Quasi-static Loading Research Articles

Quasi-static crushing response of a novel triaxial isotropy mechanical metamaterial with dual-platform property

A novel triaxial isotropy origami metamaterial with dual-platform is proposed by combining the tachi tubes and the honeycomb structures. Crushing responses of the hexahedral metamaterial under quasi-static compression load are investigated through experimental tests and numerical simulations. Experimental and numerical results reveal that the hexahedral metamaterial sample shows three deformation modes. Meanwhile, the numerical predictions of deformation modes and locations agree very well with the experimental results. Moreover, the effect of aspect ratio, thickness-to-span ratio, angle on the deformation mode, peak stress, plateau stress of different stages, and specific energy absorption (SEAM, SEAV) is investigated. Finally, the proposed metamaterial is compared with traditional honeycomb. The numerical results demonstrate that the SEAM of the hexahedral metamaterial is 90.6% of the traditional honeycomb in the Z-direction. However, during X/Y-direction compression, the energy absorption capacity of the hexahedral metamaterial is 13.0 and 12.2 times that of the traditional honeycomb, respectively.

Peridynamics model of torsion-warping: Application to lattice beam structures

This paper presents a finite deformation beam model based on Simo-Reissner theory in peridynamics (PD) framework to deal with torsion induced warping deformation. Seven degrees of freedom, viz. three translational, three rotational, and one warping amplitude are considered at each material point. The governing equations of the beam are obtained by employing global balance of linear and angular momenta in conjunction with Simo's assumption on the deformation field. The relation between PD resultant force, moment, bi-moment, and bi-shear states with their classical counterparts is established using the constitutive correspondence method. Numerical implementation strategy is furnished for both quasi-static and dynamic cases. The solution for quasi-static load is obtained through the Newton-Raphson method. The proposed model is validated against finite element solutions considering cantilever beam and lattice structures. Quasi-static deformation responses of 3×3×3 octet and single unit compression-torsion lattice structures are presented further to demonstrate the effectiveness of proposed beam model. A new bond breaking criterion is proposed based on critical stretch, critical relative rotation, and critical relative warping amplitude and failure of the compression-torsion lattice structures under compressive load is simulated. The Newmark-beta method is utilized to solve the governing equations for dynamic loading. Numerical simulations include dynamic analysis of octet and compression-torsion lattice structures.

Improving dynamic energy absorption performance and stability loss prediction of an all-PET sandwich structure through artificial neural networks

Abstract One key characteristic that is frequently studied in composite sandwich structure mechanics is low-velocity impact performance. Single polymer composites present higher ductility when compared to traditional glass fibre and carbon fibre reinforced plastic composites (GFRP, CFRP), which makes them strong candidates for impact energy absorption. These lightweight structures are also fully recyclable due to their all-PET constituents, an important aspect when considering possible applications. In this paper an existing second order composite SrPET and PET foam sandwich structure (self-reinforced poly-ethylene terephthalate matrix and fibre) is numerically investigated for optimal structural design configuration under out-ofplane, low velocity, dynamic loading. The study explores the parametric geometry interdependencies of the structure’s configuration with respect to its energy absorption potential. The results are then compared to the quasi-static loading performance behaviour studied by M.N. Velea et all [1]. This work provides a deeper understanding of how geometry configurations can influence energy absorption capabilities highlighting structural strengths and weaknesses while exploring non-equilateral triangle configurations. The Design Space Exploration (DSE) is carried out by using an optimization algorithm for a dynamic out of plane 3D impact simulation based on the finite element (FE) method software. The synergy between DSE and FE generates a guided simulation loop that can successfully be used to train a neural network to predict the dynamic behaviour of different geometric configurations from the exploration space. Based on the data samples obtained, an artificial neural network (ANN) is built to predict the energy absorption capacity for a given set of structural design parameters, useful in experimental validation test cases.

LOADS ON SUBMERGED WALLS OF PROTECTIVE STRUCTURES

The intensification of military operations on the territory of Ukraine, which are accompanied by missile attacks and bombing of territories, requires the use of reliable protective structures. Modern codes require the provision of each new building with storage facilities that guarantee the safety of life and health of citizens, so the correct determination of all loads on the structural elements of protective structures is an urgent issue. Taking into acoount the fact that the previous codes were somewhat outdated and had limited access for a long time, a significant event was the adoption in 2023 of new codes for the design of protective structures of civil defence. The main requirements and recommendations of SBC B.2.2-5:20023 were taken into account when conducting research on determining the loads on buried walls of bomb shelters. Such structures, as we know, perceive a constant load from the lateral pressure of the soil, which during an explosion is supplemented by an episodic load from the action of an air wave. Modern specialized literature contains rather limited information on scientific research and development in the field of design of protective structures. An actual issue is also the study of the influence of determining factors on the intensity of the load on the walls of buried protective structures and the possibility of its adjustment in order to reduce it. Taking into account the nature of the distribution of loads on the underground walls of bomb shelters, a dependence was obtained to determine the resulting active pressure and quasi-static load caused by the action of an air wave. The pressures from the soil and the blast wave at different orientations of the contact wall and for different types of soil environment were studied. The loads in contact of a smooth and rough wall with sandy, sandy and loamy soils with different indicators of physical and mechanical characteristics were considered. The obtained results indicate a significant influence of the geometric parameters of the wall and the features of the contact soil on the resulting pressure, which can vary depending on the studied factors by 10-20%, which indicates the possibility of reducing the load on protective structures, operating with the considered indicators.

Technological and Mechanical Studies on Additively Manufactured Cellular Structures Made of the Ultrafuse 316L Composite Filament

Regular cellular materials produced using additive manufacturing (AM) techniques represent a significant development trend in modern engineering materials. Depending on the applied elementary unit cell of topology, it is possible to define the course of the structure deformation process in order to obtain the highest possible energy absorption effectiveness. This feature makes regular cellular structural materials particularly attractive for a number of industrial branches. This paper presents the results of technological trials and the results of experimental studies on the mechanical properties of regular cellular structures made using 3D printing technology under compression test loading conditions. The material used for their production was the Ultrafuse 316L filament and the fused filament fabrication (FFF) technique. The proposed material is a polymer-metal composite with a manufacturing process similar to metal injection moulding (MIM). The adopted research methodology included a feasibility study aimed at achieving material homogeneity and compression tests of the developed and manufactured regular cellular structures under quasi-static loading conditions. Several structural topologies were analysed. Experimental results indicated that regular cellular structures made from 316L steel exhibit high mechanical strength and extensive plastic deformation capabilities. The utilized in this work manufacturing technology used combines the advantages of 3D printing process with the potential of powder metallurgy. The proposed technique of structure manufacturing process is much cheaper than other based on melting metallic powders.

Penetrative fracture behavior of monolayer graphene oxide: nanoscale experiment and molecular dynamics simulation

Abstract Graphene, a two-dimensional material, is expected to be employed as a next-generation component for structural and functional applications because of its light weight and excellent mechanical properties. For applications requiring lightness and impact resistance, preventing penetrative damage upon particle impact is critical for applications in mechanical protection. However, graphene is known to have high defect sensitivity. Graphene oxide (GO) may be a better candidate, as functional groups (e.g., hydroxy and epoxy groups) bonded to the C–C network in GO result in better deformability, ductility, and durability compared to graphene. For mechanical applications, it is crucial to understand the fracture behavior, especially the penetrative fracture behavior, of GO membranes. This study characterizes the penetration behavior and fracture morphology of GO membranes subjected to particle impact. Nanoscale experiments were conducted using an atomic force microscope and laser-induced particle impact test for GO. These material testing methods employ nanoscale spheres to induce particle penetration, with the former experiment conducted under quasi-static loading and the latter under dynamic loading. Additionally, molecular dynamics simulations were performed to elucidate the fracture mechanisms of GO. Finally, cyclic fatigue experiments and simulations revealed that GO’s ductility provides resistance to catastrophic failure, indicating its durability. These comprehensive investigations provide valuable insights into the fracture properties of GO membranes under impact penetration.

Experimental characterization of aluminum/polymer/aluminum sandwich structures under various loading rates and temperatures: Establishing a constitutive relationship for LDPE

Composite sandwich structures, for example Alucobond, have appeared as auspicious materials in a diversity of engineering applications due to their lightweight, high strength to weight ratio and thermal insulation properties. Analyzing their mechanical behavior in different loading rates is critical to optimizing their performance. This study inspects the mechanical response of Alucobond sandwich composite structures under dynamic and quasi-static compression loadings. Dynamic compression tests, carried out at high strain rates, and quasi-static compression tests, carried out at lower strain rates and temperatures, were used to predict the behavior of the material under different loading conditions. In addition, the mechanical properties of the low-density polyethylene (LDPE) core layer were characterized under dynamic and quasi-static loading conditions, with varying strain rates and temperatures, leading to the establishment of a constitutive relationship for the LDPE material. The comparative study of Alucobond and LDPE highlights the influence of material composition and loading conditions on the mechanical behavior of the composite sandwich structures.

Energy absorption structure with negative stepped plateau force characteristics under quasi-static loads

The force-displacement curve is the key to determine the energy absorption performance. Customizing the force-displacement curve enables the design of more advanced and efficient energy absorption systems. In this paper, we introduce a negative stepped plateau force structure (NSPFS) design by combining crooked plate units with curved and straight combined cross-section (CSCC) units. First, the NSPFS is fabricated by using additive manufacturing technology, and a compression experiment is conducted to validate the design methodology. Then, a finite element model is developed and compared with the experimental results to verify its effectiveness. The peak force (PF) and mean crushing force (MCF) of the crooked plate unit are primarily controlled by wall thickness t1 and initial angle θ1. When θ1 = 1.146° and t1 = 1.0 mm of crooked plate unit, the lowest point of the plateau phase decreases by 84 % compared to the PF, and the ratio of PF to MCF is 4.9. When the PF of the crooked plate unit is greater than the PF of the CSCC unit, the structure has the characteristics of negative stepped plateau force. More phase plateau forces can be obtained when multiple NSPFS are compressed in series. When multiple NSPFS units are compressed in parallel, multi-phase continuous negative stepped plateau force can be achieved. Therefore, NSPFS allows for the customization of complex force-displacement curves through series and parallel design.

Seismic damage assessment of bonded versus unbonded laminated rubber bearings: A deep learning perspective

Laminated Rubber Bearings (LRBs), widely employed in highway bridges worldwide, are vulnerable to shear failure, squeezing or displacing during seismic events, potentially compromising bridge safety. Establishing a reliable approach for assessing the damage of LRBs is crucial for evaluating the seismic performance of bridges and preventing serious damage. To address this concern, this paper proposes a novel approach for LRBs seismic damage assessment based on computer vision (CV) technique. First, quasi-static loading tests are conducted on both bonded and unbonded LRBs to effectively enhance the understanding of their nonlinear properties. Subsequently, a large number of bearing samples are investigated to develop a comprehensive image database for a CV-based damage assessment model. A deep convolutional network (CNN) is designed to segment damage pixels, which are then combined with damage indicators to quantify the impact of various influencing factors on seismic damage using the interpretable machine learning technique, Shapley value. The results demonstrate that the CNN model achieves high-precision pixel segmentation and accurate predictions of seismic damage to LRBs, with RMSE consistently below 0.009 and R2 exceeding 95 %. The primary factor influencing LRB damage is the type of constraint, which interacts with loading characteristics and geometric dimensions to produce various coupled effects. This high-precision CV-based approach shows significant potential for estimating seismic damage states of critical bridge components and building seismic protection.

Fragility functions for structural-architectural shear walls with interlocking modules

ABSTRACT Tessellated structural-architectural (TeSA) shear walls, consisting of interlocking tiles, enable repairability because of modularization, and can satisfy both structural and architectural demands. This paper characterizes the behavior of TeSA walls made of 1-D interlocking reinforced concrete tiles using fragility functions. Two TeSA walls with varying tile patterns are analyzed under lateral loading. The modeling approach is validated using test results under quasi-static cyclic lateral loading. Damage states at tile and wall levels are defined, and a framework for generating fragility functions for TeSA walls is proposed considering uncertainties in the applied axial loading, tile-interface properties, modeling approach, and material properties of concrete. The results show that TeSA wall fragility functions are sensitive to tile shapes and patterns, particularly for the severe damage state. The onset of moderate and severe damage for TeSA walls is at 1% and beyond 2% drift ratios, respectively, showing high resistance of TeSA walls to damage.

New 3D petal-like structures with lightweight, high strength, high energy absorption, and auxetic characteristics

A novel type of petal-like structure that exhibits superior mechanical properties, was proposed and fabricated by integrating advantages of metamaterial, multi-stage deformation, and high strength of fiber-reinforced composites. Compression testing and finite element analysis were first conducted on three petal-like structures formed with different angles and made from fiber-reinforced composites. The findings indicated that these composite-based multi-cell structures can also exhibit a satisfactory stress plateau stage through judicious structural design. After ensuring the structures' performance under quasi-static compression load, the impact resistance of the new structures was further examined. It was found that the structure's auxetic characteristics diminished under low-speed impact load. However, under a 20 J impact load, the structures exhibited energy absorption characteristics (SEA) that surpassed those of both conventional and other new auxetic structures by 8–40 times. These promising results demonstrate that the newly designed petal-like structures have high potential applications in various fields such as construction and automotive industries.

Modeling of residual stiffness phenomenon in modified Iwan model of bolted joints and its application

Bolted joints have been widely used in various mechanical structures. Due to the presence of contact interfaces, the joints exhibit complex nonlinear behavior under dynamic loading. Effective prediction of the dynamic response of bolted structures requires the construction of appropriate dynamic models. This paper proposes a modified Iwan model which gives a more comprehensive description of joints than the previous Iwan models, especially for the phenomenon of residual stiffness in macro slip. The equations of the model's backbone curve, hysteresis curve, and energy dissipation are derived. The parameter identification procedure is also provided. Subsequently, connection elements based on the modified Iwan model are integrated into a single bolted joint and a thin-walled cylinder containing multiple bolted joints, the responses under quasi-static unidirectional loading, quasi-static cyclic loading and constant-frequency excitation are investigated. The physical interpretation of the parameters in the model is discussed, thus explaining the relationship between the bolted joint's physical parameters and some important variables. The results indicate that the model can effectively characterize the nonlinear mechanical behavior of the bolted joint for both micro and macro slip regime, with significant improvement in computational efficiency.

Investigations on the finite strain behavior of standard PVB: experiment and modeling

AbstractThe numerical simulation of the residual load-bearing capacity of laminated glass is one of the most relevant topics of current research in structural glass engineering. The mechanical description of the behavior of the interlayer plays a crucial role. Several approaches and models already exist in automotive engineering and structural protection. Structural glass design assuming quasi-static loads misses a detailed model so far. The aim of this work is the mechanical description of the time-dependent behavior of Polyvinylbutyral (PVB) under large deformations considering quasi-static loading. The results of experiments on single-layer Standard PVB are presented, and a model of finite nonlinear viscoelasticity is derived. In particular, the formulation of phenomenologically motivated viscosity functions is described. Subsequently, the model parameters are calibrated on the experimental results, and the uniaxial stress state is simulated.

Quantification of delamination resistance data of FRP composites and its limits

Quantitative delamination resistance data of fibre-reinforced polymer-matrix (FRP) composites for quasi-static or cyclic fatigue loads are determined under different loading modes and load rates, respectively. Such data find use, e.g., in FRP materials’ development, materials’ selection, assessment of durability, or structural design. Round robins during test development yielded repeatability and reproducibility (coefficients of variation) of roughly 10 to 25%. This scatter has several different sources. Intrinsic material variability amounts to a few percent at best, at least for advanced manufacturing processes. This intrinsic scatter is essential for material comparisons and structural design. Measurement resolution specified in standardised test procedures yields a maximum of 4–5% variability. Most of the remaining scatter comes from other, extrinsic sources. Test operator actions, e.g., choice of test set-up, manual data acquisition or data analysis can yield extrinsic scatter. Damage mechanisms during delamination initiation and propagation act on the micro- and meso-scale, typically a few micrometer to a few hundred micrometer in size, with corresponding time-scales estimated to between a few tens of nanoseconds and a few microseconds. Defect size-scales are hence several orders of magnitudes lower than test specimen and structural scales, respectively. Predictive capability of models using such test data for structures are, therefore, limited. Major issues are up-scaling from straight beam-like specimens to larger shell-like structures, possibly with complex shape and varying thickness as well as from unidirectional fibre orientation to multidirectional lay-ups.

The Quasistatic Pressure Characteristics of a Confined Cabin in a Water Mist Environment

To investigate the quasistatic pressure load characteristics of an explosion in a confined cabin in a water mist environment, explosion tests were conducted under different explosive and water mist masses. The concentration of water mist, droplet diameter, and quasistatic pressure inside the cabin were measured. On the basis of the theoretical model of quasistatic pressure in adiabatic ideal gas cabins, a theoretical model of the quasistatic pressure in a confined cabin in a water mist environment was established. On the basis of experimental data and theoretical models, an empirical formula was proposed for the peak quasistatic pressure of implosion in a water mist environment. A model for a cabin explosion in a water mist environment was established, and the load characteristics of a cabin explosion under high water mist concentrations were analyzed. The relevant research results contribute to the prediction of the quasistatic pressure of explosions in a confined cabin in a water mist environment.

Close-in explosion performances and damage evaluation of bamboo fiber reinforced laminates

Three types of laminated bamboo plates (LBPs), namely flat-pressed one-way plate (PR), flat-pressed orthogonal plate (PC), and side-pressed one-way plate (PT), were designed and manufactured to investigate their mechanical responses under quasi-static and blast loadings. The experimental results show that the LBPs have excellent blast resistance. In-field explosion experiments clearly reveal the damage patterns of the LBPs with scaled distance changing from 2.052 m/kg1/3 to 0.054 m/kg1/3. Plates PR and PT have five damage patterns, which are slightly scorched, matrix cracking, fiber breakage, spalling and outbreak-crash, respectively. Plates PC eliminate the matrix cracking damage pattern through balancing the anisotropy by orthogonal structure. After explosion, the LBPs still maintain good elasticity, structural integrity and high residual bearing capacity. The residual bearing capacity of plates PR-1, PT-1 and PC-1 repetitively suffered seven explosions is decreased to 58.8 %, 42.6 % and 68.7 % of the average bearing capacity of the reference plates, respectively. It is concluded that orthogonal and side-pressed structures are conducive to enhance the load carrying capacity of the LBP.

Energy absorption of thin-walled multi-cell tubes with DNA-inspired helical ribs under quasi-static axial loading

Energy absorption of thin-walled multi-cell tubes with DNA-inspired helical ribs under quasi-static axial loading

Experimental investigation and numerical modelling of the seismic performance of reinforced concrete - engineered cementitious composite short columns

Four reinforced concrete - engineered cementitious composite (RC-ECC) short columns and one RC short column were subjected to quasi-static loading testing in this study. Digital image correlation (DIC) technology was adopted to observe the loading process. Thereby the influence of ECC replacement height and axial compression ratio on the seismic behavior of RC-ECC short columns was systematically studied. The test results indicate that all specimens had undergone flexural-shear failure dominated by shear failure. As the replacement height of ECC added, the number of horizontal cracks in the specimen enlarged, whereas the number and width of oblique cracks progressively diminished; The specimen's bearing ability changed less, the deformability and energy dissipation ability improved, and the shear strain and the proportion of shear deformation constantly dropped. Nevertheless, with the rising of ECC replacement height in a certain range, the improvement in seismic performance of the column decreased. As the axial compression ratio improved, the number of oblique cracks in the specimen reduced, the width of the main shear oblique crack enlarged, and the deformation capacity, energy dissipation capacity, and shear deformation proportion all exhibited a downward trend. Finally, based on the ABAQUS finite element platform, a numerical model of RC-ECC short columns was established and confirmed.

Biomechanics on Ultra-Sensitivity of Venus Flytrap's Micronewton Trigger Hairs.

Numerous plants evolve ingeniously microcantilever-based hairs to ultra-sensitively detect out-of-plane quasi-static tactile loads, providing a natural blueprint for upgrading the industrial static mode microcantilever sensors, but how do the biological sensory hairs work mechanically? Here, the action potential-producing trigger hairs of carnivorous Venus flytraps (Dionaea muscipula) are investigated in detail from biomechanical perspective. Under tiny mechanical stimulation, the deformable trigger hair, composed of distal stiff lever and proximal flexible podium, will lead to rapid trap closure and prey capture. The multiple features determining the sensitivity such as conical morphology, multi-scale functional structures, kidney-shaped sensory cells, and combined deformation under tiny mechanical stimulation are comprehensively researched. Based on materials mechanics, finite element simulation, and bio-inspired original artificial sensors, it is verified that the omnidirectional ultra-sensitivity of trigger hair is attributed to the stiff-flexible coupling of material, the double stress concentration, the circular distribution of sensory cells, and the positive local buckling. Also, the balance strategy of slender hair between sensitivity and structural stability (i.e., avoiding disastrous collapse) is detailed revealed. The unique basic biomechanical mechanism underlying trigger hairs is essential for significantly enhancing the performance of the traditional industrial static mode microcantilever sensors, and ensure the stability of arbitrary load perception.

Bidirectionally graded honeycombs under quasi-static loading: Experimental and numerical study

Density-graded cellular solids possess tailorable mechanical properties through variable localized densities, made possible with design freedom offered by additive manufacturing. In this paper, a novel design strategy is proposed to generate bidirectionally graded honeycombs where the gradient direction is both parallel and perpendicular to the loading direction. A gradient function is developed to design three density gradient honeycombs having three different thickness gradients. The graded honeycombs along with their uniform density regular honeycomb counterparts of similar relative density are manufactured using material extrusion process. In-plane compression tests are carried out to perform a comparative study of the honeycombs. Unlike the regular honeycombs, graded honeycombs show layer-by-layer deformation, in addition to cell-wise collapse in lateral direction. Graded honeycombs show better energy absorption characteristics in low and high energy compressions, and high strain regime. Also, graded honeycombs have similar or higher specific energy absorption, densification strain, mean crushing force, and peak crushing force. The compressive responses of the honeycombs are simulated with finite element analysis and the simulation results agree well with the experimental results. The results substantiate the significance of thickness gradient in controlling the density gradation, and effectively tailoring the load-bearing capacity, deformation behavior, and energy absorption characteristics of cellular structures.