Tension Mode Research Articles

Magneto-viscoelastic rod model for hard-magnetic soft rods under 3D large deformation: Theory and numerical implementation

The main purpose of this work is to develop a three-dimensional (3D) viscoelastic rod model for hard-magnetic soft (HMS) rods under large deformation which are widely used active structures in soft robotics. To do so, the Simo’s viscoelasticity theory has been rationally incorporated into the geometrically exact 3D curved rod model. The proposed model includes the deformation modes of axial tension, shear, bending, and torsion, which is applicable to the HMS rods with arbitrarily initial curved and twisted geometries under 3D large deformation. The viscoelastic constitutive equations of the HMS rod in the present formulation are formulated, which include the general relaxation functions. To obtain the expression for the magnetic load, the rotation-based magnetic free energy density is introduced, and the governing equations of the HMS rod with magnetic load and body force are presented. To obtain the numerical implementation, an implicit time integration algorithm that simply extends the generalized-α method for the rotation group, and the corresponding variational formulation and its linearization of the rod model are derived. To validate the model, five numerical examples, including 2D dynamic buckling, 3D static, and 3D dynamic problem are presented. The dynamic problems include the dynamic snap-through behavior of a bistable HMS arch and damped oscillation of a quarter arc cantilever under 3D deformation. The simulation results show good agreement with the results reported in the literature.

Local heating at the running crack tip in bcc iron according to molecular dynamics

Abstract This study presents estimates of a possible temperature rise at the crack tip from three dimensional (3D) atomistic simulations of fracture via molecular dynamics (MD) technique. Simulations start from an initial temperature of 0 K. The pre-existing edge crack was loaded in tension mode I. Crack initiation in MD is accompanied by surface dislocation emissions and later by a cross slip of the emitted dislocations into other slip systems. This leads both to stress waves radiation and to local heating in the plastic zone created by these dislocations. The local heating at the crack tip in the surface layers reaches a level of 480–500 K at some atoms, but an average temperature in the plastic zone is lower and depends on a chosen crack tip zone size. In the bulk crystal, where no dislocation emission (i.e. no plastic zone) has been realized, no significant heating is observed at the crack tip. MD results at the free sample surface comply with experimental data for ferritic steels with a pre-existing notch, loaded (quasi-statically) in mode I, as well as with some continuum predictions.

A novel “S” chain structure mechanism model of magneto-rheological elastomer

Mechanism models based on chain-like structures are often used to characterize the morphology of magneto-rheological elastomer (MRE) and provide theoretical guidance for MRE preparation. However, widely used shear and tension mechanism models based on oblique straight chain or bent-chain structures have the limitation of insufficient accuracy in characterization, mainly because the internal particle chains of anisotropic MRE are not simple oblique straight or bent from scanning electron microscope (SEM) results. Therefore, the particle chain formation and particle interaction mechanism within MRE are revealed firstly. The theoretical results shows that particles tend to form S-like chain structures due to complex attraction and extrusion. On this basis, a novel “S” chain mechanism model is proposed, which is confirmed to have higher accuracy than the ideal shear model and tension model by comparing with the experimental results. The main reason is that the “S” chain mechanism model has realized the unification of shear, compressive, or tension mode, and integrates the fully coupled magnetic field, distribution parameters and interface stretching. The “S” chain mechanism model also takes into account the radius and volume fraction of the particles in MRE preparation, which makes it a more accurate guide to subsequent preparation.

Mechanical performance of liquid cold-poured interlayer adhesives in comparison to PVB, EVA, and ionomers

AbstractCurrently, liquid cold-poured adhesives are infrequently used as interlayers of laminated or laminated safety glass in structural glass applications, despite their inherent benefits. The potential advantages of these materials are characterized by easy handling, rapid curing devoid of elevated temperature or pressure requirements, and consequently, a comparatively low energy demand. Despite the prolonged availability of certain products in the market, comprehensive scientific inquiry into their mechanical and thermal material characteristics remains limited. In this paper, two specific liquid cold-poured interlayer adhesives are investigated for their mechanical material properties in an extensive test regime. To be able to classify the characteristic values of the adhesives within a correct framework, the materials currently holding the largest market share, including Polyvinyl Butyral (PVB), Ionomers, and Ethylene Vinyl Acetate (EVA), are also subjected to the experimental program. The temperature dependence of the material behavior is explored through Dynamic Mechanical Thermal Analysis (DMTA) experiments. Furthermore, the time-dependent material behavior at large deformations is scrutinized using various methodologies, such as tensile tests at different strain rates, cyclic tests, creep tests, and relaxation tests, all conducted in uniaxial tension mode. The outcomes of all tests led to promising results for one of the adhesives with advantages over those of PVB and EVA.

Viscoelastic and Birefringence Relaxation of Individualized Cellulose Nanofibers in the Dilute and Semidilute Regions.

Viscoelastic relaxation mechanisms of individualized cellulose nanofibers (iCNFs) dispersed in glycerol in the dilute and semidilute regions were investigated by linear viscoelastic and dynamic birefringence measurements. The birefringence relaxation of the iCNFs was described by the orientational and curvature modes of an existing viscoelastic theory for ideal semiflexible polymers (Shankar-Pasquali-Morse theory). However, the Shankar-Pasquali-Morse theory could not fully describe the iCNF viscoelastic relaxation at high frequencies. Considering the results for birefringence relaxation, the experimental tension mode of the iCNFs was evaluated to be higher than the theoretical value. These results show that the viscoelastic relaxations of the iCNFs are different from those of ideal semiflexible polymers, in contrast to cellulose nanocrystals (CNCs). As the iCNF concentration increased, the orientational mode dramatically slowed, which was more drastic than other semiflexible polymers, including CNCs. This anomalous behavior is likely due to the nonideal nature of iCNFs.

Investigation of notch position and fiber ratio on the fracture mode and energy of sfrc beam under the impact load

When the literature is examined, it is seen that a lot of study has been done on the crack propagation and fracture modes that occur under the influence of static loads in reinforced concrete (RC) structures. Studies in the literature show the effect of crack initiation, concrete compressive strength, and fiber volume fraction on the tension mode (Mode-I), shear mode (Mode-II), and mixed fracture mode that occurs in crack propagation under static load. However, the literature has not found a comprehensive study in which the fracture modes are examined under the effect of dynamic impact loading. For this reason, an experimental study has been planned in which hybrid steel fiber reinforced concrete (SFRC) notched beams with varying compressive strength will be tested under impact loading with a free-fall drop weight device designed by the authors. The experimental variables studied were determined as the change of the crack initiation point in the beams, the compressive strength of the concrete used to produce the beams, and the fiber volume fraction in the concrete mixture. The acceleration and impact load-time histories under the constant-energy-level impact loading applied to the beams were measured. Also, the crack shape, fracture mode, crack angle, and energy absorption capacities of the beams under impact load were interpreted. While the transition from Mode-I fracture form to Mode-II fracture form occurs under impact loading, the effects of concrete compressive strength and steel fiber ratio variables on energy absorption capacity, crack angle, and crack shape are studied. Increasing the distance of the notch from the beam midpoint in notched beams produced with concrete without fiber from 0 to 40, 80 and 120 mm caused the energy absorption capacity values to increase by an average of 39 %, 66 % and 86 %, respectively. Increasing the distance of the notch to the beam midpoint from 0 to 40, 80 and 120 mm in beams with 0.75 % and 1.5 % fiber ratio increased the energy absorption capacity values by an average of 40 %, 65 % and 86 %, respectively. In beams with 2.25 % fiber ratio, increasing the notch distance from 0 to 40, 80 and 120 mm increased the energy absorption capacity values by an average of 38 %, 62 % and 83 %, respectively.

Design methods and recommendations for flexural concrete beams reinforced with steel-fiber composite bars

This study aims to establish a complete theoretical model for the nominal flexural strength of concrete beams reinforced with steel-fiber composite bars (SFCB-RC), and determine an optimized range for the ratio of the diameter of the steel core to the diameter of SFCBs (η). Firstly, flexural failure modes for SFCB-RC beams were determined through theoretical analysis, and two failure modes including concrete crushing (compression failure) and FRP in SFCBs rupturing (tension failure) were recommended. It was confirmed that there exists a transition region between the failure modes of tension and compression, where both modes are possible. By conducting a statistical analysis of a database including 57 SFCB-RC beams, an upper-limit reinforcement ratio was recommended for SFCB-RC beams in the transition region. Simplified equations to predict the nominal flexural strength for compression-controlled SFCB-RC beams were proposed by directly using the constitutive model of SFCBs. The flexural strength equations for tension-controlled concrete beams reinforced with fiber reinforced polymer bars (FRP-RC) were confirmed to be also suitable for SFCB-RC beams. Validation of these equations was conducted using the assembled database. Furthermore, the parametric analysis revealed an optimal range of the ratio η (0.77–0.87). This suggested range can serve as a basis for standardizing the production specifications of SFCBs.

Graphene Oxide-Based Nanocomposites for Stereolithography (SLA) 3D Printing: Comprehensive Mechanical Characterization under Combined Loading Modes.

Additive manufacturing, particularly Stereolithography (SLA), has gained widespread attention thanks to its ability to produce intricate parts with high precision and customization capacity. Nevertheless, the inherent low mechanical properties of SLA-printed parts limit their use in high-value applications. One approach to enhance these properties involves the incorporation of nanomaterials, with graphene oxide (GO) being a widely studied option. However, the characterization of SLA-printed GO nanocomposites under various stress loadings remains underexplored in the literature, despite being essential for evaluating their mechanical performance in applications. This study aimed to address this gap by synthesizing GO and incorporating it into a commercial SLA resin at different concentrations (0.2, 0.5, and 1 wt.%). Printed specimens were subjected to pure tension, combined stresses, and pure shear stress modes for comprehensive mechanical characterization. Additionally, failure criteria were provided using the Drucker--Prager model.

M‐AGC tangent visco‐plastic operator with hardening/softening, and application to the visco‐plastic relaxation analysis of stable and unstable problems using fracture‐based geomechanical interfaces

AbstractA previous perfect visco‐plastic constitutive formulation of the Perzyna type incorporating the concepts of prescribed stress increments and m‐AGC tangent operator (m‐Assumed algorithmic generalized compliance tangent operator) is extended to the case of Hardening/Softening (H/S). This extension is possible thanks to the closed‐form solution developed for the evolution of the loading function during a visco‐plastic time step. The formulation is then applied to constitutive modeling of zero‐thickness interfaces on the basis of a well‐established fracture‐based elasto‐plastic formulation, which in this manner is extended to visco‐plasticity. The resulting model is implemented in the finite element (FE) and small‐strain context by using both a standard Newton Raphson scheme for physical visco‐plasticity in which visco‐plastic time corresponds to physical time, and a Visco‐Plastic Relaxation (VPR) scheme, in which time corresponds to a fictitious time governing the transition from the elastic to the inviscid elasto‐plastic response. The numerical implementation is verified satisfactorily for common loading cases at interfaces such as pure tension (mode I) opening and shear‐compression (mixed‐mode) cracking/sliding, showing that the visco‐plastic results match the predictions of the fracture mechanics inviscid model in the long term. In addition, it is also shown that the VPR strategy developed is capable of providing temporary stability while the equilibrium path is recovered during instability events such as a snap‐back in the load‐displacement curve. This feature opens the door to a number of potential advanced applications of the formulation developed in the geomechanical context.

Manufacturing process and annealing influence on the dynamic mechanical properties and physical structure of LLDPE thin films

Thin films of Linear Low-Density Polyethylene are used for stratospheric balloon applications. They undergo tensile mechanical stress on a wide range of temperatures [-95; 55]°C. The aim of this study is to compare the influence of blown film and double-bubble manufacturing processes on the crystalline phase and mechanical properties of the films through their operating temperatures (flight, storage, and transportation temperatures). Dynamic Mechanical Analysis and Differential Scanning Calorimetry have been used to monitor the dynamic mechanical properties in tension mode and the crystalline phase of the films respectively. The films mechanical properties are dependent on their manufacturing process. The double-bubble process allows isotropic tensile mechanical properties regarding stretching direction, whereas the blown film process favors only transversal direction. To simulate different storage conditions, annealing has been performed. The influence of annealing on the tensile mechanical properties of the films depends mainly on the internal stress stored during manufacturing. The double-bubble process produces a biaxially stretched film with a higher stretching ratio than blown films. The dissipated internal stress can be associated with thermal shrinkage and goes up to 10 % for the biaxially stretched film. The more internal stress is stored, the more E′ and E″ increases. Annealing also favors the formation of a secondary crystalline phase that is dependent on annealing temperature and time, and exhibits αc relaxation. After annealing, the amorphous phase is less stretched, and the crystalline phase keeps its orientation.

Improving energy absorption and failure characteristic of additively manufactured lattice structures using hollow and curving techniques

Strut-based lattice structures of various types exhibited a common critical issue, namely, high tensile stress concentration occurred at node-to-strut sites, which often led to lowered energy absorbability as compared to triply periodic minimal surfaces structures. Therefore, this work aimed for improving the Octet-truss structure by a combined technique using hollow core and varying cross-section ratio. Firstly, test specimens were fabricated using a stereo-lithography based additive manufacturing of photopolymer hard resin. Elastic-plastic properties and damage criterion of the used polymer were experimentally determined and applied for finite element models. Validation by compressive tests of lattice samples showed deviations of stress–strain responses less than 12%, in which local deformation and subsequent damages were fairly predicted. Afterwards, finite element simulations of designed lattice structures subjected to compressive, combined shear, shear and tensile loads were performed and obtained stress–strain characteristics including total absorbed energies and deformation behaviors were studied. Under uniaxial compression and combined shear loads, modified Octet-truss structures exhibited considerable increases of energy absorptions up to 173% and 116%, respectively, and stress–strain responses were more stable. On the other hand, by tension mode peak stresses and elongations could be enhanced about 41% and 11%, accordingly. The improved performances of proposed strut-based structures were comparable to those of triply periodic minimal surfaces diamond structure. This was due to that local stress distributions in the structure became more uniform and previously dominated tensile stresses were switched to compressive stresses. Therefore, occurrences of shear bands and plastic hinges could be effectively inhibited.

Sustainable Polypropylene-Based Composites with Agro-Waste Fillers: Thermal, Morphological, Mechanical Properties and Dimensional Stability.

Natural fiber composites (NFC) are eco-friendly alternatives to synthetic polymers. However, some intrinsic natural fillers' properties hinder their widespread implementation as reinforcement in polymeric matrices and require further investigation. In the scope of this study, the thermal, rheologic, mechanical (tension and flexural modes), and morphological properties, as well as the water absorption and dimensional stability of the NF polypropylene (PP)-based injection molded composites reinforced with rice husk (rh) and olive pits (op) of 20 wt.% and 30% wt.%, respectively, were investigated. The results suggest that the higher content of the rice husk and olive pits led to a similar reduction in the melt flow index (MFI), independent of the additive type compared to virgin polypropylene (PPv). The melting and crystallization temperatures of the PPrh and PPop composites did not change with statistical significance. The composites are stiffer than the PP matrix by up to 49% and possess higher mechanical strength in the tension mode at the expense of decreased ductility. PPrh and PPop have a superior flexural modulus in the bending mode, while the flexural strength improvement was accomplished for the PP30%rh. The influence of the fibers' distribution in the bulk of the parts on their mechanical performance was confirmed based on a non-localized morphology evaluation, which constitutes a novelty of the presented research. The dimensional stability of the composites was improved as the linear shrinkage in the flow direction was decreased by 49% for PPrh and 30% for PPop, positively correlating with an increase in the filler content and stiffness. PPop was less susceptible to water sorption than PPrh due to fibers' composition and larger surface-to-area volume ratios.

Experimental Study and Seismic Response Evaluation of Chlorobutyl Rubber-Based Viscoelastic Dampers

Conventional viscoelastic devices often use high-damping elastomeric pads, typically made of patented formulations, that are bonded to steel plates. The response properties of these pads under cyclic shear deformations directly influence the load-deformation hysteretic response of the device. Chlorobutyl (CIIR) is a high-damping rubber commonly used in industrial applications. However, this study found that the damping properties of a typical CIIR rubber compound are insufficient for effective structural seismic mitigation at ambient temperatures above 0°C. The goal of this study was to develop a new composite of CIIR, referred to as modified CIIR, with improved damping properties and to compare its performance with that of the reference CIIR rubber. In the first phase of the experimental studies, the viscoelastic characteristics of the reference and modified CIIR rubber materials were evaluated using dynamic mechanical thermal analysis (DMTA) in tension mode. Prototype viscoelastic damper devices were then fabricated from both the reference and modified CIIR rubber materials and subjected to cyclic shear tests at room temperature and various loading frequencies. The results showed that the modified CIIR rubber exhibited significantly improved effective damping compared to the reference CIIR. The final component of this study involved investigating the seismic response of a 2D frame structure equipped with prototype dampers made from both reference and modified CIIR materials, using nonlinear time-history analyses. The analysis results indicated that the modified CIIR rubber can be effectively utilized in the seismic response mitigation of structures.

Prediction of contact pressure during cold rolling of thin strips with predominance of front tension

The results of theoretical studies of the average relative contact stress during cold rolling of thin steel strips with a predominance of front tension are presented. The transition from symmetric to the asymmetric tension mode helps to reduce the contact stress by 6.4...13.5 %. This makes it possible to increase the service life of rolling rolls. A regression equation is obtained for predicting of the average relative contact stress for the studied range of change in the main technological parameters.

Study on Failure Energy per Unit Area of Concrete Specimens Based on Minimum Energy Dissipation Theory.

In order to study the strength change of concrete specimens under different loading conditions, based on the principle of minimum energy dissipation, the damage energy per unit area of concrete was studied. By using finite element numerical simulation software for concrete specimens with different failure modes of tension, pressure, bending and torsion, a double-broken line damage constitutive model is adopted. The failure forms of concrete specimens under different loading conditions, as well as the failure area and failure energy of each specimen during loading, are simulated and analyzed. The failure energy per unit area under different failure modes was quantitively calculated, the relationship between the failure area and failure energy consumption under different failure modes was analyzed. The results show that, under different failure modes, the failure area of concrete specimens is different, the energy consumed during failure is different, and the strength is different. However, no matter how the failure mode changes during the failure process, the failure energy W per unit area remains constant and fluctuates in the range of 2.0~6.0 mJ/cm2, which is related to the physical properties of concrete itself.

Energy absorption capacity under tensile and compressive loads of auxetic metamaterial structures

An auxetic metamaterial is a mechanical metamaterial with a negative Poisson’s ratio. When compressed or stretched in one direction, it contracts or expands in a perpendicular direction. This review paper focuses on the energy absorption of auxetic metamaterial structures and their applications. Starting with the original structure proposed by D. Han et al., another structural model with heuristically enhanced ribs is proposed to suit the structure’s anisotropy, reduce mass, and increase energy absorption. An extension to this is the newly designed MH-1 model, which is lightweight compared to commonly reported auxetic forms. Numerical results show that MH-1 has the best specific energy absorption and exhibits an obvious auxetic effect under tension, with symmetrical and stable deformation modes. Auxetic metamaterials are also progressively finding applications in the biomedical field. One of the most promising applications of auxetic is in the development of new and improved prosthetics and implants.

Dynamic Axisymmetric Tension of a Thin Round Ideally Rigid-Plastic Layer

We consider the stress-strain state that occurs during dynamic tension of a homogeneous round layer of an incompressible ideally rigid-plastic material that obeys the Mises–Genka criterion. The upper and lower bases are stress-free, and the radial velocity is set on the lateral boundary. The possibility of thickening or thinning of the layer is taken into account, which simulates neck formation and further development of the neck. Two characteristic tension modes are revealed. First one is associated with a rather high rate of removal of the side boundary of the layer from the center, the second one is associated with acceleration. In the second case, we have carried out an analysis using the method of asymptotic integration, which makes it possible to approximately find the parameters of the stress-strain state.

Quantification of inhomogeneity and anisotropy of bituminous mixtures using biaxial experimental data

Most of the existing mechanical characterization test methods and the analytical models for bituminous mixtures are developed based on the assumption of homogenous and isotropic material properties. However, the extent to which such assumptions hold good for bituminous mixtures is not very clear. A biaxial testing scheme in indirect tension mode can come in handy to collect the experimental data at different test temperature regimes. In this study, a bituminous mixture with a nominal maximum aggregate size (NMAS) of 13.2 mm is used to fabricate cylindrical test specimens with 150 mm diameter and 63.5 mm thickness for conducting the repeated load indirect tension (IDT) test. The input load level is selected as 5 to 13 % of the indirect tensile (ITS) failure load in the form of a haversine pulse of 0.1 s loading and 0.9 s rest period. Such loading is applied on zero-degree and ninety-degree orientations of the specimen. The resulting deformations in different directions are measured using linear variable differential transducers (LVDT) attached to both diametral faces of the specimen. The response of the bituminous mixture specimen is captured at three different temperatures of 20, 25, and 30 °C using two different gauge length (half and quarter gauge of the total diameter). A new framework is introduced in this study to evaluate the extent of inhomogeneity and anisotropy of bituminous mixtures. The deformation response of the test specimen captured in the same orientation at different diametral faces is compared to evaluate the extent of inhomogeneity. The extent of anisotropy is evaluated by comparing the deformation response of the test specimen captured at different orientations within the same diametral face. A 15 % variation in the average peak deformation is chosen as the demarcation for determining the extent of inhomogeneity and anisotropy. From this investigation, it is observed that half gauge length experimental data exhibits homogenous and isotropic behavior for all three test temperatures. The quarter gauge length data exhibit similar behavior at 30 °C, whereas it is observed as homogenous and anisotropic at the other two test temperatures.

A transverse failure criterion for unidirectional composites based on the Puck failure surface theory

Puck criterion, a transverse failure criterion for composites, has more applications in engineering, but the empirical nature of its mathematical expression and the complexity of its parameters hinder its further development. In this work, a failure function is proposed based on the Puck hypothesis. According to the parameters of composites in special states, two modes of transverse tension and compression are distinguished, the pending coefficients in the failure function are derived, and then a transverse failure criterion for composites is formulated. The proposed criterion was evaluated experimentally in terms of envelope curves and off-axis strength using the existing data in the literature, and was compared with several other criteria. The results show that the proposed criterion is in good agreement with the experimental data, and its prediction accuracy ranks high among several criteria, demonstrating the rationality of the proposed criterion. Additionally, the effect of material parameters on the proposed criterion is analyzed and the results show that changes in transverse tensile and compressive strength can change the strengthening effect of transverse compression against in-plane shear, while changes in in-plane shear strength cannot change the strengthening effect. This work provides a correction method for the Puck criterion, which has a more rational mathematical expression with fewer parameters and can be used in the design of engineering composite structures, which has significant design reference value and theoretical significance.

Microstructural Control by Cooling Rate in β-type and Sintered Ti-3.6Fe-5Zr-0.2B (Mass%) Alloy Fabricated by Spark Plasma Sintering and Heat Treatment

The β-type and sintered Ti-3.6Fe-5Zr-0.2B (mass%) alloy has been consolidated by spark plasma sintering, followed by a β solution treatment (ST). In order to obtain a high-strength ductile balance, water quenching or air cooling is used after ST. Modification of sintering conditions, which leads to 100% of the relative density, improves the tensile ductility. The Fe addition causes a large local lattice and compressive strain to the bcc Ti lattice; in the water-quenched sample, α” martensite phases appear in the β matrix. When air cooling is applied after the ST, bimodal α lath phases are instead precipitated during the cooling in nanoscale, and the formation of α” martensite phases is suppressed. This results in high strength and better ductility when compared with those in the water-quenched sample, particularly in tensile properties. The air-cooled sample reveals attractive mechanical properties in both tension and compression modes.