Time-dependent Stress Relaxation Research Articles

Experimental study on the mechanical properties of the reinforced transparent building membrane material STFE

STFE is a new type of reinforced polymer building membrane material that combines excellent mechanical properties and transparency by using high-strength fibre mesh, which eliminates the limitations of poor transparency in coated fabric membranes and low strength in polymer membranes. In this study, in order to investigate its strength indicators and mechanical properties, material mechanical tests such as uniaxial, biaxial, and picture frame tests were conducted, obtaining the basic mechanical parameters of the material, including warp and weft direction tensile strength, tear strength, welding seam strength, elastic modulus and Poisson's ratio, shear modulus, and creep elongation rate, among others. Additionally, linear and nonlinear stress–strain mechanical models for uniaxial and biaxial loading were proposed for this material, as well as time-dependent creep and stress relaxation models. These mechanical models were validated and found suitable for numerical simulations of the material. The research results lay the preliminary foundation for the application of this material in large-span tensile transparent membrane structures.

Remolding and Deconstruction of Industrial Thermosets via Carboxylic Acid-Catalyzed Bifunctional Silyl Ether Exchange

Convenient strategies for the deconstruction and reprocessing of thermosets could improve the circularity of these materials, but most approaches developed to date do not involve established, high-performance engineering materials. Here, we show that bifunctional silyl ether, i.e., R'O-SiR2-OR'', (BSE)-based comonomers generate covalent adaptable network analogues of the industrial thermoset polydicyclopentadiene (pDCPD) through a novel BSE exchange process facilitated by the low-cost food-safe catalyst octanoic acid. Experimental studies and density functional theory calculations suggest an exchange mechanism involving silyl ester intermediates with formation rates that strongly depend on the Si-R2 substituents. As a result, pDCPD thermosets manufactured with BSE comonomers display temperature- and time-dependent stress relaxation as a function of their substituents. Moreover, bulk remolding of pDCPD thermosets is enabled for the first time. Altogether, this work presents a new approach toward the installation of exchangeable bonds into commercial thermosets and establishes acid-catalyzed BSE exchange as a versatile addition to the toolbox of dynamic covalent chemistry.

Fabrication and Evaluation of Gellan Gum/Hyaluronic Acid Hydrogel for Retinal Tissue Engineering Biomaterial and the Influence of Substrate Stress Relaxation on Retinal Pigment Epithelial Cells.

Cell therapies for age-related macular degeneration (AMD) treatment have been developed by integrating hydrogel-based biomaterials. Until now, cell activity has been observed only in terms of the modulus of the hydrogel. In addition, cell behavior has only been observed in the 2D environment of the hydrogel and the 3D matrix. As time-dependent stress relaxation is considered a significant mechanical cue for the control of cellular activities, it is important to optimize hydrogels for retinal tissue engineering (TE) by applying this viewpoint. Herein, a gellan Gum (GG)/Hyaluronic acid (HA) hydrogel was fabricated using a facile physical crosslinking method. The physicochemical and mechanical properties were controlled by forming a different composition of GG and HA. The characterization was performed by conducting a mass swelling study, a sol fraction study, a weight loss test, a viscosity test, an injection force study, a compression test, and a stress relaxation analysis. The biological activity of the cells encapsulated in 3D constructs was evaluated by conducting a morphological study, a proliferation test, a live/dead analysis, histology, immunofluorescence staining, and a gene expression study to determine the most appropriate material for retinal TE biomaterial. Hydrogels with moderate amounts of HA showed improved physicochemical and mechanical properties suitable for injection into the retina. Moreover, the time-dependent stress relaxation property of the GG/HA hydrogel was enhanced when the appropriate amount of HA was loaded. In addition, the cellular compatibility of the GG/HA hydrogel in in vitro experiments was significantly improved in the fast-relaxing hydrogel. Overall, these results demonstrate the remarkable potential of GG/HA hydrogel as an injectable hydrogel for retinal TE and the importance of the stress relaxation property when designing retinal TE hydrogels. Therefore, we believe that GG/HA hydrogel is a prospective candidate for retinal TE biomaterial.

Magma pressurization sustains ongoing eruptive episode at dome-building Soufrière Hills volcano, Montserrat

Abstract Dome-building volcanoes, where long-term eruptive episodes can be interspersed with periods of intra-eruptive repose, are particularly challenging for volcanic hazard assessment. Defining the end of eruptive episodes is vitally important for the socioeconomic recovery of affected communities but highly problematic due to the potential for rapid transition from prolonged, seemingly low-risk repose to dangerous effusive or explosive activity. It is currently unclear what constitutes the end of repose and an eruptive episode. We show that analysis of surface deformation can characterize repose and help define an eruptive episode. At Soufrière Hills volcano, Montserrat, the long-term post–2010 deformation at 12 continuous GPS stations requires the pressure in the magma system to have increased with time; time-dependent stress relaxation or crustal creep cannot explain the deformation trends alone. Continued pressurization within the magmatic system during repose could initiate a renewed eruption, qualifying as sustained unrest and therefore continuation of the eruptive episode. For Soufrière Hills volcano, persistent magma pressurization highlights the need for sustained vigilance in the monitoring and management of the volcano and its surroundings, despite the last eruptive activity ending in 2010. Our results show promise for application to other dome-building volcanoes.

Rheological Properties of Purple Avocado (Persea Americana Mill.) Fruits at Different Ripening Stages

Proper postharvest handling and management of perishable horticultural commodities require the proper understanding and the need for basic information on the mechanical properties of these commodities specifically for avocados to preserve quality and reduce losses and waste. Physical characterization and compression tests were conducted on avocados to develop an understanding of the rheological properties of avocados at different ripening stages, sizes, and compression loads. An appropriate equation in predicting volume from its weight and its shape signature that specifically represents the shape of the purple fruited avocado variety in a one-dimensional function were established. The shape of avocado fruits tends toward being spherical and expected to roll not slide as indicated by the mean values of sphericity and aspect ratio. The compressive strength of avocado varied with ripeness were small size can withstand up to 5 kg of load by weight after harvest without significant internal damage and 6 kg of load for medium size. Avocado fruits had a time-dependent stress relaxation behavior like other viscoelastic material. The threeterm Maxwell model with six parameters described the stress relaxation behavior of avocado fruit at different compressive loads, ripeness and sizes based on the maximum relative difference (MRD), R2 , and residual MSE. The advancing degree of ripeness have a corresponding decrease in the decay stress value (σ1) and time of relaxation (τ1) component of the model. To minimize mechanical damage, avocado should be packed in vertical orientation with cushion (bubble wrap, foam, or paper) and can be stacked up to 10 layers for small size and 12 layers for medium size at harvest using 10 kg capacity cartons.

Viscoelastic truss metamaterials as time-dependent generalized continua

Mechanical metamaterials provide tailorable functionality based on a careful combination of base material and structural architecture. Truss-based metamaterials, e.g., exploit structural topology and beam geometry to achieve beneficial mechanical and physical properties from stiffness and wave dispersion to strength and toughness. While the focus to date has been primarily on static metamaterial properties or elastic wave motion, 3D-printed polymeric base materials naturally come with significant viscoelasticity, making the effective truss response time- and rate-dependent. Here, we report a theoretical-numerical-experimental study which (i) deploys a linear viscoelastic corotational beam description (capturing finite rotations at small strains), (ii) implements the latter in a finite element framework, (iii) calibrates a generalized Maxwell model based on viscoelastic experiments on 3D-printed polymer samples, (iv) validates the theory and implementation through experimental truss benchmark tests, and (v) introduces a generalized continuum formulation for the efficient simulation of viscoelastic truss metamaterials containing large numbers of structural members. We show that the viscoelastic beam approach, calibrated via tension tests on individual strut samples, performs well when applied to complex truss lattices undergoing time-dependent stress relaxation — as verified by the effective mechanical response and full-field deformation maps. The resulting variational generalized continuum framework uses on-the-fly periodic homogenization based on a representative unit cell and is extended to dynamics by including inertial effects. By comparison to discrete numerical simulations we demonstrate the accuracy of the continuum approach, which is promising for modeling and optimizing 3D-printed truss metamaterials for engineering applications from shock-absorbing structures to rate-dependent architected materials and soft robotics.

Time-dependent springback prediction with stress relaxation effect for non-isothermal hot stamping of titanium alloy sheets

The hot stamping of titanium alloy sheets is a non-isothermal forming process due to the interfacial heat transfer while hot blank is formed and cooled in cold forming tools. Due to the condition of high temperature, the material experiences a thermal-mechanical coupled deformation and a time-dependent stress relaxation subsequently. The control on shape accuracy of hot-stamped titanium alloy parts is of great challenge owing to the complicated stress evolution mechanism. The accurate prediction of springback requires a comprehensive description on the temperature and strain rate sensitive deformation, and also on the stress relaxation during die quenching. The precise testing methods and constitutive models are crucial for accurate simulation. In this work, tensile tests with different temperature and strain rates, and stress relaxation tests with different temperature and initial stress levels are performed in Gleeble system. An integrated physically based constitutive model is developed to describe both the thermo-mechanical behavior and time-dependent stress relaxation in hot stamping process. Furthermore, the proposed model is implemented in the hot stamping simulations of U-shape part through user subroutines. The essential effect of stress relaxation on stress evolutions of U-shape part is analyzed. The simulation results show promising agreement with experiments when stress relaxation is taken into account. Finally, based on the principle of increasing temperature to enhance stress relaxation, increasing the forming speed is found to be an effective way to reduce the springback of titanium alloy in hot stamping.

Time dependent stress relaxation and recovery in mechanically strained 3D microtissues.

Characterizing the time-dependent mechanical properties of cells is not only necessary to determine how they deform but also to understand how external forces trigger biochemical-signaling cascades to govern their behavior. At present, mechanical properties are largely assessed by applying local shear or compressive forces on single cells grown in isolation on non-physiological 2D surfaces. In comparison, we developed the microfabricated vacuum actuated stretcher to measure tensile loading of 3D multicellular “microtissue” cultures. Using this approach, we here assessed the time-dependent stress relaxation and recovery responses of microtissues and quantified the spatial viscoelastic deformation following step length changes. Unlike previous results, stress relaxation and recovery in microtissues measured over a range of step amplitudes and pharmacological treatments followed an augmented stretched exponential behavior describing a broad distribution of inter-related timescales. Furthermore, despite the variety of experimental conditions, all responses led to a single linear relationship between the residual elastic stress and the degree of stress relaxation, suggesting that these mechanical properties are coupled through interactions between structural elements and the association of cells with their matrix. Finally, although stress relaxation could be quantitatively and spatially linked to recovery, they differed greatly in their dynamics; while stress recovery acted as a linear process, relaxation time constants changed with an inverse power law with the step size. This assessment of microtissues offers insights into how the collective behavior of cells in a 3D collagen matrix generates the dynamic mechanical properties of tissues, which is necessary to understand how cells deform and sense mechanical forces in vivo.

A coupled multi-scale method for predicting the viscoelastic behavior of resin-based 3D braided composites

A new alternative multi-scale calculation procedure was presented to characterize the time-dependent viscoelastic behaviors of resin-based three dimensional (3D) braided composites. The present investigation was processed based on micro-scale fiber/resin, meso-scale yarn/resin and macro-scale homogeneous composite. Integrating with the asymptotic expansion homogenization (AEH) method, the multi-scale physical fields in the three-scales is established, and the multi-phase finite element (MFE) method is adopted to overcome the difficulty in discretization for the heterogeneous structural models. The time-dependent stress relaxation responses under three-scales were particularly investigated by the coupling MFE-AEH multi-scale method. The time-dependent effective viscoelastic properties in the micro-sclae and meso-scale were also calculated by utilizing the Prony Series fitting to simplify the inverse Laplace transform. The accuracy and reliability are validated by the corresponding experimental and numerical results, the effects of braided angle and relaxation time on the viscoelastic properties of 3D braided composites were studied, respectively.

Improved distortion prediction in additive manufacturing using an experimental-based stress relaxation model

In additive manufacturing (AM), numerous thermal cycles make stress relaxation a significant factor in affecting the material mechanical response. However, the traditional material constitutive model cannot describe repeated annealing behavior. Here, we propose an improved constitutive model based on a serial of stress relaxation experiments, which can descript the temperature and time-dependent stress relaxation behavior during AM. By using the proposed relaxation model, the prediction accuracy is significantly improved due to the recovery of inelastic strain during multilayer deposition. The results are validated by both in-situ and final distortion measurements. The influence mechanism of the relaxation behavior on material mechanical response is explained by the three-bar model in thermo-elastic-plastic theory. The relaxation behavior during the whole AM process is clarified. The stress behavior is found to have a limited effect when merely depositing several layers; nevertheless, it becomes a prominent impact when depositing multiple layers. The proposed model can enhance modeling accuracy both in AM and in multilayer welding.

Using fractional derivatives for improved viscoelastic modeling of textile composites. Part II: Fabric under different temperatures

An improved modelling of the viscoelastic behavior of fabric composites at different temperatures is presented by a new means of fractional calculus. To this end, a four-parameter fractional derivative Zener model is first used to describe the dynamic behavior of the fabric, where the constitutive relation’s response to a unit step of strain (for determination of the time dependent stress relaxation modulus) can be readily found in the literature. This response function is then fitted to the experimental data of samples of a typical prepreg composite made of E-glass fibers comingled with polypropylene fibers, both at the dry and consolidated conditions. It is shown that the Zener model can better capture the experimental data when compared to the conventional approaches such as integer order modelling and Prony series. The results, particularly, showed that the viscoelastic behavior of the material at lower temperature regimes is far more accurate using the fractional derivatives approach. Finally, the variation of storage and loss moduli of the dry fabric with external cyclic loading were scrutinized, to determine the rubbery and glassy regions of the frequency response.

Modeling dynamic spherical cavity expansion in elasto-viscoplastic media

In this paper, we extend the dynamic spherical cavity expansion model for rate-independent materials developed by Durban and Masri (Int J Solids Struct 41(20):5697–5716, 2004), Masri and Durban (J Appl Mech 72(6):887–898, 2005), and Cohen et al. (J Appl Mech 77(4):041009, 2010) to viscoplastic media. For that purpose, we describe the material behavior with an isotropic Perzyna-type overstress formulation (Perzyna in Q Appl Math 20:321–332, 1963; Adv Appl Mech 9:243–377, 1966) in which the material rate dependence is controlled by the viscosity parameter $$\eta $$. The theoretical predictions of the cavity expansion model, which assumes that the cavity expands at constant velocity, are compared with finite element simulations performed in ABAQUS/Explicit (Abaqus Explicit v6.13 User’s Manual, ABAQUS Inc., Richmond). The agreement between theory and numerical simulations is excellent for the whole range of cavitation velocities investigated, and for different values of the parameter $$\eta $$. We show that, as opposed to the steady-state self-similar solutions obtained for rate-independent materials (Durban and Masri 2004; Masri and Durban 2005; Cohen et al. 2010), the material viscosity leads to time-dependent cavitation fields and stress relaxation as the cavity enlarges. In addition, we also show that the material viscosity facilitates to model the shock waves that emerge at the highest cavitation velocities investigated, controlling the amplitude and the width of the shock front.

Time-Dependent Testing Evaluation and Modeling for Rubber Stopper Seal Performance.

Sufficient rubber stopper sealing performance throughout the entire sealed product life cycle is essential for maintaining container closure integrity in the parenteral packaging industry. However, prior publications have lacked systematic considerations for the time-dependent influence on sealing performance that results from the viscoelastic characteristics of the rubber stoppers. In this paper, we report results of an effort to study these effects by applying both compression stress relaxation testing and residual seal force testing for time-dependent experimental data collection. These experiments were followed by modeling fit calculations based on the Maxwell-Wiechert theory modified with the Kohlrausch-Williams-Watts stretched exponential function, resulting in a nonlinear, time-dependent sealing force model. By employing both testing evaluations and modeling calculations, an in-depth understanding of the time-dependent effects on rubber stopper sealing force was developed. Both testing and modeling data show good consistency, demonstrating that the sealing force decays exponentially over time and eventually levels off because of the viscoelastic nature of the rubber stoppers. The nonlinearity of stress relaxation derives from the viscoelastic characteristics of the rubber stoppers coupled with the large stopper compression deformation into restrained geometry conditions. The modeling fit with capability to handle actual testing data can be employed as a tool to calculate the compression stress relaxation and residual seal force throughout the entire sealed product life cycle. In addition to being time-dependent, stress relaxation is also experimentally shown to be temperature-dependent. The present work provides a new, integrated methodology framework and some fresh insights to the parenteral packaging industry for practically and proactively considering, designing, setting up, controlling, and managing stopper sealing performance throughout the entire sealed product life cycle.LAY ABSTRACT: Historical publications in the parenteral packaging industry have lacked systematic considerations for the time-dependent influence on the sealing performance that results from effects of viscoelastic characteristic of the rubber stoppers. This study applied compression stress relaxation testing and residual seal force testing for time-dependent experimental data collection. These experiments were followed by modeling fit calculations based on the Maxwell-Wiechert theory modified with the Kohlrausch-Williams-Watts stretched exponential function, resulting in a nonlinear, time-dependent sealing force model. Experimental and modeling data show good consistency, demonstrating that sealing force decays exponentially over time and eventually levels off. The nonlinearity of stress relaxation derives from the viscoelastic characteristics of the rubber stoppers coupled with the large stopper compression deformation into restrained geometry conditions. In addition to being time-dependent stress relaxation, it is also experimentally shown to be temperature-dependent. The present work provides a new, integrated methodology framework and some fresh insights to the industry for practically and proactively considering, designing, setting up, controlling, and managing of the stopper sealing performance throughout the entire sealed product life cycle.

Characterisation of static and dynamic responses of natural rubber bio-composites

Characterisation of static and dynamic behavioural are presented in this study of hybrid filled natural rubber. The hybrid filler consists of a combination of oil palm ash (OPA) and egg shell powder (ESP). Testing on the samples are conducted in three different aspects namely static compression testing, time dependent stress relaxation testing in compression and dynamic compression testing. Mechanical properties such as the static stiffnesses, hysteresis loss ratios, stress relaxation responses, dynamic stiffnesses, phase angles and damping ratios are reported. The static stiffness values of the hybrid filled rubber, although lower than rubber filled carbon black, presented potential if the ESP content were to be increased. The stress relaxation responses lacked consistency in the uploading stages but were fairly consistent in the unloading stages where the relaxation was close to that of rubber filled carbon black. The dynamic properties appear to be no significant improvement over that of rubber filled carbon black filled. All hybrid filled rubber samples conformed to general dynamic properties of viscoelastic material and did not display any unexpected behaviour. Collectively, there is a trend of improvement with increasing ESP content but no prominent improvement over rubber filled carbon black is observed.

Stress evolution and whisker growth during thermal cycling of Sn films: A comparison of analytical modeling and experiments

Sn whiskers are a re-emerging reliability issue for Pb-free manufacturing. Although stress is considered as the most likely driving force for whisker formation, there is little quantitative understanding of how stress and whisker growth are correlated. To address this issue, we have developed an analytical model which accounts for strain generation (via thermal expansion mismatch) and multiple relaxation processes (rate-dependent plasticity and diffusion-controlled whisker growth). This model is used to analyze the results of thermal cycling experiments in which the evolution of stress and average volume of whiskers/hillocks were tracked as the features grew on the Sn surface. Predictions of the model are found to be in a good agreement with the time-dependent whisker growth and stress relaxation behaviors that have been observed in the experimental measurements.

Engineering estimation of time-dependent deformation characteristics as bending moment relaxation and released unfolding motion of creased paperboard

Paperboards are recognized to be important raw materials for packaging industry due to their advantages such as high strength-to-weight ratio, recyclability. Regarding the development of advanced packaging materials and the requirement of smart formed products, a study of sheet’s response behaviour is necessary for expanding the advanced converting industry. After introducing a couple of past research works concerned crease technologies, a fundamental mechanisms of crease deformation is reviewed using the scoring depth and the folding angle of a paperboard. Since one of important forming characteristics is a time-dependent stress relaxation or time-delayed strain during a fold/unfold process, the author’s experimental approaches for estimating a short term (less than 10 seconds) dynamic deformation behaviour of creased paperboard are discussed.

Thermal radiation effects on creep behavior of the turbine blade

Purpose– The purpose of this paper is to find the time dependent thermal creep stress relaxation of a turbine blade and to investigate the effect thermal radiation of the adjacent turbine blades on the temperature distribution of turbine blade and creep relaxation.Design/methodology/approach– For this analysis, the creep flow behavior of Moly Ascoloy in operational temperature of gas turbine in full scale geometry is studied for various thermal radiation properties. The commercial software is used to pursue a coupled fields analysis for turbine blades in view of the structural force, materials kinematic hardening, and steady-state temperature field.Findings– During steady-state operation, the thermal stress was found to be decreasing, whereas by considering the thermal radiation this rate was noticed to increase slightly. Also by increase of the distance between stator blades the thermal radiation effect is diminished. Finally, by decrease of the blade distance the failure probability and creep plastic deformation decrease.Research limitations/implications– This paper describes the effect of thermal radiation in thermal-structural analysis of the gas turbine stator blade made of the super-alloy M-152.Practical implications– Blade failures in gas turbine engines often lead to loss of all downstream stages and can have a dramatic effect on the availability of the turbine engines. There are many components in a gas turbine engine, but its performance is highly profound to only a few. The majority of these are hotter end rotating components.Social implications– Three-dimensional finite element thermal and stress analyses of the blade were carried out for the steady-state full-load operation.Originality/value– In the previous works the thermal radiation effects on creep behavior of the turbine blade have not performed.

3D printing of an interpenetrating network hydrogel material with tunable viscoelastic properties

Interpenetrating network (IPN) hydrogel materials are recognized for their unique mechanical properties. While IPN elasticity and toughness properties have been explored in previous studies, the factors that impact the time-dependent stress relaxation behavior of IPN materials are not well understood. Time-dependent (i.e. viscoelastic) mechanical behavior is a critical design parameter in the development of materials for a variety of applications, such as medical simulation devices, flexible substrate materials, cellular mechanobiology substrates, or regenerative medicine applications. This study reports a novel technique for 3D printing alginate-polyacrylamide IPN gels with tunable elastic and viscoelastic properties. The viscoelastic stress relaxation behavior of the 3D printed alginate-polyacrylamide IPN hydrogels was influenced most strongly by varying the concentration of the acrylamide cross-linker (MBAA), while the elastic modulus was affected most by varying the concentration of total monomer material. The material properties of our 3D printed IPN constructs were consistent with those reported in the biomechanics literature for soft tissues such as skeletal muscle, cardiac muscle, skin and subcutaneous tissue.

Numerical prediction and experiment on rubber creep and stress relaxation using time-dependent hyperelastic approach

Rubber is an excellent material for anti-vibration components in industry with a long term service. However, its time-dependent behaviour is undesirable in engineering applications. This article presents an engineering approach to evaluate the time-dependent responses, i.e., creep and stress relaxation, for rubber anti-vibration components. A time-dependent damage function was introduced into hyperelastic models. This function can be expressed in three forms. A typical rubber product and a dumbbell specimen were selected to validate the proposed approach. It has been shown that the predictions obtained from this method are consistent with the experimental data. It has also been established that the time-dependent response of industrial products can be predicted based on the responses from simple specimens, e.g., dumbbell specimen. In addition, it is possible to obtain a creep response based on a relaxation response and vice versa (by changing K value only) using the proposed approach, which has also been observed experimentally in the literature. The proposed function can also be easily incorporated into commercial finite element software (e.g., Abaqus). It has been demonstrated that the proposed method may be used at an appropriate design stage. Finally, the readers can select one of the three forms presented to perform assessments on the time-dependent responses evaluations for rubber anti-vibration products.

The contribution of time-dependent stress relaxation in protein gels to the recoverable energy that is used as a tool to describe food texture

The recoverable energy (RE), defined as the ratio of the work exerted on a test specimen during compression and recovered upon subsequent decompression, has been shown to correlate to sensory profiling of protein-based food products. Understanding the mechanism determining the time-dependency of RE is primordial. This work aims to identify the protein-specific impact on the recoverable energy by stress dissipation via relaxation of (micro)structural rearrangements within protein gels. To this end, caseinate and gelatin gels are studied for their response to time-dependent mechanical deformation as they are known to develop structurally distinct network morphologies. This work shows that in gelatin gels no significant stress relaxation occurs on the seconds timescale, and consequently no time-dependency of the amount of energy stored in this material is observed. In caseinate gels, however, the energy dissipation via relaxation processes does contribute significantly to the time-dependency of reversible stored energy in the network. This can explain the obtained RE as a function of applied deformation at slow deformation rates. At faster deformation, an additional contribution to the dissipated energy is apparent, that increases with the deformation rate, which might point to the role of energy dissipation related to friction of the serum entrapped by the protein-network. This work shows that engineering strategies focused on controlling viscous flow in protein gels could be more effective to dictate the ability to elastically store energy in protein gels than routes that direct protein-specific aggregation and/or network-assembly.