deposition increase the elastic recovery of the [Ti0.2C0.8/a-C]40 coating-substrate system from 24% to 68%. The energy dissipation coefficient drops from 79% to 45%.

Cyclic behavior and reinforcement of moment-resisting bolted glulam joints with cracks

This paper experimentally explored the influence of cracks on cyclic behavior of moment-resisting bolted glulam joints, and investigated the strengthening of self-tapping screws and friction dampers. Under reversed cyclic loading, the failure modes and hysteresis curves of pre-cracked specimens have been presented and analyzed in this paper. It was found that initial cracks not only led to the decrease in the moment capacity and elastic stiffness, but also impaired the ductility behavior and energy dissipated capacity of bolted glulam joints. The ductility ratio and accumulated energy dissipation can be reduced by 30% and 60%, respectively. With the installation of self-tapping screws and friction dampers, significant enhancement was observed in the above mentioned mechanical parameters of pre-cracked bolted joints. The elastic stiffness and energy dissipation are improved by 144% and 613%, respectively. Further, an analytical model is applied to calculate moment capacity of strengthened bolted joints and validated by experimental results.

Investigation on Pore-Fracture of Coal and Its Influence Mechanism on Tensile Failure Behavior of Coals with Bursting Proneness

Both computed tomography (CT) and notched semicircular bend (NSCB) tests are performed for coals with high and medium bursting proneness to extract the scientific expression of pore-fracture and its influence mechanism on the tensile failure behavior. The acoustic emission (AE) parameters in the sample during loading and failure are monitored, and the influence mechanism of pore-fracture on tensile failure behavior of coal is analyzed. The result illustrates that the spatial distribution feature of the pore-fracture in coals with high and medium bursting proneness is extremely different. The deformation and failure mode of the coals are affected by many factors, loading mode, notch depth and width, mechanical properties of matrix and minal, spatial distribution feature of pore-fracture, etc. The influence of primary pore-fracture in the coal on the extension and penetration of the secondary fracture could be divided into two types: bifurcation and promotion, which would cause different local damage in the sample and affect the final failure mode. The feature of acoustic emission parameters indicates that the deformation and failure process of a sample under loading could be divided into four stages: compaction stage, elastic deformation stage, displacement plastic growth stage, and post peak failure stage, which is the result of comprehensive action of many factors. The evolution process of secondary fracture is accompanied by the dissipation of elastic strain energy and the intensification of internal damage of coal, which reflects the failure process of coal.

Finite Element Analysis to Determine Stiffness, Strength, and Energy Dissipation of U-Shaped Steel Damper under Quasi-Static Loading

In seismic areas, the application of structural dampers becomes compulsory in the design of buildings. There are various types of dampers, such as viscous elastic dampers, viscous fluid dampers, friction dampers, tune mass dampers, yielding/ metallic dampers, and magnetic dampers. All damper systems are designed to protect structural integrities, control damages, prevent injuries by absorbing earthquake energy, and reduce deformation. This paper is a part of research investigating the behaviour of the U-shaped steel damper (as one type of metallic damper) that can be applied to the buildings in seismic areas. The dampers are used as connections between the roof and supporting structure, with the two general purposes. The first is to control the displacement of roof under an earthquake, and the second is to absorb seismic energy through the plasticity of some parts in dampers. If a strong earthquake occurs, the plasticity will absorb the seismic energy; therefore, heavy damage could be avoided from the roof’s mainframes. In this paper, several models of U-shaped steel dampers are introduced. Several parameters, such as elastic stiffness, maximum strength, and energy dissipation, are determined under two conditions. Firstly, static analysis of the proposed damper under variation of U-steel plate configurations, searching the model with more significant energy dissipation. Secondly, static analysis of the unsymmetrical and symmetrical damper under different loading directions. An in-house finite element program that involves both geometrical and material nonlinearities is developed as a problem solver. A quasi-static lateral loading is given to each model until one cycle of the hysteresis curve is reached (in the displacement range between -20 mm to +20 mm). The above parameters are calculated from the hysteresis curve. From the results, the behaviour of the U-steel damper can be described as follows. Firstly, increasing the energy dissipation in the lateral direction can be done by increasing the lateral stiffness of the damper. However, it can reduce the maximum elastic deformation of the damper. Secondly, under the random direction of loading, a symmetrical shape can increase the energy dissipation of the damper.

Experimental Study and Analysis on Rotational Behavior of Bamboo Scrimber Beam-to-Column Bolted Connections

This paper studies the rotational behavior of beam-to-column bolted connections in bamboo scrimber structures. Three types of beam-to-column connections, including bolted connections with outer-clamping steel plates, bolted connections encased with T-shaped steel plates, and bolted connections encased with double L-shaped steel plates, were designed and tested under monotonic or reversed cyclic loads. The influence of bolt arrangement on the mechanical properties was also studied. Failure of the connections was mainly caused by cracking of the adhesive interface near the bolt at the tensile side of the beam, which was a weak point that needs further attention. The elastic stiffness, capacities, ductility coefficient, and energy dissipation capacity of the T-steel connections improved compared with the I-steel connections. The load-carrying capacities of the connections were calculated according to common standards. Results showed that for the I-, T-, and double L-steel connections, the different standards had different safety margins.

Research on Optimization of Coal Pressure Relief Borehole Parameters under High-Stress Conditions

Determining the parameters of boreholes drilled for relieving pressure in coal seams is the key preventing and controlling rock bursts in boreholes of large diameter. In this study, theoretical analysis, numerical simulation, literature research, and other analysis methods are applied to study the angles of elastic energy dissipation and stress transfer, the distribution law of the pressure relief area, and the areas of stress concentration, energy, stress, displacement, and plastic behavior of large-diameter pressure relief boreholes in coal seams under high-stress conditions. The results are then used to evaluate the relationship between large-diameter pressure relief boreholes and the borehole arrangement. The following results are obtained. (1) A large-diameter results in a large amount of elastic energy released by the surrounding coal, low residual elastic energy density, strong interaction between boreholes, large pressure relief range of the borehole, and high pressure relief efficiency. (2) The main evaluation factor of the borehole pressure relief effect is its thickness and stress concentration area; secondary evaluation is based on the areas of energy, displacement, stress, and plastic behavior. (3) Six evaluation index systems are established to evaluate the effects of borehole pressure relief, which are found to be the thicknesses of the borehole pressure relief area and stress concentration area, reduction degree of energy density, percentage of stress reduction, displacement, and penetration degree of the plastic area. (4) It is determined that when the diameters of the pressure relief boreholes are 100, 120, 180, and 200 mm, a single-row borehole arrangement is adopted; a three-pattern borehole arrangement is adopted with diameters of 140 and 160 mm. These research results can provide theoretical support in selecting reasonable borehole arrangements for pressure relief boreholes of different diameters.

Low Mechanical Loss TiO_{2}:GeO_{2} Coatings for Reduced Thermal Noise in Gravitational Wave Interferometers.

The sensitivity of current and planned gravitational wave interferometric detectors is limited, in the mostcritical frequency region around 100Hz, by a combination of quantum noise and thermal noise. Thelatter is dominated by Brownian noise: thermal motion originating from the elastic energy dissipation in the dielectric coatings used in the interferometer mirrors. The energy dissipation is a material property characterized by the mechanical loss angle. We have identified mixtures of titanium dioxide (TiO_{2}) andgermanium dioxide (GeO_{2}) that show internal dissipations at a level of 1×10^{-4}, low enough to provide improvement of almost a factor of 2 on the level of Brownian noise with respect to the state-of-the-art materials. We show that by using a mixture of 44% TiO_{2} and 56% GeO_{2} in the high refractive indexlayers of the interferometer mirrors, it would be possible to achieve a thermal noise level in line withthe design requirements. These results are a crucial step forward to produce the mirrors needed to meetthe thermal noise requirements for the planned upgrades of the Advanced LIGO (Laser Interferometer Gravitational-Wave Observatory) and Virgo detectors.

Investigation on the interaction between BRBs and the RC frame in BRB-RCF systems

Due to the different mechanical behavior of buckling-restrained braces (BRB) and reinforced concrete frames (RCF), their coupled work in dual structural systems (BRB-RCFs) is complicated, especially their earthquake responses. A series of structures with different numbers of stories and different story shear ratios equipped with BRBs were designed and tested in simulation. Static nonlinear pushover analysis and cyclic loading were simulated to investigate the interaction between BRBs and RCFs. The capacity curves, the story distributions of shear force, axial forces on the columns, strength and stiffness, lateral displacement, interstory drift ratios and hysteresis behavior were evaluated. Adding BRBs in a RCF was found to alter the story distribution of shear force and to significantly increase the axial demands on RC columns in BRB-braced bays. The yield strength, initial elastic stiffness and energy dissipation capacity of BRB-RCF structures are all greater than the sum of the contributions from the braces and the frames independently. That synergistic interaction cannot be ignored in design.

Elastic Properties and Energy Dissipation Related to the Disorder-Order Ferroelectric Transition in a Multiferroic Metal-Organic Framework [(CH3)2NH2][Fe(HCOO)3] with a Perovskite-Like Structure.

The elastic properties and the coupling of ferroelasticity with ferromagnetism and ferroelectricy are crucial for the development of multiferroic metal-organic frameworks (MOFs) with strong magnetoelectric coupling. Elastic properties and energy dissipation related to the disorder-order ferroelectric transition in [(CH3)2NH2][Fe(HCOO)3] were studied by differential scanning calorimetry (DSC), low temperature X-ray diffraction (XRD) and dynamic mechanical analysis (DMA). DSC result indicated the transition near 164 K. XRD showed the first-order structural transition from rhombohedral Rc to monoclinic Cc at ~145 K, accompanied by the disorder-order transition of proton ordering in the N–H…O hydrogen bonds in [(CH3)2NH2]+ as well as the distortion of the framework. For single crystals, the storage modulus was ~1.1 GPa and the loss modulus was ~0.02 GPa at 298 K. DMA of single crystals showed quick drop of storage modulus and peaks of loss modulus and loss factor near the ferroelectric transition temperature ~164 K. DMA of pellets showed the minimum of the normalized storage modulus and the peaks of loss factor at ~164 K with weak frequency dependences. The normalized loss modulus reached the maximum near 145 K, with higher peak temperature at higher frequency. The elastic anomalies and energy dissipation near the ferroelectric transition temperature are caused by the coupling of the movements of dimethylammonium cations and twin walls.

Large eddy simulations of turbulent planar jets of viscoelastic fluids

Direct numerical simulations and large-eddy simulations of turbulent planar jets are used to assess the distortion similarity (DSIM) model, recently developed by Ferreira et al. [“Large-eddy simulations of forced isotropic turbulence with viscoelastic fluids described by the finitely extensible nonlinear elastic rheological model with Peterlin's closure model,” Phys. Fluids 28, 125104 (2016)] for homogeneous turbulence, in the simulation of turbulent viscoelastic planar jets. Both a priori and a posteriori tests of the DSIM model are used and show that the several assumptions used in the development of the DSIM model hold well in inhomogeneous free turbulent viscoelastic flows, e.g., (i) the scale similarity of the subgrid-scale (SGS) polymer stretching and (ii) the local equilibrium of the elastic energy production and dissipation. The DSIM model for the SGS polymer stretching term, together with the dynamic Smagorinsky model, is able to reproduce well the flow structures and the classical one-point statistics of turbulent viscoelastic planar jets. The model should be equally able to simulate other free shear flows of viscoelastic fluids, e.g., wakes and mixing layers.

Novel low Ag-content Sn–Ag–Cu–Sb–Al solder alloys with enhanced elastic compliance and plastic energy dissipation ability by applying rotating magnetic field

The main scope of this research is to investigate the impact of rotating magnetic field (RMF) on the physical properties of the Sn–0.5Ag–0.5Cu–2.0Sb–0.1Al (SAC0505SbAl) solder alloy. The application of RMF during molten alloy cooling showed prominent effect on the morphology, thermal properties, and the consequent mechanical characteristics. It was shown that the dendritic morphology was changed from columnar dendrites to equiaxed grains with the application of RMF. In addition, RMF processing modified the eutectic phases in the alloy matrix. These notable modifications have resulted in a substantial increase in ductility (~ 30%) with a slight decrease in tensile parameters (UTS and YS). Such effects could enhance elastic compliance and plastic energy dissipation ability of solder alloys, which plays superbly fundamental function in drop-impact reliability. Differential scanning calorimetry (DSC) analysis reveals that significant decrease in pasty range (from 10.8 to 7.5 °C) and undercooling (from 13.1 to 9.0 °C) was attained after applying RMF. The stress exponent (n), the activation energy (Q), and deformation mechanism of the SAC0505SbAl alloy processed with and without RMF were discussed in detail. The obtained results are certainly expected to fill the knowledge gap about the behavior of these recently developed solder alloys under the effect of RMF that are potential alternatives as Pb-free interconnecting material in microelectronic packaging industry.

The effect of latent plasticity on the shape recovery of a shape memory vitrimer

The utility of covalent crosslinkers as permanent netpoints has enabled robust shape memory behaviour in shape memory thermosets (SMTs). Having this permanent crosslinked structure, alternatively, challenges the reprogramming of permanent shapes. The introduction of vitrimeric type dynamic chemistry into SMTs allows for reconfiguration of crosslinked network and thus reprogramming of permanent shapes. However, adding this adaptability/plasticity to the network could potentially affect the shape memory behaviour, especially when the shape programming is conducted at a temperature that activates the network plasticity as well. Herein, to address the potential influence of network plasticity, we studied the shape memory behaviour of a shape memory vitrimer (SMV) that possesses a low network activation energy (Ea) of 33 kJ/mol, which indicates a relatively high plasticity index during shape programming. As we found, there is a dependence of shape recovery on the shape-programming time: a longer programming time leads to a poorer shape recovery. This negative correlation results from the dissipation of stored elastic energy at local strained regions associated with shape programming. We further related the loss of elastic energy to the stress-relaxation that results from chain exchanges. Accordingly, the dependence can be analyzed with an analog of stress-relaxation model. We reasoned that this latent plasticity associated with dynamic chain exchanges is ubiquitous in SMVs, and so one needs to carefully evaluate the reprogramming temperature and time when performing shape memory studies on SMVs.

Increasing Fatigue Life of 09Mn2Si Steel by Helical Rolling: Theoretical-Experimental Study on Governing Role of Grain Boundaries.

The structure and mechanical properties of the 09Mn2Si high-strength low-alloyed steel after the five-stage helical rolling (HR) were studied. It was revealed that the fine-grained structure had been formed in the surface layer ≈ 1 mm deep as a result of severe plastic strains. In the lower layers, the “lamellar” structure had been formed, which consisted of thin elongated ferrite grains oriented in the HR direction. It was shown that the five-stage HR resulted in the increase in the steel fatigue life by more than 3.5 times under cyclic tension. The highest values of the number of cycles before failure were obtained for the samples cut from the bar core. It was demonstrated that the degree of the elastic energy dissipation in the steel samples under loading directly depended on the area of the grain boundaries as well as on the grain shapes. The fine-grained structure possessed the maximum value of the average torsional energy among all the studied samples, which caused the local material structure transformation and the decrease in the elastic energy level. This improved the crack resistance under the cyclic mechanical loading. The effect of the accumulation of the rotational strain modes at the grain boundaries was discovered, which caused the local structure transformation at the boundary zones. In the fine-grained structure, the formation of grain conglomerates was observed, which increased the values of the specific modulus of the moment of force. This could be mutually compensated due to the small sizes of grains. At the same time, the coarse-grained structures were characterized by the presence of the small number of grains with a high level of the moments of forces at their boundaries. They could result in trans-crystalline cracking.