Axial Prestress Research Articles

Biomechanical effects of hemin and sildenafil treatments on the aortic wall of chronic-hypoxic lambs.

Introduction: Gestation under chronic hypoxia causes pulmonary hypertension, cardiovascular remodeling, and increased aortic stiffness in the offspring. To mitigate the neonatal cardiovascular risk, pharmacological treatments (such as hemin and sildenafil) have been proposed to improve pulmonary vasodilation. However, little is known about the effects of these treatments on the aorta. Therefore, we studied the effect of hemin and sildenafil treatments in the aorta of lambs gestated and raised at highlands, thereby subjected to chronic hypoxia. Methods: Several biomechanical tests were conducted in the descending thoracic aorta (DTA) and the distal abdominal aorta (DAA), assessing 3 groups of study of hypoxic animals: non-treated (Control) and treated either with hemin or sildenafil. Based on them, the stiffness level has been quantified in both zones, along with the physiological strain in the unloaded aortic duct. Furthermore, a morphological study by histology was conducted in the DTA. Results: Biomechanical results indicate that treatments trigger an increment of axial pre-stress and circumferential residual stress levels in DTA and DAA of lambs exposed to high-altitude chronic hypoxia, which reveals a vasodilatation improvement along with an anti-hypertensive response under this characteristic environmental condition. In addition, histological findings do not reveal significant differences in either structure or microstructural content. Discussion: The biomechanics approach emerges as a valuable study perspective, providing insights to explain the physiological mechanisms of vascular function. According to established results, alterations in the function of the aortic wall may not necessarily be explained by morphostructural changes, but rather by the characteristic mechanical state of the microstructural components that are part of the studied tissue. In this sense, the reported biomechanical changes are beneficial in mitigating the adverse effects of hypobaric hypoxia exposure during gestation and early postnatal life.

Piezoelectric energy harvester for wind turbine blades based on bistable response of a composite beam in post-buckling

A bistable piezoelectric energy harvester (PEH) is presented for harvesting power from vibrations occurring at low frequencies, as is the case of wind turbine blades. The axial compressive prestress of a piezoelectric composite beam at post-buckling serves as the bistability source, leading to high mechanical to electric power conversion. An in-house harvesting circuit connected to the piezoelectric terminals is used for demonstration of its harvesting power capabilities. A finite element (FE) model is used to analyze and optimize the coupled nonlinear electromechanical response of the PEH, including structure and circuit. A physical prototype has been manufactured and tested for validation of the electromechanical design and the FE modeling approach. Predictions and measurements indicate an increase of harvested power with applied prestress up to a transition point, where a sudden drop in power occurs. Good comparison between numerical and experimental results verified the modeling approach, whereas deviations related to physical boundary conditions at large compressive forces affected the prediction of the transition point in harvested power. The harvester produced 1.32 mW of electrical power under tonal base excitation of 1 g at 8 Hz. Hence, the nonlinear PEH has demonstrated its capability to harvest energy at frequencies much lower than its first linear modal frequency and could thus serve as a promising solution for powering IoT devices and sensors in large vibrating structures.

Free vibration analysis of fiber-reinforced composite multilayer cylindrical shells under hydrostatic pressure

With the development and application of composite materials in deepwater submersibles, the influence of high external pressure from deepwater environments on the vibration characteristics of composite pressure-resistant cylindrical shells cannot be ignored. In this paper, the free vibration characteristics of prestressed composite multilayer shells are methodically examined by establishing partial differential equations based on the three-dimensional elasticity theory. To solve these equations, the state-space technique and double Fourier series expansion are employed to transform them into state-space ordinary differential equations. These equations are utilized to analyze vibration problems of simply supported composite multilayer cylindrical shells with arbitrary layered angles. The initial stress equilibrium equation is solved to determine the prestress induced by the hydrostatic pressure. This overcomes the limitation of membrane stress and considers non-uniform distributions of radial and interlaminar prestresses. The proposed theoretical model and solution strategies are validated by comparing with theoretical and experimental results from the existing literature and the finite element method. Additionally, the present investigation reveals that the natural frequencies of thick shells can be calculated more accurately using the prestress derived by the proposed approach, especially subjected to noticeable hydrostatic pressure. Finally, the performed investigations indicate that the circumferential prestressing has a more pronounced effect on the shell's natural frequencies than axial prestressing.

Dynamic mechanical behavior of sandstone with filled joints at varying angles under coupled triaxial static and dynamic loading

Natural or artificially formed rock composite structures with consecutively filled joints at varying angles are frequently disturbed by coupled static and dynamic loads. Understanding the impacts of the confining pressure and joint angle on the dynamic mechanical behavior of rocks is important for the stability of rock mass engineering structures. In this study, seven joint angles and four confining pressures were considered. Dynamic triaxial compressive tests of sandstone with consecutively filled joints were conducted using a split Hopkinson bar (SHPB) apparatus. The test results showed that varying degrees of “strain rebound” phenomena were observed in the stress–strain curves, implying that the jointed samples in the failure stage could still store more elastic energy, which may trigger rock burst accidents in practical engineering. Moreover, the dynamic compressive strength and elastic deformation modulus were proportional to the confining pressure, but showed a trend of slight decrease followed by a noticeable increase with an increase in the joint angle from 0° to 90°. The combined effects of axial pre-stress and confining pressure resulted in different trends in the dynamic peak strain. The plastic deformation moduli of samples with smaller joint angles were insensitive to changes in the confining pressure and smaller joint angles, whereas those of samples with larger joint angles were sensitive to changes in the confining pressure and larger joint angles. In addition, the experimental tendency of the dynamic compressive strength under coupled triaxial static and dynamic loading was in good agreement with the theoretical derivation.

Seismic behavior of precast columns with unbonded prestressed tendons and energy-dissipating bars: physical and numerical investigations

The study of the strength and failure modes of construction components has become increasingly important with the advent of industrialized construction. Recently, because of the need to promote the survivability of both structures and persons, it has encompassed failure modes associated with seismic threats. This study reports the seismic behavior of precast segmented columns designed with both unbonded prestressed tendons (UPTs) and energy-dissipating (ED) bars. A physical specimen was subjected to a quasi-static cyclic test; this permitted the evaluation of the damage mode and behavior of the energy dissipation mechanism, and permitted the establishment and verification of a fiber beam element simulation model. The model was then used to evaluate the effects of the variation of the design parameters on the behavior of precast assembled columns. The test specimen exhibited stable energy dissipation and a pinching effect during cyclic loading. An analysis using the fiber beam element model with varying design parameters revealed that high-strength concrete could mitigate the concrete damage and residual deformation after an earthquake, and that the concrete strength and steel bar strength should be matched when enhancing the seismic resilience of precast columns with high-strength steel bars. It was determined that increasing the prestress mechanism, namely the ratio of the UPTs, could greatly improve the residual deformation, while the ratio of ED bars is the key factor in enhancing the energy dissipation capacity of the precast columns. Suitable ratios of UPTs and ED bars are the keys to ensuring stable energy dissipation and low residual drifts. Moreover, an increased axial load ratio and prestress level are able to restrain the joint opening and improve the bearing capacity of the precast columns; however, an excessive axial load or prestressing force would result in the rapid degeneration of the carrying capacity and larger residual displacements.

Seismic response of prestressed precast reinforced concrete beam-column joints assembled by steel sleeves

A novel prestressed precast reinforced concrete (RC) beam-column joint, composed of prestressed tendons, stiffened steel sleeves, and high-strength bolts, having improved self-centring ability and assembly efficiency is proposed in this paper. Four prestressed precast RC joints assembled by steel sleeves and one cast-in-place RC joint were tested under cyclic loading to investigate the seismic response of the proposed joint. The main parameters studied are the axial compression ratio of columns, stirrup ratio in the core area of the proposed joint and effective prestress of tendons. The energy dissipation capacity, bearing capacity, and self-centring ability of the prestressed precast RC beam-column joints assembled by steel sleeves are higher than those measured for the cast-in-place RC joint. For the prestressed precast RC joints assembled by steel sleeves, both yield and ultimate displacements increase with the increase of the axial compression ratio, stirrup ratio and effective prestress, but the ductility decreases with the increase of the axial compression ratio and effective prestress. The increasing of axial compression ratio can lead to an increase in the energy dissipation capacity, shear capacity and residual displacement. Finally, formulae to predict the shear capacity of prestressed precast RC joint assembled by steel sleeves are proposed, being in good agreement with the experimental results.

Experimental Determination of the Coefficient of Friction on a Screw Joint

This paper deals with the coefficient of determination of screw connection friction between the thread and the matrix. The coefficient of friction was measured using a laboratory device with an M20 screw connection without any grease and, subsequently, plastic grease was added (CX80 silicone, lithium, and copper grease). When grease is added, the friction in the threads and screw heads is limited and consistently retained. When tightening by torque, which represents the prevailing assembly method in standard screwing practice, only part of the torque is effectively used to create axial force and pre-stress. The rest of the torque is employed in friction suppression between threads and converted into heat. In general, the coefficient of friction depends on diverse factors such as the roughness of the thread surface, the gradient angle of the helix, and the grease properties. The tightening torque represents a primary parameter in the experimental measurements, monitored using a digital torque spanner, and generates an axial force in the screw. Based on the aforementioned parameters, the objective of this paper was to monitor changes in the coefficient of friction between the thread of the screw and the matrix in the case of different grease types. The actual coefficient of friction was calculated through the exponential equation of the torque balance. First measured was the load of the bolted joint without the use of grease, where the average value of the coefficient of friction was 0.44732; this value served as a benchmark for comparison to the measurements with the use of grease. The measurements showed that the value of the friction coefficient was reduced by 30.57% when using lithium grease, by 40.56% when using silicone grease, and by 47.64% when using copper-based grease, making the latter the most suitable for the application. Without appropriate greasing, friction suppression was accompanied by extremely high torques, which resulted in insufficient screw prolongation.

Dynamic progressive fracture behavior of axially confined sandstone specimens containing a single flaw

Rock masses are frequently subjected to dynamic disturbance in addition to pre-stress, which plays a key role in the stability and safety of underground projects. In this paper, the effects of flaw inclination angle and pre-stress on the mechanical properties and fracture behavior of sandstone specimens under repetitive impact loadings were investigated through a series of laboratory tests using a modified split Hopkinson pressure bar (SHPB) system. The results show that the dynamic strength decreases gradually with the increasing repetitive impact number. A larger flaw inclination angle produces fewer repetitive impacts for a given axial pre-stress. The repetitive impact counts and the cumulative absorbed energy peak at an axial pre-stress of 20–40 MPa. By the digital image correlation (DIC) technique, high strain localizations around the flaw periphery can be observed after the application of pre-stress. During the repetitive impact loadings, wing and anti-wing cracks occupy the dominant position. Compressive cracks also contribute to the ultimate failure if the specimen is subjected to solely repetitive impacts. Except for 90° specimens, shear cracks make a difference as well in the cracking process as the pre-stress increases.

Blast energy absorption in topological interlocking elastic columns

This study investigates blast dynamics of prestressed segmented columns assembled of osteomorphic interlocking elastic blocks without any binding materials or mechanical connectors. The unique ability of the interlocking structures to absorb and dissipate energy through the independent movement of their segments is analyzed using the nonlinear finite element method. The effects of the number of blocks, the axial prestress, the friction, and the level of interlocking between the contact surfaces on the flexural response and energy absorption capability of the segmented column are investigated parametrically. It is demonstrated that the detachments between blocks control the energy absorption capability of these structures. Therefore, the number of blocks, the axial prestress, and the level of interlocking (i.e., the parameters influencing the available detachment between blocks) define the response of this column to blast loads. Columns segmented into a greater number of blocks with lower prestress levels exhibit a higher damping capability but reduced column stiffness, which is usually undesirable in structural applications. A higher level of interlocking between the contact surfaces of blocks increases the damping capacity of the column without reducing its stiffness. The effect of friction is found to be insignificant for all cases considered. The effect of interlocking is small relative to the effects of prestress and the number of blocks. However, it provides an independent design parameter for the passive mitigation of blast loads.

Experimental Study on Mechanical Properties and Failure Laws of Granite with Artificial Flaws under Coupled Static and Dynamic Loads.

Rock is the main construction material of rock engineering, such as the engineering of mines and tunnels; in addition, its mechanical properties and failure laws are of great significance to the stability evaluation of rock engineering, especially under the conditions of coupled static–static stresses. In this study, granite specimens were manufactured with artificial flaws. Coupled static and dynamic loads tests were carried out with a modified split Hopkinson pressure bar (SHPB) apparatus; and six typical levels of axial pre-stresses and three crack inclination angles were designed. Three-dimensional digital image correlation (3D-DIC) was also applied to record and analyze the fracturing process and damage evolution of the specimens. The test results show that there was no compaction stage in the stress–strain curve under combined dynamic and static loading. The dynamic strength of the specimens increased first and then decreased with the increase in the static pressure; moreover, the specimens reached the maximum dynamic strength when the static pressure was 10% UCS. The dynamic strength decreased first and then increased with the increase in the crack inclination angle; and the lowest strength appeared when the inclination angle was 45°. The change in axial compression had a significant influence on the failure mode, and the failure mode gradually transformed from shear–tensile failure to shear failure with the increase in the pre-stress. The tensile strain was usually generated at the end of the fractures or near the rock bridge. When the axial pressure was small, the tensile strain zone parallel to the loading direction was easily generated; and when the axial pressure was large, a shear strain zone developed, extending along the diagonal direction. The research results can provide a theoretical reference for the correct understanding of the failure mechanisms of granite and its engineering stability under actual conditions.

Experimental investigation on the dynamic mechanical properties and energy absorption mechanism of foam concrete

For the construction of the deep-buried and super-long tunnels in an active tectonic zone, it is crucial to explore the dynamic mechanical properties and energy absorption mechanism of foam concrete (FC). In this study, splitting Hopkinson pressure bar (SHPB) tests were carried out with five different dry densities (DD) of FC. The influences of strain rate and DD on the dynamic mechanical properties of FC were analyzed based on the peak stress, stress–strain curve, energy absorption and failure mode. Finally, the energy absorption mechanism of FC and the influence of axial pre-stress on the energy absorption were discussed. The results show that the peak stresses of FC have a linear relation with strain rate. Furthermore, the dynamic stress–strain curve of FC has evident fluctuation characteristics, and the fluctuation is more prominent with a smaller DD. For FC with the same DD, the energy absorption rate (EAR) initially increases and then decreases with the increase of the incident energy. Whereas, the largest EAR of FC is achieved with the smallest DD. The energy absorption mainly depends on the compaction of pores for FC with the small DD, while the expansion of pores and new cracks is attained by FC with large DD. The pre-stress (less than 70% of the uniaxial compressive strength (UCS)) may enhance the EAR of FC. However, FC begins to release energy when the pre-stress reaches 90% of UCS.

Experimental and numerical investigation on the mechanical responses and cracking mechanism of 3D confined single-flawed rocks under dynamic loading

Accurately characterizing the mechanical responses and cracking mechanism of three-dimensional confined fractured rocks under coupled static-dynamic loading is of paramount importance for underground engineering construction. Using a modified split Hopkinson pressure bar (SHPB) system, five groups of single-flawed specimens with the axial prestress ratio from 0 to 0.8 are tested at the strain rates in the range of 65–205 s−1 under a fixed radial prestress. Our results indicate that both the dynamic strength and total strength show significant positive linear correlations with the strain rate, and the dynamic strength shows more strain rate sensitivity under higher axial prestress. The dynamic strength and corresponding failure strain decrease with increasing axial prestress, while the total strength is barely affected by the axial prestress. The dynamic elastic modulus initially increases before the axial prestress ratio reaches 0.6 and then decreases. The failure pattern of tested specimens changes from single diagonal failure to an “X” shaped conjugated failure as axial prestress increases. Furthermore, the progressive cracking processes of confined single-flawed specimens under different axial prestresses are numerically visualized by the discrete element method (DEM). Based on the displacement trend lines on both sides of cracking surface, five crack types are identified and classified in our simulation. The displacement field distributions of the DEM models reveal that the macroscopic single diagonal failure under lower axial prestress is mainly controlled by mixed tensile-shear cracks, while the “X” shaped conjugated failure under higher axial prestress is shear dominated.

Surface tension-driven instability of a soft elastic rod revisited

Surface tension-driven morphological instability of a soft (compressible or incompressible) linearly elastic rod is studied based on the Gurtin–Murdoch (GM) theory of surface elasticity. This study is inspirited by instability of shorter wavelength observed in some experiments which are not covered by the existing linear elastic models. Here, unlike the original GM model, the present model addresses the influence of surface tension-induced bulk residual stress on the incremental bulk stress associated with instability. The relation between the dimensionless ratio σ0/(μR) (where σ0, μ and R are surface tension, shear modulus and radius of the rod) and the unstable mode’s wavelength λ is studied based on the present model and the GM model, with comparison to the known results given by the existing linear elastic models. Different than the existing linear elastic models which predict the instability only if σ0/(μR) ≥ 6 with the wavelength λ/(2R) > π, the present model and the GM model predict the instability with lower surface tension and much shorter wavelengths (e.g. λ/(2R)≈1.5), which could offer a plausible explanation for instability observed in some experiments. In addition, the effects of a bulk axial prestress and the Poisson ratio on the surface tension-induced instability of a soft linear elastic rod are examined..

Experimental study of the mechanical and fracture behavior of flawed sandstone subjected to coupled static-repetitive impact loading

In nature, rock masses, particularly underground rock structures, are subjected not only to static stress but also to frequent dynamic disturbances. In this paper, dynamic tests were carried out on single flawed sandstone specimens using a split Hopkinson pressure bar (SHPB), aiming to investigate the mechanical and fracture behavior of fractured rocks subjected to coupled static-repetitive impact loading. The results show that the dynamic strength of the flawed specimens decreases gradually with increasing the flaw length and repetitive impact number. The flaw length and axial prestress significantly affect the dynamic mechanical behavior of the flawed specimens. A longer flaw length produces lower dynamic strength and fewer repetitive impacts for a given axial prestress. The repetitive impact counts and the cumulative absorbed energy peak at an axial prestress of 20 MPa. Tensile strain, characterized by the digital image correlation (DIC) technique, is concentrated on the flaw tips and progressively extends approximately along the loading direction with increasing repetitive numbers. Wing and anti-wing cracks are the dominant cracks under repetitive impact loading conditions. Under repetitive impact without axial prestress, wing cracks play a key role in the failure of the specimen, while anti-wing cracks dominate the fracture process when the specimens are subjected to coupled static-repetitive impact loading. The findings in this paper could deepen the knowledge of the mechanical and fracture behavior of rocks subjected to coupled static-repetitive impact loading.

Experimental and Numerical Investigation on the Dynamic Failure Envelope and Cracking Mechanism of Precompressed Rock under Compression-Shear Loads

The complex response of underground geomaterials subjected to dynamic disturbance arises from the microstructure redistribution under high in- situ stress and the resulting fracture behaviors at multiaxial stress states. Inclined specimens were employed in an axially constrained split Hopkinson pressure bar (SHPB) system to achieve a combination of compression-shear stress states and static-dynamic loads. The loading rate under investigation ranged from 500 to 4,000 GPa/s, along with the axial prestress of 7, 21, 35, 49, and 63 MPa on specimens with an inclination of 0°, 3°, 5°, and 7°. The modified SHPB experimentation and discrete-element method modeling were implemented to unravel the combined effects of the loading rate, preload, and stress path on the failure mechanism of sandstone specimens involving the failure strength and envelope, fracturing pattern, fragmentation, and microcracking process. The positive rate dependence of the failure strength and Drucker–Prager envelope was observed. The preload showed double effects on the failure strength, indicated by an upper bound of the failure envelope as it expanded with the increasing preload. The microdamage accumulated during preloading and the global stress field collectively influenced the failure pattern of the inclined specimen, altering from a shear fracturing mode under dynamic loading or high-preload static-dynamic loading to an axial splitting mode near the specimen surface under low-preload static-dynamic loading.

Single Electrode Bidirectional Switching of Latchable Prestressed Bistable Micromechanical Beams

Electrostatically actuated, bistable, curved micromechanical beams can exhibit latching, wherein the beams remain in two distinct stable states without an applied voltage. These structures could serve as building blocks in a variety of applications such as micromechanical logic elements, switches, non-volatile memories, and low power consumption sensors. However, the design of such devices is challenging since such structures are prone to symmetry breaking, which consequently inhibits latching. Generally, asymmetric responses may be circumvented by introducing a tailored axial compressive prestress. In this work we explore, both theoretically and experimentally, the influence of prestress on the single electrode, bidirectional dynamic switching of curved, latchable, single crystal Si <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\approx 1000 \;\mu \text{m}$ </tex-math></inline-formula> long and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\approx 3.5\;\mu \text{m}$ </tex-math></inline-formula> wide beams. We use Joule heating to apply the necessary prestress required to eliminate symmetry breaking and ensure latching. In accordance with reduced-order model predictions, our experimental findings show that prestress plays a key role in the dynamic response of the beam. Our results demonstrate bidirectional operation using a single electrode, fostering a compact footprint device for tailoring the axial stress and dynamic conditions.

A novel and robust technique for identifying prestress forces in prestressed concrete beams using generic finite elements and simulated annealing algorithms

This work presents a novel technique for estimating the prestressing forces in simply supported beams with axial prestress force. The technique is based on the use of generic finite elements for modeling the beam and experimental time-domain response to simultaneously identify axial forces and generic parameters. Parameter updating is accomplished using a Simulated Annealing algorithm implemented for the solution of the prestress force identification problem. The effectiveness of the method was assessed in numerical simulations and was further verified on an experimental prestressed concrete beam. The results show that the inclusion of generic elements allows the identification of the force to be achieved even in the presence of errors in model parameters, thus eliminating the restraints of previous approaches.

Failure characteristics of brittle rock containing two rectangular holes under uniaxial compression and coupled static-dynamic loads

To deeply understand the failure characteristics of defective rock under actual stress condition, impact tests were conducted on prismatic granite containing two rectangular holes with different axial static pre-stresses by a modified split Hopkinson pressure bar (SHPB), and uniaxial compression tests were also carried out for comparison. Combined with digital image correlation (DIC), the dynamic damage and fracture process of specimens were observed by low-speed and high-speed cameras. Moreover, the energy evolution characteristics of specimens were analyzed to further understand the failure mechanism. The results indicate that the pre-stress has dual effects on the dynamic mechanical behavior of rock specimens, and the transition mechanism of the effect of pre-stress can be revealed by the elastic deformation limit. Observations show that the failure of specimens under different loads is caused by the growth of secondary cracks at hole corners. However, with the increase in pre-stress, the crack mode tends to shear and the strain localization tends to concentrate on sidewalls, resulting in severe rock bursting and extensive fracturing. Four coalescence modes around two rectangular holes were summarized: diagonal shear coalescence under static load, no coalescence under dynamic load, shear coalescence inside the middle rock bridge area under the pre-stress of 25–55% UCS, and indirect coalescence outside the rock bridge area under the pre-stress of 75% UCS. The specimen with the pre-stress of 75% UCS releases the internal strain energy during dynamic failure process, while the specimen with lower pre-stress absorbs the external impact energy. Finally, some insights are provided for deep rock engineering based on the test results.

Effect of Filling on Failure Characteristics of Diorite with Double Rectangular Holes Under Coupled Static–Dynamic Loads

The effect of infilling on mechanical response and crack behavior of pre-stressed rock with double rectangular holes under dynamic load was investigated through a series of coupled static–dynamic loading tests on diorite specimens in three different filling states, i.e., no infilling, single infilling and double infilling, using a modified split Hopkinson pressure bar. The deformation, damage and fracture process of specimens were recorded and analyzed by low-speed and high-speed cameras with digital image correlation method. Test results reveal that under the same dynamic load, the strength of specimens increases first and then decreases with the increase of axial static pre-stress, and reaches the maximum under 25% UCS due to crack closure. The strengthening effect of double infilling on strength is much more significant than that of single infilling and increases with the pre-stress. Observations show that with the increase of pre-stress, the degrees of damage and strain localization of specimens increase, and the superficial damage on the free surface of sidewalls are more severe. The effect of infilling is significant on the crack initiation and propagation, especially on the inhibition of sidewall spalling, rock ejection and the axial displacement failure of rock septum between holes. With the increase of pre-stress, the failure pattern and the crack coalescence mode change from obvious tensile to shear, and the coalescence position changes from the inside to outside of the septum area. However, the change of filling state has little effect on the coalescence mode, only on the coalescence position.

Nonlinear Mechanical Properties of Prestressed Branched Fibrous Networks

Random fiber networks constitute the solid skeleton of many biological materials such as the cytoskeleton of cells and extracellular matrix of soft tissues. These random networks show unique mechanical properties such as nonlinear shear strain-stiffening and strain softening when subjected to preextension and precompression, respectively. In this study, we perform numerical simulations to characterize the influence of axial prestress on the nonlinear mechanical response of random network structures as a function of their micromechanical and geometrical properties. We build our numerical network models using the microstructure of disordered hexagonal lattices and quantify their nonlinear shear response as a function of uniaxial prestress strain. We consider three different material models for individual fibers and fully characterize their influence on the mechanical response of prestressed networks. Moreover, we investigate both the influence of geometric disorder keeping the network connectivity constant and the influence of the randomness in the stiffness of individual fibers keeping their mean stiffness constant. The effects of network connectivity and bending rigidity of fibers are also determined. Several important conclusions are made, including that the tensile and compressive prestress strains, respectively, increase and decrease the initial network shear stiffness but have no effect on the maximal shear modulus. We discuss the findings in terms of microstructural properties such as the local strain energy distribution.