Characterization Of Mechanical Behavior Research Articles

Comparative analysis of classic network vs. nanogel junction network in konjac glucomannan/kappa carrageenan hybrid hydrogels

The three-dimensional network architecture of hydrogels significantly influences their mechanical and physical properties; therefore, understanding them is essential for designing optimized hydrogel-based biomaterials. This study presents a comparative analysis of two hybrid hydrogels composed of konjac glucomannan (KGM) and kappa carrageenan (KCAR) with the same stiffness (5.2–5.7 kPa and 1.6–1.7 kPa) thus similar cross-linking density but different network architectures: a classic network formed by extended polysaccharide interactions and a nanogel junction network where nanoscale cross-linked KCAR (KCAR-NGs) links KGM chains. The mechanical behavior, dissolution, and diffusion characteristics were examined, revealing that the classic network demonstrates superior tensile resistance, elongation, and solvent-induced swelling resistance, leading to slower dissolution rates and higher viscosity. Conversely, the nanogel junction network offers higher permeability for small molecules and faster dissolution, suggesting a more open network structure. These findings highlight the nanogel-based hydrogels' advantages for biomedical applications requiring stability, permeability, and rapid dissolution without high temperatures or chelating agents. This study underscores the potential of nanogel junction networks to balance hydrogel stiffness and permeability, advancing the design of hydrogel-based biomaterials.

Off-axis mechanical behavior and dynamic characteristics of UHMWPE composite laminates

An understanding of the off-axis mechanical behavior and failure mechanisms of ultra-high molecular weight polyethylene (UHMWPE) cross-ply laminates subjected to quasi-static and dynamic loadings is developed, with focus on the influence of off-axis angle and strain rate. For off-axis tension, UHMWPE laminates exhibit polymer shear response characteristics. An orientation-hardening phenomenon is captured, as fiber rotation leads to local increment of load capacity along the loading orientation. The failure strength presents an evidentially descending trend with off-axis angle from 0° to 45°. A non-monotonic variation of strength with strain rate is further observed: increasing with strain rate up to 500 s−1 but decreasing above, which is attributed to failure mode switching from plastic failure to brittle failure. The Tsai-Wu failure criterion, on homogenized cross-ply laminae, is experimentally modified with rate dependence. Further investigation on detailed information of the unidirectional properties should be conducted with the backing-out scheme to establish unidirectional failure criterion.

Rate-dependent constitutive behavior and mechanism of CMDB under tension loading

The composite modified double-base propellants (CMDB) were experimentally investigated for mechanical behavior under wide tension strain rate loading from 0.0001 s-1 to 2500 s-1, based on Instron mechanical machine and modified Hopkinson tension bar technique. Stress-strain curves were obtained for its strain rate effect and integrality evaluation. The results indicated that CMDB presents high rate-dependence with flow stress distinctly increase as loading strain rate increasing. A succinct constitutive formulation is established with only five parameters, to characterize well the rate-dependence and strain hardening behavior. The fracture morphologies were investigated by scanning electron microscopy, and it is indicated that they are also rate-dependent: the cavitation and matrix damage induced from matrix deformation work less but more RDX particles fractures with strain rate increasing. Equivalent unit cell model with brittle cracking was established to simulate the mechanical behavior and failure characteristics of CMDB. The results reveal that with increasing loading strain rates, CMDB presents a tough-brittle transition, with less cavitation and matrix damage induced by matrix deformation, while more RDX particles fracture. Series of simulated results confirm qualitatively the experimental observations, and the obtained stress contours facilitate to validate the observed characteristics and propose reasonable mechanisms.

Analysis of failure properties of red sandstone with structural plane subjected to true triaxial stress paths

In order to study the mechanical behavior and failure characteristics of rock mass with the structural plane in complex deep stress environment, the QKX-YB200 true triaxial rockburst test system, acoustic emission, and digital video recorder were adopted to conduct true triaxial loading and unloading indoor tests on the red sandstone cube specimens. The results show that: (1) Under true triaxial loading conditions, all specimens propagate in the form of anti-wing crack, and the dip angle of the structural plane is linearly related to the average value of the anti-wing crack propagation angle; under true triaxial unloading conditions, the specimens with structural plane dip angles of 30°, 45°, and 60° propagates in the form of wing crack, while those with a 90° angle propagate anti-wing cracks, and the closure of structural plane is related to the the crack type at the tips of structural plane. (2) The unstable failure stages in the stress–strain curve under true triaxial unloading are longer and exhibit more pronounced fluctuations; the peak strength of the specimens under the conditions of true triaxial loading and unloading decrease first and then increase with the increase of the dip angle, reaching the lowest at 45°. (3) During the true triaxial unloading tests, the rockburst degree of the intact rock specimens is more violent than that of the specimens with a structural plane. Additionally, the dip angle of the structural plane influences the severity of rockbursts under the same stress path. (4) The crack propagation mechanism and the closure degree of structural planes under different true triaxial stress paths and dip angles are discussed. It is observed that the crack initiation mode around the structural plane tips and the crack mode near free surface are closely related to the stress environment in different areas of the specimens. (5) Based on the indoor test results and previous experimental data, the differences in peak strength characteristics between open structural planes and closed structural planes are preliminarily analyzed and compared.

Influence of Curing Time on the Mechanical Behavior of Cold Recycled Bituminous Mix in Flexible Pavement Base Layer

This study examined the mechanical behavior characteristics of cold recycled emulsified asphalt bases with RAP 76% and emulsified asphalt 3%, in different cure time, i.e., 0, 7, 14 and 28 days and evaluated in terms of the resilient modulus (RM) and permanent deformation (PD) based on repeated load triaxial tests. The results demonstrated that in the first 7 days, the RM increased by 80% compared to the freshly compacted material and after this period, the subsequent increases were not as significant, ranging, from 10.9% to 19.4%, that shows that initical cure time significantly influences the RM behavior of the mixtures. However, the mixtures showed considerable permanent deformations, even after 28 days of curing. This indicates that the use of asphalt emulsion, with prolonged curing, improves the mechanical properties of the mixture but does not entirely resolve the issue of permanent deformation in cold reclaimed asphalt mixture (CRAM). The plastic deformation behavior observed in the triaxial tests must be taken into account when designing pavements containing RAP and asphalt emulsion.

Characterization of mechanical behavior and cementing mechanism of high-strength composites using biomimetic chemically induced calcium carbonate precipitation method

Biomimetic mineralized mortar (BMM) represents a novel green cementitious material, increasingly recognized for its environmental sustainability. In this study, four typical amino acids including acidic amino acids (aspartic acid, glutamic acid), neutral amino acid (threonine), and basic amino acid (arginine), are employed as crystal modifiers to develop the high-strength BMM (HBMM) based on the biomimetic chemically induced calcium carbonate precipitation (BCICP) method. The mechanical properties and failure morphology of HBMM were evaluated through unconfined compressive strength (UCS) test. The microstructure characteristics of HBMM were investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and contact angle test. The results show that amino acid-modified calcium carbonate precipitation can effectively cement loose sand particles and significantly improve the strength of the HBMM. The failure modes of HBMM observed include local failure, vertical splitting failure, shear failure, and splitting-shear mixed failure. Notably, aspartic acid and glutamic acid can induce the formation of vaterite-phase calcium carbonate crystals, while threonine and arginine facilitate the formation of aragonite-phase calcium carbonate crystals. The hydrogen bonding between modified calcium carbonate crystals and silanol groups on the silica surface ensures a tight adhesion of the precipitate to sand surfaces, filling gaps and cementing particles. This study elucidates that using amino acids as modifiers in the BCICP method can significantly enhance the strength of HBMM and influence its microstructure, offering valuable insights for its potential practical applications.

Experimental study on effect of cyclic gas pressure on mechanical and acoustic emission characteristics of salt rock

The utilization of renewable resources like wind and solar energy has led the Chinese government to prioritize the development of energy storage systems, garnering significant attention for salt cavern compressed air energy storage (CAES) technology. The stability of the surrounding rock in salt caverns is critical for ensuring sustained operation. By conducting mechanical tests on salt rock under fixed axial and confining pressures with cyclic gas pressure, the mechanical behavior and acoustic emission characteristics of salt rock under the influence of gas pressure were analyzed. The mechanical and acoustic emission characteristics of salt rock were analyzed. The results indicated that the triaxial compressive strength of salt rock negatively correlated with constant gas pressure. Both radial and axial strains demonstrated distinct phases: deceleration, steady-state, and acceleration. The steady-state creep rate of axial strain and the lower limit of cyclic gas pressure can be fitted in the form of an exponential function. The number of cyclic air pressure cycles decreased as the lower limit of cyclic air pressure increased. Acoustic emission count was used to define the damage variables, clarifying the formation and accumulation of salt rock damage in each stage, distinguishing the growth rates of damage during loading and unloading. It was observed that the higher the lower limit of cyclic air pressure, the quicker the damage accumulated with cycling. During the test, the absolute energy of the acoustic emissions from the salt rock conformed to a damped power-law distribution. The power-law distribution index γ of the absolute energy of acoustic emissions shifted with the number of cyclic air pressure cycles, and the sudden decrease of the distribution index γ plays a certain early warning role for the failure of salt rock.

Experimental Characterization of Anisotropic Mechanical Behaviour and Failure Mechanisms of Hardened Printed Concrete.

Extrusion-based printing of cementitious materials represents an innovative technology in civil engineering. The additive manufacturing process significantly influences the material properties in the hardened state, leading to anisotropic behaviour in terms of stiffness and strength compared to conventionally cast concrete. This experimental study aims to deepen the understanding of the mechanical behaviour of hardened printed concrete. Beam-like specimens with varying printing patterns, loading orientations and lengths are investigated within three-point bending tests (3PBT) and uniaxial compression tests (UCT). Homogenized material parameters such as Young's modulus, compressive and flexural tensile strength and density are statistically evaluated using optically measured displacement and strain fields on the specimen surface. The qualitative and quantitative results demonstrate a strong dependency of material properties and failure mechanisms on the printing pattern. The interfilamental and interlayer areas with weak adhesion are identified as the main reason for anisotropy.

Study on the mesoscopic mechanical behavior and damage constitutive model of micro-steel fiber reinforced recycled aggregate concrete

This study employs in-situ 4D CT experimental techniques to investigate the mesostructured changes and mechanical behavior of micro steel fiber-reinforced recycled aggregate concrete (MSF-RAC) under uniaxial compression and cyclic loading conditions. The research aims to address the scientific problem of limited understanding of how micro steel fibers affect the mesoscopic mechanical behavior and structural damage characteristics of recycled aggregate concrete. High-resolution CT scanning technology was utilized for real-time observation of crack initiation and propagation, revealing the micro-mechanisms by which micro steel fibers enhance RAC. The study found that incorporating micro-steel fibers significantly improves the density of the interfacial transition zone (ITZ), inhibits crack development, and enhances the mechanical properties of the concrete. Based on these observations, an improved stiffness degradation damage constitutive model was proposed, which comprehensively considers the distribution orientation of micro steel fibers and ITZ characteristics. The model effectively predicts the stress-strain relationship of MSF-RAC under various conditions, demonstrating high accuracy and practicality. These findings provide important theoretical support and experimental evidence for the optimal design of RAC, showcasing significant engineering application value by promoting the sustainable use of recycled materials in construction.

Investigating the Mechanical Behavior and Energy Absorption Characteristics of Empty and Foam-Filled Glass/Epoxy Composite Sections under Lateral Indentation.

In this study, the crashworthiness behavior and energy absorption capacity of composite tubes under lateral indentation by steel rods aligned parallel to the specimen axis are investigated using experimental methods. Key parameters such as tube diameter, length, wall thickness, and indenter diameter are systematically examined and compared. Additionally, the influence of polyurethane foam fillers on damage modes and energy absorption capacity is rigorously analyzed. Contrary to conventional findings, smaller diameter specimens filled with foam demonstrate superior energy absorption compared to their larger counterparts, primarily due to enhanced compression of the foam volume. Experimental results reveal a complex interplay of damage mechanisms in composite specimens, including matrix cracking, fiber breakage, foam crushing, foam densification, foam fracture, and debonding of composite layers, all contributing to enhanced energy absorption. Increased tube thickness, length, and indenter diameter, alongside decreased tube diameter, are correlated with higher contact forces and improved energy absorption. Smoother shell fractures are promoted, and overall energy absorption capabilities are enhanced by the presence of foam fillers. This investigation provides valuable insights into the structural response and crashworthiness of composite tubes, which is essential for optimizing their design across various engineering applications.

Mechanical behavior and energy characteristics of red sandstone with different seawater immersion heights under biaxial compression

Rock structures engineered during undersea mining are typically subjected to varying water distributions due to the motion of seawater, which considerably influences their stability. Hence, it is essential to understand the influence of seawater distribution on the mechanical behavior and energy characteristics of rocks. In this study, biaxial compression tests were conducted on red sandstone at various seawater immersion heights, and acoustic emission signals during compression were monitored. The results illustrate that the mechanical properties of the red sandstone deteriorate significantly upon seawater immersion. With an increase in seawater immersion height, the peak strength and elastic modulus of the rock specimens decreased exponentially. When the seawater immersion height was varied from 0 to 1/4 H under lateral stresses of 5, 10, 15, and 20 MPa, the peak strength decreased by 18.94%, 20.29%, 17.47%, and 14.87%, respectively, and the elastic modulus decreased by 4.6%, 8.1%, 11.7%, and 10.9%, respectively. Brittleness also decreased gradually. During compression, the acoustic emission (AE) and accumulated AE counts exhibited a stationary phenomenon, first increasing slowly and then suddenly. However, the AE counts decrease with increasing seawater immersion height. Meanwhile, with increasing seawater immersion height, the proportion of tensile cracks gradually increased and that of shear cracks gradually decreased. As the seawater immersion height increased, both the peak total input strain energy and peak total elastic strain energy decreased, whereas the peak total dissipated strain energy exhibited the opposite trend.

Temperature-dependent acoustic emission characteristics and statistical constitutive model of granite under uniaxial compression

Understanding the temperature-dependent mechanical behavior and fracture characteristics of granite is crucial for many engineering projects. In this study, the real-time temperature curves of granite specimens were obtained during the heating and cooling process, and the thermal treatment tests were conducted. The physical properties of the specimen before and after thermal treatment, including mass, volume, and P-wave velocity, were measured. The acoustic emission (AE) signal in the uniaxial compression is monitored. The results indicate that the physical properties of granite deteriorate with temperature, while the mechanical properties show two effects of thermal strengthening and thermal weakening. This phenomenon is comprehensively analyzed by literature statistical data and optical microscopic observation. Furthermore, the AE characteristic is strongly dependent on temperature. High temperature induces more AE ring count to appear in the early stage of loading. As the temperature increases, the crack initiation stress decreases and the table crack propagation stage becomes longer. The attenuation of high-frequency signals and the enhancement of low-frequency signals are related to the development and interaction mechanism of thermally-induced crack and stress-induced crack. At 600 °C, the global b-value increases significantly. Meanwhile, the evolution of dynamic b-value helps explain the failure process of granite under axial load after thermal treatment. In addition, a new thermo-mechanical damage statistical constitutive model of granite considering temperature effects is proposed by introducing AE parameters. The main advantages of this model can well fit the nonlinear behavior of granite in the early loading stage after thermal treatment, and reflect the failure process of granite before the peak value.

Study on interfacial mechanical properties of bonded pipe joint under dynamic load

This study analyses the interfacial mechanical behaviour of adhesive-bonded pipe joints under dynamic loading conditions. First, a mechanical model of the bonding interface of a pipe joint was established. Next, computational formula for the interfacial slip and shear stress in the pipe joints were obtained using variable separation, eigenfunction expansion, and Laplace transform methodologies. Further, the effects of various parameters, including the loading duration, bond length, adhesive layer thickness, stress rate, adhesive shear modulus, elastic moduli of the main pipe and coupler pipe, and adhesive-layer thickness, on the mechanical response of the pipe joints were assessed. The goal is to study the impact of these parameters on the maximum shear stress, interfacial slip, and normal stress in the main and coupler pipes, their effects on the pipe joint strength can be determined, thereby providing a theoretical basis for the design of practical pipe–joint configurations. The innovation of this study is as follows: it considers high-stress-rate dynamic loads for formulating complete mathematical equations. Further, it employs theoretical methods to calculate the relative slip and shear stress in pipe joints, through which theoretical formulas for engineering applications of adhesive-bonded pipe joints were derived. Additionally, the study analyses the impact of various parameters on the dynamic mechanical behaviour of the adhesive layer at the pipe joint interface, leading to a deeper understanding of the interface mechanical behaviour characteristics and key parameters to be considered while receiving dynamic loads in pipe joints.

Experimental and numerical analysis of Brazilian splitting mechanical properties and failure mechanism for composite discs

The properties of structural planes and the strength of rock matrix significantly influence the splitting characteristics of composite rock masses. To investigate the effects of structural plane and differences in matrix strength on the mechanical behavior and failure characteristics of composite jointed rock bodies, composite jointed disc specimens with varying structural plane roughness and matrix combinations were prepared. These specimens were then subjected to Brazilian split tests under different loading angles ranging from 0° to 90°. Results indicate that the failure mode of the specimens is determined by the angle of the structural plane. As the structural plane angle increases, the failure mode transitions from structural plane failure to combination failure and finally back to structural plane failure. Increased roughness of the structural plane reduces the extent of structural plane failure, while matrix strength has no significant impact on the failure mode. The failure load of the specimens increases with increasing structural plane angle, roughness, and matrix strength. The influence of structural plane roughness and matrix strength on the mechanical properties of the specimens grows with increasing structural plane angle. Increases in structural plane roughness and matrix strength significantly enhance the strain energy and dissipated energy of the disc model. Finally, an analysis of the stress state on the structural planes is combined with an exploration of the failure mechanisms of the specimens.

Investigate on the mechanical properties and microscopic three-dimensional morphology of rock failure surfaces under different stress states

The macro and micro morphology of rock failure surfaces play crucial roles in determining the rock mechanical and seepage properties. The morphology of unloaded deep rock failure surfaces exhibits significant variability and complexity. Surface roughness is closely linked to both shear strength and crack seepage behavior. Understanding these morphology parameters is vital for comprehending the mechanical behavior and seepage characteristics of rock masses. In this study, three-dimensional optical scanning technology was employed to analyze the micromorphological properties of limestone and sandstone failure surfaces under varying stress conditions. Line and surface roughness characteristics of different rock failure surfaces were then determined. Our findings reveal a critical confining pressure value (12 MPa) that influences the damage features of Ordovician limestone failure surfaces. With increasing confining pressure, pore depth and crack formation connecting the pores also increase. Beyond the critical confining pressure, the mesoscopic roughness of the failure surface decreases, and the range of interval-distributed pore roughness diminishes. Additionally, we conducted a detailed investigation into the water conductivity properties of rocks under different stress states using Barton's joint roughness coefficient (JRC) index and rock fractal theory. The roughness features of rock failure surfaces were classified into three categories based on mesoscopic pore and crack undulation forms: straight, wavy, and jagged. We also observed significant confining pressure effects on limestone and sandstone, which exceeding the critical confining pressure led to increased water conductivity in both rocks, albeit through different mechanisms. While sandstone exhibits fissures running across it, limestone shows shear abrasion holes. Beyond the critical confining pressure, the rock failure surface becomes smoother, leading to decreased water flow blocking capacity. The fractal dimension of Ordovician limestone increases significantly under critical confining pressure, leading to a more complex mesoscopic crack extension route.

Analytical solution for mechanical behavior characterization of sandy dolomite tunneling

Analytical solution for mechanical behavior characterization of sandy dolomite tunneling

Mechanical Behavior and Acoustic Emission Characteristics of Cemented Tailings Backfill with Varied Water Loss

Mechanical Behavior and Acoustic Emission Characteristics of Cemented Tailings Backfill with Varied Water Loss

Mechanical behavior and thermal damage characterization of granite after flame jet-water cooling treatment

Flame jet-assisted mechanical rock drilling is expected to solve the hard-rock crushing challenges in underground engineering such as mining, tunneling, and drilling. Therefore, it is important to investigate mechanical behavior of the rock after flame jet-water cooling treatment. In this paper, granite blocks were subjected to flame jet-water cooling treatment, which means the rapid heating of the granite using a flame with a temperature of 1564 °C, followed by water cooling. Then, physico-mechanical behaviors of samples at different distances (all the distances mentioned later mean the vertical distance between the sample axis and the flame jet-water cooling path) were measured. Results showed physico-mechanical parameters of the sample increased as the distance increased. The Vp (P-wave velocity), UCS (uniaxial compressive strength) and BTS (Brazilian tensile strength) of the samples increased from 3171.7 m/s, 84.84 MPa and 5.01 MPa at 0 mm to 3619.3 m/s, 145.86 MPa and 7.30 MPa at 70 mm, respectively. Meanwhile, physico-mechanical parameters of samples at 70 mm all reached more than 95 % of those of untreated samples. As the distance increased, cumulative AE counts at peak stress gradually enhanced, and failure modes of uniaxial samples shifted from shear to tensile splitting failure. The SEM (scanning electron microscope) images illustrated that the closer to the flame jet-water cooling path, the more thermal cracks produced in the sample. Meanwhile, the damage factor can well characterize the thermal damage degree of granite. According to the variation of physico-mechanical parameters and SEM images of samples with distances, it can be assumed that the thermal damage width of granite after flame jet-water cooling was about 140 mm. It was much greater than the 50 mm width of spalling pits, which greatly increased the feasibility of thermal-assisted mechanical rock drilling. The tensile stress induced by the temperature gradient below the spalling pit is the fundamental cause of thermal damage to the rock, which is further aggravated by water cooling. The findings can provide some guidance for flame jet-assisted mechanical rock drilling.

Tribological and mechanical properties of FSW joints of untainted stainless steel and titanium: novel characterization of similar and dissimilar joints

Friction Stir Welding (FSW) is an emerging solid-state welding process that joins dissimilar or similar metals based on requirements. The additional material to make the joint is also a weight reduction factor deemed vital in weight-sensitive industries like aerospace and orthopedic applications. The similar and dissimilar Ti-6Al-3Nb-2Zr-1Mo (Ti6321) and stainless steel (SS 310) joints are performed through friction stir welding. This investigation aims to identify the effect of process parameters on the mechanical behavior and microstructural characteristics of the FSW joints. Five plates are chosen; three are FSW joints, and two are kept in the original base material. In all five plates, tensile, microhardness, and wear tests are performed, including an analysis of grain size. It is observed that the similar Ti6321 joint with a 6 mm pin diameter, 60 mm transverse speed, 900 mm rotational speed, and a constant axial force of 1 KN exhibits a maximum microhardness of 362 HV and a tensile strength of 927 MPa when compared to other joints. The tribological properties are identified as varying load (10–50 N), sliding speed (1–5 m s−1), and a constant sliding distance (1000 m) on pin-on-disc apparatus. It reveals that welding parameters and tool diameter influence tribological characteristics. The surface morphology carried out by FE-SEM revealed that the HAZ is composed of acicular α. The increase in microhardness is higher in WC than in BM due to the uniform distribution of particles. The chemical composition and phases are analyzed using XRD.

Second harmonic generation microscopy, biaxial mechanical tests and fiber dispersion models in human skin biomechanics

Advanced numerical simulations of the mechanical behavior of human skin require thorough calibration of the material’s constitutive models based on experimental ex vivo mechanical tests along with images of tissue microstructure for a variety of biomedical applications. In this work, a total of 14 human healthy skin samples and 4 additional scarred skin samples were experimentally analyzed to gain deep insights into the biomechanics of human skin. In particular, second harmonic generation (SHG) microscopy was used to extract detailed images of the distribution of collagen fibers, which were subsequently processed using a three-dimensional Fourier transform-based method recently proposed by the authors to quantify the distribution of fiber orientations. Mechanical tests under both biaxial and uniaxial loading were performed to calibrate the relevant mechanical parameters of two widely used constitutive models of soft fiber-reinforced biological tissues that account for non-symmetrical fiber dispersion. The calibration of the models allowed us to identify correlations between the mechanical parameters of the constitutive models considered. Statement of significanceConstitutive models for soft collagenous tissues can accurately reproduce the complex nonlinear and anisotropic mechanical behavior of skin. However, a comprehensive analysis of both microstructural and mechanical parameters is still missing for human skin. In this study, these parameters are determined by combining biaxial mechanical tests and SHG stacks of collagen fibers on ex vivo healthy human skin samples. The constitutive parameters are provided for two widely used hyperelastic models and enable accurate characterization of skin mechanical behavior for advanced numerical simulations.