Dynamic Tensile Tests Research Articles

Fracture Mode and Thermal Damage Evolution of Sandstone Under the Coupling Effect of Thermal Treatment and Impact Load

The dynamic properties of high-temperature sandstone quickly deteriorate with different cooling methods, which leads to the instability of underground engineering rock structures. Therefore, it is of great significance to quantify the changes in the dynamic characteristics of high-temperature cooled sandstone under impact loads. Therefore, the sandstone is heated to different temperatures and cooled using three methods. A dynamic tensile test is performed using the Splitting Hopkinson Pressure Bar (SHPB) test set for high-temperature cooled sandstone. At the same time, the transient process of rock failure was examined using high-speed cameras. The influence of different temperatures and cooling methods on the thermal damage value of sandstone was analyzed, and the prediction equation was formed. The change in rock energy during rock failure under impact load was calculated.

Optimizing mechanical properties and pioneering biodegradable polymer blends for superior energy-absorbing structures used in sport helmets

Replacing elements made of conventional plastics (like polystyrene) with biodegradable substitutes is part of the trend of sustainable development and waste reduction. The manuscript covers issues related to the design, manufacturing and testing of sports helmet protective inserts made of biodegradable material. The FEM numerical simulations carried out by the authors allowed to determine the optimal desirable mechanical properties (Re = 8.5–65 MPa, E = 500–8000 MPa for 30 × 30 mm inserts; Re = 10.5–60 MPa, E = 500–7500 MPa for 48 × 48 mm inserts; Re = 13–95 MPa, E = 400–8500 MPa for 55 × 55 mm inserts) and geometric parameters (wall thickness equal to 0.2–0.5 mm, height of 20 mm), ensuring the formation of a plastic fold, which is the most effective energy-absorbing mechanism. The conducted quasi-static compression, bending and dynamic tensile strength tests allowed to determine blends with appropriate proportions of durable PLA with more plastic PBAT, PBS and TPS that meet the established criteria: PLA50PBAT50, PLA30PBAT70 and PLA30TPS70.

Coupling effects of loading rate and temperature on mode I dynamic fracture characteristics of ductile cast iron

Engineering structures made of ductile cast iron (DCI) have a potential risk of failure due to extreme service environments such as high velocity impacts and sub-zero temperatures. Therefore, it is of great importance to investigate the dynamic fracture behavior of DCI under the coupling effect of rate and temperature. In this paper, two sets of impact velocities (5 m/s and 13.5 m/s), and four sets of temperatures (20 °C, −40 °C, −60 °C, and −80 °C) were specially designed to investigate the coupling effect on the mode I dynamic fracture toughness (DFT). The results show that DFT is positively correlated with impact velocity at 20 °C, −40 °C and −60 °C. However, at −80 °C, the rate effect is reversed. Moreover, DFT decreases with decreasing temperature regardless of impact velocity. With microscopic analysis, the phenomenon of ductile–brittle transition (DBT) was observed in the failure of the material, and it’s verified by dynamic tensile tests. The ductile–brittle transition temperature (DBTT) of DCI is determined as −39.7 °C by comparing the DFT with the strain energy density (SED) characterization method.

Dynamic tensile behaviors and crack propagation in fiber-reinforced cementitious composites: Experimental investigation and Peridynamic simulation

Fiber-Reinforced Cementitious Composites (FRCC) have gained significant attention in engineering applications due to their superior mechanical properties and toughness, particularly under high strain rate conditions. This study performed dynamic tensile tests on FRCC at high strain rates (35-110 s⁻¹) using a Split Hopkinson Tensile Bar (SHTB) apparatus. Additionally, a novel Peridynamic (PD) model was developed for the SHTB and FRCC system, leveraging the advanced capabilities of the emerging PD theory. The study compared and analyzed dynamic tensile strength, ultimate tensile strain, strain rate effects, failure modes, and crack development in FRCC with different fiber ratios at various high strain rates, using both experimental data and PD simulations. The results show that the PD-SHTB-FRCC dynamic model developed in this study exhibits high consistency between numerical simulations and experimental findings, effectively capturing the processes of crack initiation, propagation, and complete failure in FRCC specimens. The dynamic tensile properties of FRCC improve significantly with increased strain rates, with polyethylene (PE) fibers providing superior reinforcement compared to steel fibers. Notably, the dynamic tensile strength, peak tensile stress, and ultimate tensile strain of FRCC increase significantly with rising strain rates, with specimens containing higher PE fiber content showing a more pronounced enhancement effect. For strain rates between 42.6 s⁻¹ and 76.1 s⁻¹, considering dynamic tensile strength, ultimate tensile strain, and peak tensile stress, the optimal combination for resisting dynamic tensile loads was 1.5% PE fibers and 0.5% steel fibers. At a strain rate of 99.8 s⁻¹, a 2% PE fiber ratio alone provided the best performance.

Effect of High Fiber Content on Properties and Performance of CFRTP Composites

Continuously reinforced thermoplastic composites are widely used in structural applications due to their toughness, light weight, and shorter process cycle. Moreover, they provide flexibility in design and material selection. Unlike thermoset composites, continuous fiber content to maximize mechanical properties in thermoplastic composites has not been well investigated. In this paper, three thermoplastic systems are investigated to study the optimum content of continuous fiber reinforcement. These systems include carbon fiber/polyphenylene sulfide (PPS), glass fiber/PPS, and glass fiber/high-density polyethylene (HDPE). Tapes were made at several fiber contents, and samples were compression molded and tested using thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile, 3-point flexure, and short-beam shear tests. Results revealed that higher fiber content led to an increase in the glass transition and melt transition temperatures of the polymer. Some mechanical properties increased with fiber content and then began to decrease upon further addition of fibers, while other properties, such as ductility and interfacial bond strength, decreased with more reinforcement. Furthermore, the optimum fiber contents to maximize mechanical properties are different for different properties and different materials.

A novel rigidizable inflatable lunar habitation system: design concept and material characterization

Constructing lunar bases is crucial as lunar missions progress towards utilization and exploitation. The challenging lunar environment, with its unique characteristics and limited resources, requires special materials, structures, and construction methods. Inflatable structures offer great potential for lunar construction due to their advantages in transportation, stowage, construction, and reliability. This paper proposes a rigidizable inflatable lunar habitat that maintains its shape even after air leakage, enhancing safety, durability, and fixability. The membrane material adapts to different requirements during transportation, construction, and service, achieved through solid-state actuation of shape memory polymer (SMP) for stiffness variation, allowing multiple moves and ground tests. This work comprises three parts: 1) system: design concept and construction processes, 2) material: design and characterization of restraint and rigidization materials, and 3) structure: numerical validation of structure properties. Finite element analysis, based on material models obtained through dynamic mechanical analysis (DMA) and tensile tests, demonstrates the effectiveness of including an SMP rigidization layer in preventing collapse and enhancing dynamic properties. This paper not only proposes a new system, but also provides material design methods and requirements, along with structural validation techniques. Findings validate the feasibility of rigidizable inflatable lunar habitats, applicable in extreme environments, also in temporary buildings, space structures, and soft robotics.

Synergic effects of silica aerogel (SA) particles on tensile behavior of cryo-conditioned epoxy: The role of particle morphology and mixing sequence

Cryogenic conditions are of crucial importance for gas storage tanks to provide increased storage density, reduced pressure requirements and minimized energy losses. Incorporation of silica aerogel (SA) particles as a nanostructured material with extremely low density and exceptional thermal insulating properties into epoxy matrices has the potential to facilitate the progress of high performance nanocomposite coatings for advanced cryogenic applications. The objective of this study is therefore to investigate the impacts of particle size, particle content, milling method and mixing sequence on toughness of the cryo-conditioned epoxy coatings. SA particles of varying size (50 μm to 300 μm) were prepared using two different techniques (planetary ball milling vs. 2-blade grinding). Nanocomposite samples were prepared using two distinct mixing sequences, i.e., adding particles (in 0, 0.5, 1 and 1.5%wt.) to epoxy followed by mixing with hardener or adding particles to epoxy/hardener (with 3 or 15 min delay). The nanocomposite samples were subjected to different cryogenic conditions (single 3-h immersion in liquid nitrogen vs. three consecutive 1-h immersions). Mechanical properties of the samples were evaluated by conducting fractography, dynamic mechanical thermal analysis (DMTA) and tensile tests. Large SA particles settled towards the bottom of nanocomposite and resulted in loss of mechanical properties at cryo-conditions. Mixing 1 wt% of optimized SA particles with epoxy/hardener system led to an enhanced tensile strength (26 %), stiffness (3 %) and toughness (71 %) by providing uniform cross-linking reactions and mitigating thermal shock effects at cryo-conditions. Toughening mechanisms included crack deflection, crack pinning, crack arrest and crack branching.

Bridging the gap between rate-dependent plasticity and stress wave dynamics: Calibrating a constitutive model for high-strength steel by inverse optimization

We present an approach for quantifying the flow stress of metals under dynamic loads, based on experiments that involve distinct but related physical phenomena. In modified Taylor tests, a stress-wave generated velocity–time signal is measured, which indirectly provides information on the plastic deformation behavior of the tested material at high strain rate. The Johnson–Cook plasticity model is calibrated for a high-strength steel on the basis of such measurements in combination with quasi-static and dynamic tensile test data. The plasticity model parameters are found with differential evolution through the inverse optimization of material test simulations. A consistent set of model parameters is identified that reproduces measurements from all types of tests. The obtained plasticity model features a small initial yield stress, which is compensated by large strain hardening so as to produce a realistic engineering yield stress. An independent calibration method is employed, by regression of the model on quasi-static and dynamic tensile test results, that confirms the validity of the plasticity model parameter values.

The influence of high strain rates on mechanical properties and microstructure of CuCrZr alloy under strong current carrying condition

The extreme condition of high-speed metal deformation under intense current flow is commonly encountered in the realms of national defense, military, and industry. However, there has always been a lack of effective research method for the micro deformation mechanism of metal under this extreme condition. We have developed a high current and high strain rate tensile (HCHST) testing platform based on RC circuits, which is used to research the micro-deformation mechanisms of CuCrZr alloy under this extreme condition. The dynamic tensile tests of CuCrZr alloy at different high strain rates (1401s−1, 2957 s−1, 5503 s−1, 8012 s−1) under the high current density (6550 A/mm2) condition were conducted using the HCHST experimental platform. The mechanical properties and microstructure of CuCrZr alloy under the HCHST were analyzed by combining TEM and EBSD. The research results indicate that the microhardness of the alloy in the HCHST #1 environment (6550 A/mm2,1401s−1) is almost the same as the original state. This is attributed to the strong current promoting the movement of dislocations and reducing the accumulation of dislocations. Under condition like HCHST#1, the dislocation annihilation rate and dislocation formation rate of CuCrZr alloy almost reach equilibrium. At higher strain rates, the dislocation multiplication rate is much higher than the dislocation annihilation rate caused by strong current. This imbalance leads to dislocation entanglement and the formation of dislocation cells, resulting in an increase in the microhardness of the material. Additionally, EBSD was used to analyze the changes in grain size, average volume fraction of LAGBs, average KAM value, and texture of the samples, further verifying the dislocation evolution and microhardness changes of copper alloys under HCHST conditions. Our research results provide strong theoretical for the application of CuCrZr in the field of electrical thermal mechanical coupling.

Research on the static and dynamic tensile damage mechanism of concrete based on fuzzy sets

The quantitative analysis of microscopic damage mechanisms in concrete and the formulation of damage evolution equations using mathematical theory and computerized tomography (CT) imaging are still emerging fields. The test data from CT scans have yet to be fully exploited. This study proposes a method for quantitatively characterizing mesoscale damage evolution in concrete. By segmenting CT images from static and dynamic tensile tests, we define metrics such as the aggregate rate, mortar rate, and porosity to examine the damage progression under both stress conditions. We then establish a damage evolution model based on porosity changes. Our findings reveal that crack growth in concrete is slower under static tension, with cracks navigating around aggregates towards weaker regions. Conversely, under dynamic loads, cracks propagate more rapidly and directly through aggregates, following paths of quicker energy dispersion. Static loading results in less aggregate damage than does dynamic loading, with a notable increase in porosity and a more varied change in the mortar rate. The damage to the finer components of concrete increases as the crack-adjacent region diminishes. Damage is generally more extensive under static loading than under dynamic loading. The proposed porosity-based damage evolution model effectively describes concrete damage under static tension, leveraging CT technology to enhance the universality of the research and offering a microscopic-level theoretical foundation for studying concrete mechanical properties.

Reconsidering Museums’ Climate and Seasonal Adjustment for Vulnerable Artifacts

ABSTRACT The paper provides new experimental evidence for vulnerable artifacts on the dependence of failure strain on the loading rate corresponding to typical environmental loads lasting between hours and months. Animal glue-based ground was chosen for this study as an easily available, hygroscopic and brittle material as well as due to its abundance in collections and its relevance when discussing the risk of mechanical damage to objects. Gesso specimens were tested using dynamic mechanical analysis and tensile testing at different frequencies, under a variety of loading rates and temperatures. The time-temperature superposition principle was used to predict the material response to slow deformations (lasting hours to months) that are otherwise inaccessible on laboratory timescales. The results demonstrate that brittle materials such as animal glue-based grounds do not benefit from longer cycles of applied loads as failure strain is not time-dependent within the investigated timescale.

Rate-Dependent Tensile Properties of Aluminum-Hydroxide-Enhanced Ethylene Propylene Diene Monomer Coatings for Solid Rocket Motors.

Quasi-static and dynamic tensile tests on aluminum-hydroxide-enhanced ethylene propylene diene monomer (EPDM) coatings were conducted using a universal testing machine and a Split Hopkinson Tension Bar (SHTB) over a strain rate range of 10-3 to 103 s-1. This comprehensive study explored the tensile performance of enhanced EPDM coatings in solid rocket motors. The results demonstrated a significant impact of strain rate on the mechanical properties of EPDM coatings. To capture the hyperelastic and viscoelastic characteristics of EPDM coatings at large strains, the Ogden hyperelastic model was used to replace the standard elastic component to develop an enhanced Zhu-Wang-Tang (ZWT) nonlinear viscoelastic constitutive model. The model parameters were fitted using a particle swarm optimization (PSO) algorithm. The improved constitutive model's predictions closely matched the experimental data, accurately capturing stress-strain responses and inflection points. It effectively predicts the tensile behavior of aluminum-hydroxide-enhanced EPDM coatings within a 20% strain range and a wide strain rate range.

Correlation between AFM characterizations and dynamic mechanical testing to assess the ductile-to-brittle transition during ABS photodegradation

The extensive use of Acrylonitrile Butadiene Styrene (ABS) raises challenges due to its vulnerability to oxidative degradation, primarily impacting its mechanical behavior. Photodegradation appears to be the pivotal driver in this degradation process. The main aim of the present study is to provide a comprehensive approach to the underlying mechanisms governing the transition from ductile to brittle behavior in ABS after exposure to UV-induced photodegradation. This study thus focuses on the multiphase nature of ABS, wherein polybutadiene (PB) nodules are dispersed within a matrix of styrene-acrylonitrile. Dynamic mechanical tensile tests have been employed to highlight aged layer mechanical impact by blocking the dissipative response of the matrix and applying a homogenous stress field, while atomic force microscopy (AFM) has been used to characterize the local mechanical properties of ABS finely. The evolution of global mechanical properties has been correlated with changes in microstructural behavior. One of the main contributions of the present work is the correlation between the formation of brittle layers with the brittle state of aged ABS. Mechanical testing using dynamical tensile test revealed a critical aging time marking the transition from a ductile to a brittle state of the 450 µm thick samples. Chemical analysis using infrared spectroscopy revealed evolutions in the material composition, especially in the carbonyl, hydroxyl, and PB unsaturation groups. Distinct thin oxidized layers on each exposed surface were observed using optical microscopy. Finally, AFM analysis on the exposed surface shows the stiffening of PB nodules, indicating the formation of brittle thin layers due to oxidation causing an apparent fragile behavior of ABS.

Extension of Flow Behaviour and Damage Models for Cast Iron Alloys with Strain Rate Effect

Cast iron alloys with low production cost and quite good mechanical properties are widely used in the automotive industry. To study the mechanical behavior of a typical ductile cast iron (GJS-450) with nodular graphite, uni-axial quasi-static and dynamic tensile tests at strain rates of 10−4, 1, 10, 100, and 250 s−1 were carried out. In order to investigate the influence of stress state on the deformation and fracture parameters, specimens with various geometries were used in the experiments. Stress strain curves and fracture strains of the GJS-450 alloy in the strain rate range of 10−4 to 250 s−1 were obtained. A strain rate-dependent plastic flow model was proposed to describe the mechanical behavior in the corresponding strain-rate range. The available damage model was extended to take the strain rate into account and calibrated based on the analysis of local fracture strains. Simulations with the proposed plastic flow model and the damage model were conducted to observe the deformation and fracture process. The results show that the strain rate has obviously nonlinear effects on the yield stress and fracture strain of GJS-450 alloys. The predictions with the proposed plastic flow and damage models at various strain rates agree well with the experimental results, which illustrates that the rate-dependent plastic flow and damage models can be used to describe the mechanical behavior of cast iron alloys at elevated strain rates. The proposed plastic flow and damage models can be used to describe the deformation and fracture analysis of materials with similar properties.

Material Testing for Physicists: Unraveling the Dissipative Nature of Silicone Elastomers via Ball Drop Testing

AbstractIsaac Newton once contemplated the fall of an apple, setting in motion a revolution in the understanding of gravity. In a similar spirit of curiosity and inquiry, here a journey is embarked upon to explore the intricate world of viscoelastic damping for polydimethylsiloxanes (PDMS). Inspired by the notion that even the simplest of phenomena can yield profound insights, a novel approach to study damping in silicone elastomers through a simple ball drop test is introduced. This novel solution allowes for precise measuring and analyzing the material's damping characteristics under various conditions. By carefully controlling the release and monitoring, the response of the falling ball by simple video tracking, valuable insights into the key viscoelastic properties of silicone blends are extracted, including rebound resilience, Young's modulus, and complex modulus. Through the analysis of trajectory data generated during the sphere's interaction with the silicone damper, dynamic and static material parameters are determined. Remarkably, these outcomes closely align with results obtained from cost‐intensive and high‐maintenance industrial measurement setups such as dynamic thermomechanical analysis (DTMA) or tensile testing. This approach not only simplifies the complexity of the system but also offers a cost‐effective and efficient means of gaining essential knowledge in material science.

Experimental and simulation study on quasi-static and dynamic fracture toughness of 2A12-T4 aluminum alloy using CTS specimen

Based on the study of dynamic fracture toughness of mixed mode I/II fracture crack, using compact tensile shear (CTS) specimen and the method of split Hopkinson tensile bar (SHTB) combined with special fixture, which complete the experiments of complex fracture modes of 2A12-T4 aluminum alloy material under quasi-static and dynamic tensile tests. By combining the results of finite element simulation with experimental–numerical method, the feasibility of Richard’s theory formula in dynamic fracture experiment is discussed. The variation law of fracture toughness under quasi-static and dynamic complex fracture under mixed-mode was analyzed by finite element simulation and experiment. The results show that, in the process of quasi-static and dynamic fracture, the fracture toughness of CTS specimen under mixed mode I/II crack loading is the highest. The conclusion is proved by Richard theorical formula and experimental–numerical methods jointly. When the specimen is subjected to pure mode I fracture, the quasi-static fracture toughness is consistent with that is in condition of dynamic experiment. However, when the specimen is subjected to mode II and mixed mode I/II fracture, the dynamic fracture toughness changes greatly compared with the quasi-static fracture toughness. In addition, in the dynamic fracture experiment, the dynamic fracture toughness of mixed mode I/II depends on the initiation time, and the quasi-static fracture criterion is no longer applicable.

Experimental and constitutive model investigation on the tensile mechanical properties of polyurea at wide strain-rate range

Polyurea is extensively utilized as a protective coating material for structures under impact and blast loadings, owing to its significant large tensile deformation capability and strain hardening effect. In this study, the tensile performance of polyurea was experimentally and theoretically investigated. Firstly, rational geometric shapes and dimensions were designed, and a series of quasi-static and dynamic uniaxial tensile tests were conducted to obtain the nonlinear stress-strain curves at different strain rates. The results indicated a notable strain-rate effect in polyurea, with an increase in elastic modulus and tensile stress as the strain rate increased. Moreover, as the strain rate escalates, the strain hardening effect becomes more pronounced, thereby enhancing the protective capabilities of polyurea. Subsequently, an existing hyperelastic model, namely the Mooney-Rivlin (MR) model, was modified to incorporate the strain rate effect, resulting in a non-linear visco-hyperelastic constitutive model. Furthermore, the proposed constitutive model and parameters were validated by simulating existing tensile and blast tests using the finite element (FE) program LS-DYNA. This work could provide a reference for the design of structural protection.

Dynamic tensile characteristics of elliptically shaped Ni8Ti9Cr1 rings

Thin-walled tubes with elliptically shaped annular sections are widely applied in fuel ducts and exhaust pipes. However, the tensile mechanical properties of these structures have remained elusive due to the lack of accurate testing methods. This study aims to fill this gap by establishing circumferential tensile testing methods for static and dynamic conditions by employing a split Hopkinson tensile bar and an electronic universal tensile machine. The quasistatic and dynamic tensile characteristics of two distinct elliptically shaped Ni8Ti9Cr1 rings with different aspect ratios were investigated at room temperature, revealing a significant loading rate effect. The tensile curves exhibited considerable fluctuations, which diminshed as aspect ratios decreased. These fluctuations were attributed to stress waves propagating back and forth between the specimen, the clamp, and the bars, causing superimposition. The Johnson‒Cook (JC) model was established based on the experimental results and then incorporated into the finite element model to gain deep insights into the mechanical responses of the Ni8Ti9Cr1 rings under tension. Our findings reveal that dynamic tensile testing of elliptically shaped Ni8Ti9Cr1 rings induces a complex stress state, which leads to nonuniform necking effects and structural vibrations, revealing complex behaviors previously unexplored. This investigation significantly advances the understanding of quasistatic and dynamic tensile responses in elliptically shaped ring structures, shedding light on their mechanical intricacies across varying conditions.

Biaxial tensile behavior of CoCrFeNi high-entropy alloy under dynamic and proportional loadings

The dynamic failure behavior of CoCrFeNi High-Entropy Alloy (HEA) under plane biaxial stress was investigated in detail. The dynamic biaxial tensile tests were conducted using an Electromagnetic Biaxial Split Hopkinson Tensile Bar (EBSHTB) system. For comparison, the quasi-static uniaxial and biaxial tensile tests, as well as dynamic uniaxial tensile tests, were performed respectively. A cruciform specimen suitable for large plastic deformation was designed and employed in the experiments. The Finite Element Method (FEM) verified that the improved cruciform specimen could satisfy the basic requirements. The feasibility of the proposed specimen was further confirmed through loading tests. Finally, the quasi-static and dynamic yield loci of the HEA in the first quadrant of the principal stress space were plotted. The results indicate that the alloy exhibits obvious strain hardening effect and strain rate strengthening effect, the yield locus and plastic work contours can be accurately described by Hill’48 criterion.

Dynamic tensile behaviour of 7A04-T6 aluminium alloy at elevated temperatures

As typical light engineering metals, aluminium alloys are widely employed in modern manufacturing and construction sectors. Among them, 7A04-T6 high-strength aluminium alloy (AA7A04-T6), alloying with Zn, Mg and Cu and manufactured via the T6 temper process, is a good alternative to steel in construction and is now attractive to engineers and researchers. The structural members made from 7A04-T6 High-strength aluminium alloy are also vulnerable to a variety of accidental actions, such as impact and blast which expose the AA7A04-T6 material to both high strain rates and elevated temperature. To date, investigations into the mechanical properties of AA7A04-T6 material under the loading conditions with strain rates and temperatures coupled are still limited. Dynamic tensile tests were conducted under the rate-temperature coupling test conditions in this work, to study the influence of strain rate and temperature on the stress-strain response of AA7A04-T6 material. The ranges of the test strain rate and temperature were from 0.001 s−1 to 102 s−1 and from 20 ℃ to 200 ℃, respectively. Based on the classical Johnson-Cook model and Cowper-Symonds model, a modified model was proposed for AA7A04-T6 material and good agreement is achieved in the comparison between the predictions and the measured stress-strain curves, which could facilitate the relevant fine analysis and resilient design in the future.