Dynamic Tensile Strength Research Articles

Anisotropic material removal in ultra-precision grinding of rounded diamond cutting tools

Rounded diamond cutting tools are extensively utilized in ultra-precision cutting applications. However, the anisotropic nature of diamond crystals poses challenges in achieving uniform and controllable material removal using conventional mechanical grinding techniques, impeding further improvements in the precision of diamond tools. This study introduces a novel approach that leverages the diamond dynamic micro tensile strength theory to establish a grinding factor prediction model for any position on the flank face of the tool, considering the combination of R(100)F(100) and R(110)F(100) crystal faces. Experimental investigations are conducted to examine the relationship between the model and the tool's material removal rate. The findings reveal pronounced anisotropy on the flank of the diamond tool during mechanical grinding, and the modified grinding factor model exhibits excellent agreement with the observed change in the material removal rate. These outcomes provide valuable insights for enhancing precision in diamond tool fabrication and advancing ultra-precision cutting techniques.

Simultaneous determination of dynamic fracture toughness and tensile strength through a single three-point bending test

Simultaneous determination of dynamic fracture toughness and tensile strength through a single three-point bending test

Dynamic tensile strength weakening effect of pretension stressed red sandstone under impact load

Dynamic tensile strength weakening effect of pretension stressed red sandstone under impact load

Investigation of the dynamic tensile fracture process of rocks associated with spalling using 3-D FDEM

Understanding the tensile fracturing of rocks under high strain-rate conditions (>20 s−1) is challenging due to experimental constraints. The spalling test has been known as a potential method to measure the tensile dynamic strength in the high strain-rate regime. However to date, the different evaluation methods proposed to interpret the spalling test results yield inconsistent dynamic tensile strength and strain-rate. To understand this inconsistency, a 3-dimensional finite-discrete element method (3-D FDEM), accelerated by general-purpose computing on graphics processing units (GPGPU), is applied to simulate the dynamic tensile fracturing process in the spalling test. The 3-D FDEM simulation results agree with the experimental results in terms of fracture patterns and free surface particle velocity to evaluate the dynamic tensile strength and corresponding strain-rate under various loading rates. The 3-D FDEM simulations can capture the discrepancies in dynamic tensile strength and strain-rate obtained based on the different evaluation methods used in the spalling test. When integrated with experimental analyses, the 3-D FDEM could provide insights, and has potential application in estimating local strain-rate and fracture location, which are key factors for the reliable evaluation of dynamic tensile strength and strain-rate in spalling tests, but are challenging to evaluate by experiments only.

Elucidation of Static Fracture Energy and Dynamic Tensile Performance of Hybrid Steel Fiber-Based Ultrahigh-Performance Concrete

Ultrahigh-performance concrete (UHPC) has great potential for applications in civil and military structures due to its outstanding performance and ability to withstand impact and blast load. This performance can be attributed mainly to the materials and their proportions, especially metallic fibers. Hence, understanding the behavior of UHPC under static and dynamic conditions through the effect of hybridization of steel fibers is essential. Compressive strength and flexural strength were studied in quasi-static mode. In flexural mode, strain characterization was done using a digital image correlation (DIC) technique. Fracture studies were also conducted with notches using a crack mouth opening displacement (CMOD) technique. In high-strain mode, dynamic tensile strength was evaluated using a split Hopkinson pressure bar (SHPB) with a Brazilian disk. Owing to optimized hybridization, enhancement in (1) toughness, (2) energy absorption, (3) crack-resistance capacity, (4) reserve strength, (5) limit of proportionality, (6) fracture energy, (7) stress intensity factor, (8) tensile strain carrying capacity, and (9) dynamic tensile strength were observed. In the process, other findings in relation to fracture, strain rate, and dynamic increase factor were also exemplified. The SHPB dynamic tensile test results, as well as the technical information provided regarding UHPC’s hybrid steel fibers’ strength, failure, and fracture behavior, can be used to improve the design of UHPC building structures to protect against impact and blast attacks.

Direct tensile mechanical properties and damage fracture mechanisms of thermally damaged coal measures sandstone under high strain rate loading

The direct tensile mechanical properties of highly thermally damaged rock under high strain rate loads are a key basic mechanical problem that must be solved for the stability and effective control of surrounding rock stability in the combustion control area of an underground coal gasification project. In this paper, a two-dimensional equivalent grain-based model (GBM) unit and Split Hopkinson Tension Bar (SHTB) numerical model for thermally damaged coal-measures sandstone were constructed using particle flow code (PFC). The comparison with the experimental results shows that the numerical method can accurately describe the dynamic direct tensile behavior of thermally damaged sandstone. The following conclusions are drawn: The dynamic tensile strength of thermally damaged sandstone shows a significant strain rate-strengthening effect. With the increase in thermal damage temperature, the dynamic tensile strength of sandstone increases first and then decreases. The generation and development of hot cracks in a high-temperature environment is the fundamental reason for the change in macroscopic mechanical properties. The dynamic tensile failure process of thermally damaged sandstone can be divided into four stages: the dynamic damage initiation, the dynamic damage development, the damage crack penetration, and the sample dynamic fracture. With the increase in impact velocity, the initial kinetic energy, elastic strain energy, dissipated energy, and elastic strain energy ratio in the failure process of thermally damaged sandstone gradually increase. In contrast, the dissipated energy ratio gradually decreases. As the heat treatment temperature increases, the elastic strain energy and the ratio of elastic strain energy increase first and then decrease.

Experimental Study of Dynamic Tensile Strength of Steel-Fiber-Reinforced Self-Compacting Concrete Using Modified Hopkinson Bar.

As a typical brittle material, the tensile strength of concrete is much lower than its compressive strength. The main failure mode of concrete buildings under explosive and impact loading is spalling, so it is crucial to understand the dynamic tensile performance of concrete. This paper presents an experimental study on the dynamic tensile strength of steel-fiber-reinforced self-compacting concrete (SFRSCC). Specimens of two different self-compacting concrete (SCC) mixes (C40 and C60) and four different fiber volume fractions (0.5%, 1.0%, 1.5%, and 2.0%) are fabricated. Dynamic tensile strengths of SFRSCC are obtained using a modified Hopkinson bar system. The relationships between the dynamic tensile strength of the corresponding SCC mix, the quasi-static compressive strength, and the fiber volume fraction are discussed. An empirical equation is proposed. It is shown that SFRSCC with high compressive strength has higher dynamic tensile strength than low-strength SFRSCC for the same fiber content, and the dynamic tensile strength of SFRSCC possesses an approximately linear relation with the fiber volume fraction. The mechanism underlying this fiber-reinforcement effect is investigated.

An Experiment Study on the Dynamic Behavior of Concrete Used in a Mine Sealing Wall under a High Temperature

Micro-cracks and material deterioration occur in concrete under high-temperature conditions. To reveal the impact resistance of concrete at a high temperature, a dynamic splitting test and dynamic compression test were carried out using a split Hopkinson pressure bar (SHPB). The failure process and dynamic stress–strain curve of the concrete specimens were obtained, investigating the failure mode and dynamic tensile and compressive strength of the concrete. The test results showed that the surface cracks appeared along the loading direction and extended to the core area under the impact load. With an increase in the temperature, different degrees of damage would be caused, the dynamic strength and toughness of the concrete would decrease, showing brittle failure, and the energy absorbed in the failure process would also decrease correspondingly.

Performance evaluation of petroleum hard pitch modified with rice straw bio-oil

In this present study, bio-binder was made using the bio-oil obtained from rice straw and petroleum hard pitch to reduce the air pollution caused by the burning of waste rice straw in the field. The physical, rheological, and chemical tests were conducted on the viscosity-grade binders (VG30 and VG40), petroleum hard pitch, and bio-binders prepared with a blending of petroleum hard pitch with 20 and 30 wt.%. The performance of bituminous mixes made with viscosity-grade binders and bio-binder was evaluated by using the dynamic creep, resilient modulus, and tensile strength tests. The results of the frequency sweep and Fourier transform infrared tests indicate that bio-binders have poor resistance to aging. The rut resistance of the bio-binder modified mix was better than that of the VG30 mix. There is no significant difference in moisture resistance of bituminous mixes prepared with bio-binder and viscosity-grade binders.

A Comparative Study on the Dynamic Tensile Strength Evaluation Method of Rock Materials

The representative calculation methods of dynamic tensile strength applied to the spalling test are comparatively reviewed in the same experimental cases. The results are compared with those of the ISRM suggested dynamic BD method. Through comparative verification results and analysis of methodological characteristics of each determination method in the spalling test, the most reasonable method for calculating dynamic tensile strength in the high strain rate condition is derived. The local strain rate and apparent strain rate are calculated for the same experimental cases, and the difference in the result values according to the strain rate calculation technique is analyzed through comparative verification of the calculated results. Consequently, the characteristics of each dynamic tensile strength determination method and strain rate calculation method in the spalling test are presented, and the results of the review on the most suitable method for calculating the dynamic tensile strength of rock materials are presented.

Experimental Study on Dynamic and Static Tensile Properties of a New Environmental Protection Material

Carbon fiber concrete (CFRC), a late-model environmentally protection material, is formed by mixing chopped carbon fibers into concrete. It can raise static tensile strength and deformation resistance with effect. To further explore the safety of CFRC under dynamic load, this paper studies the factors affecting dynamic and static tensile properties of CFRC by using the SHPB device as an experimental means. The stress rate and chopped carbon fiber content are taken as variables to discuss the difference in tensile strength in the two types of load states. Experiment results show more fiber content in the initial stage can raise the static tensile strength of concrete significantly. However, its increase range has a decreasing trend, while the mixing of excessive carbon fiber reduces its dynamic tensile strength. The dynamic mechanical properties rise by adding stress rate, showing an obvious rate effect. There are significant differences in the influence of carbon fiber on the strength of concrete under two load states. Therefore, the carbon fiber content should be properly selected when designing the concrete mix proportion to satisfy different load states under specific working conditions. This paper provides a reference for the design of new environmental protection materials.

Correction of dynamic Brazilian disc tensile strength of rocks under preloading conditions considering the overload phenomenon and invoking the Griffith criterion

Correction of dynamic Brazilian disc tensile strength of rocks under preloading conditions considering the overload phenomenon and invoking the Griffith criterion

Dynamic enhancing effect of free water on the dynamic tensile properties of mortar

This study investigates free water effect on the dynamic tensile properties of mortar. Fully saturated and saturated-then-redried mortar specimens with two porosities, namely common and high-porosity, are prepared and tested under quasi-static and dynamic split-tension states covering strain rates between 1.49e−06s−1 and 5.29s−1. The split-tensile strength and elastic modulus at different strain rates are quantified. Comparing the dynamic increase factor (DIF) for mortar tensile strength, a maximum difference of 1.2 at strain rate 5 s−1 is found between saturated and dried high-porosity mortars revealing the influence of free water. The testing data is compared with other existing data which shows the mortar water effect is more similar to concrete than limestone and sandstone. The high-speed camera images during the dynamic tests are analysed which revealed a water retarding effect on the dynamic split-tension failure process, resulting in an initial crack delay of up to 0.4 ms due to free water. The wave speed for different mortar specimens at different strain rates is analysed, which shows that higher porosity is more sensitive to the water effect. Possible mechanisms leading to this water effect is discussed. Overall, the study provides a quantitative measure of the water enhancing effect on the dynamic tensile strength of mortar and offers insights into the practical use of water in the design and construction of mortar structures.

Research on impact toughness and crack propagation of basalt fiber reinforced concrete under SHPB splitting test

To cope with accidents such as explosion and high-speed impact, it is necessary to study the dynamic mechanical response of basalt fiber reinforced concrete (BFRC) under impact load. The dynamic splitting test of BFRC was conducted under different impact air pressures by Φ50 mm split Hopkinson pressure bar (SHPB) experimental platform and dynamic DIC acquisition system. The dynamic mechanical characteristics of BFRC under impact load were studied, focusing on analyzing the effects of different basalt fiber (BF) volume rates and average strain rates on its impact toughness. Meanwhile, the process of crack initiation, propagation, and penetration in BFRC during damage and failure was analyzed by DIC technique, the propagation speed and width of tensile crack were calculated by strain nephogram and pixel information. The results show that BFRC with 0.3% fiber content has the highest dynamic splitting tensile strength, dissipated energy and ultimate toughness. The strain rate effect of post-peak toughness is more obvious than that of pre-peak toughness. BF increases the impact toughness of concrete mainly by affecting the post-peak toughness. The crack propagation speed of BFRC is the slowest and the tensile crack width is the smallest with 0.3% fiber content, that is, the appropriate BF content (0.3%) can effectively reduce the damage degree of the matrix under the impact load and has the most obvious effect on the crack resistance and toughening of the matrix.

Dynamic tensile properties of carbon/glass hybrid fibre composites under intermediate strain rates via DIC and SEM technology

Carbon/glass hybrid fibre-reinforced plastic (C/GFRP) can effectively reduce product costs in manufacturing; however, its dynamic tensile properties remain unclear. In this study, the mechanical characteristics of C/GFRP and glass-fibre-reinforced plastic (GFRP) laminates were investigated using an HTM5020 high-speed tensile tester, digital image correlation (DIC), and scanning electron microscopy (SEM) at intermediate strain rates. Six strain rates (1, 10, 100, 250, 500 and 800 s−1) followed by three stacking sequences ([C2,G3,C2]s, [G3,C2,G3]s and [G8]s) were developed. The failure mechanism of C/GFRP under intermediate strain rates was identified using stress–strain curves, DIC sub-images, and macro/micro failure modes. Additionally, the variation laws for fracture strain, elastic modulus, and dynamic tensile strength of C/GFRP were examined. In response to an increase in strain rate, the strength and fracture strain of [C2,G3,C2]s increased by 36.6% and 142.9%. The elastic modulus [G3,C2,G3]s increased by 41.8%. Hybrid laminates are prone to interlaminar failure, resulting in lower strength and higher strain-rate sensitivity. Adding a carbon fibre-reinforced plastic layer effectively improves the stiffness of the laminates. A stiffness prediction formula for C/GFRP is proposed.

Mechanical behavior and failure mechanism of composite layered rocks under dynamic tensile loading

To bolster the safety and efficacy of blasting and impact drilling for underground works in composite rock strata, the dynamic tension of composite rocks requires thorough examination. Given the challenges of composite rock sampling, cement mortars with varying mix ratios are utilized to create composite rock-like test blocks. These blocks are composed of two different strength materials, further processed into differently sized experimental samples as required. Using a split Hopkinson pressure bar (SHPB) test device, we conducted dynamic Brazilian splitting tests at varying incident angles α (the angle between the incident wave direction and the bedding plane) and strain rates on these composite rock-like samples. The modes of crack propagation in some samples were recorded with a high-speed camera. Laboratory tests and PFC2D simulation were used to analyze the dynamic tensile mechanical properties and failure mechanisms of composite rock samples. Findings indicate the dynamic tensile strength of a composite rock sample is governed by the bedding plane inclination angle. As the incident angle rises from 0° to 90°, the dynamic tensile strength of the composite rock sample first decreases, then increases, consistently reaching a minimum value at α = 30°. The damage model of composite rock samples is also influenced by the dip angle of the bedding planes. At α = 0°, the composite rock sample exhibits through-cracks along the incident wave direction and splitting tensile damage is observed. As α increases, the failure mode gradually transitions from splitting tensile damage to a combination of tensile and shear slip damage along the bedding. Tensile damage always manifests in materials of lower strength. When α surpasses 45°, the failure mode reverts from combined damage to splitting tensile damage. Cross-sectional tensile stress clouds generated by PFC software demonstrate that the tensile stress contours at the specimen's center are elliptically distributed, with the ellipse's long axis nearly parallel to the bedding plane.

Dynamic impact and tensile strength characteristics of novel shear thickening fluid (STF)-treated fabric and modeling tensile strength using artificial intelligence

A series of shear thickening fluids (STFs) were prepared based on dispersed fumed silica in virgin polyethylene glycol (V/PEG) and modified PEGs by malonic acid (M/PEG) and tartaric acid (T/PEG). Rheological examination revealed that modification of PEG to a higher chain length of medium molecules remarkably improves STF peak viscosity and decreases the critical shear rate. High-velocity impact resistance of V/STF, M/STF, and T/STF-treated fabric was investigated at different layers and impact velocities and found significant improvement over neat fabric targets. Investigation of the results of two-layer samples showed the energy dissipation of V/STF, M/STF, and T/STF-treated fabrics at an impact velocity of 240 m/s is improved by 30.04%, 40.60%, and 46.06%, compared to the neat fabric, respectively. Furthermore, the tensile strength test revealed that these STFs fill the spaces between the fibers and make the fabric stronger and more resistant to breaking. In addition, a Linear/Nonlinear artificial intelligence regression analysis was performed. The results showed a strong correlation between composite mechanical response and speed. The proposed model can be further used to predict material behavior at other tensile speeds.

Dynamic Tensile Failure Characteristics and Energy Dissipation of Red Sandstone under Dry–Wet Cycles

Studying the dynamic properties of rocks in complex environments is of great significance to the sustainable development of deep-sea metal mineral resource extraction. To investigate the influence of dry–wet cycles on the dynamic tensile properties and energy dissipation of red sandstone, a series of dynamic Brazilian disc tests was carried out through the split Hopkinson pressure bar (SHPB) apparatus. The dynamic tensile behaviors and energy dissipation distribution of the red sandstone specimens after different dry–wet cycles (0, 10, 20, 30 and 40 cycles) were analyzed in this study. The degree of dynamic tensile fragmentation and energy dissipation of red sandstone is significantly affected by the loading rate. Specifically, when the number of dry–wet cycles remains constant, an increase in loading rate results in a significant reduction in the average fragment size, while the energy consumption density exhibits an approximately linear increase. At a fixed loading rate, the energy consumption density decreases approximately linearly with the increase in dry–wet cycles, and the higher the loading rate, the more sensitive the energy consumption density is to the dry–wet cycle. Under a fixed number of dry–wet cycles, the dynamic tensile strength has an exponential relation with the increase in energy consumption density.

Dynamic tensile mechanical properties of thermally damaged sandstone under impact loads and the influence mechanism of composition

The stability of surrounding rock in the combustion void is the key to continuous, safe, and efficient gas production in an underground coal gasification project. The key factors influencing the stability of surrounding rock in the combustion void are high temperature and impact dynamic load. At the same time, rock structure failure mainly depends on the rock materials’ tensile strength. Therefore, it is fundamental to study the dynamic tensile mechanical properties of thermally damaged rocks to control the surrounding rock stability of the combustion void in UCG projects. This paper used the coal measures as the research object. The dynamic direct tensile test of thermally damaged sandstone was carried out using a high-temperature load system and split Hopkinson tension bar (SHTB) test system. The test results showed that the dynamic tensile strength of sandstone increased linearly with the increase in strain rate. In contrast, it increased first and then decreased with temperature. In addition, the nonlinear regression method was applied to establish the prediction model of dynamic tensile properties of thermally damaged sandstone. XRD analyzed the composition and mass fractions of sandstone. From the standpoint of composition change, the change mechanism of the mechanical properties of thermally damaged coal measured in sandstone was illustrated.

Thermo-mechanical performance of nanostructured electrospun composites produced from poly(vinyl alcohol) and cellulosic compounds for potential uses as wound dressings

The purpose of this research was to analyze the morphology, thermal and mechanical properties of poly(vinyl alcohol) (PVA)-based electrospun mats reinforced with cellulose acetate (CA) or cellulose nanocrystalline (CNC) for potential applications in wound dressings. Bead-free and water-stable electrospun nanofibers made of blends of PVA and CA or CNC were successfully produced and crosslinked with glutaraldehyde vapor. Crosslinking slightly increased the nanofibers' diameters in order of 43 and 13% for 80/20 PVA/CA and PVA/CNC electrospun mats, respectively, while maintaining their bead-free morphology. Thermogravimetry (TGA) and differential scanning calorimetry (DSC) evaluations were employed to determine the miscibility and the thermal response of the uncrosslinked and crosslinked mats, reporting a reduction in mass loss upon addition of CA and CNC and upon crosslinking process. Polymers' powder and mats (before and after crosslinking) crystallinity was assessed by X-ray diffraction analysis (XRD). Crosslinked mats experienced a slight reduction in crystallinity compared to the uncrosslinked. Static and dynamic tensile strength tests revealed that CA and CNC doped mats enhanced the Young's modulus and lowered deformation at failure compared to pristine PVA electrospun mats. Data from storage modulus (E′) demonstrated the strength of the physical interactions formed between PVA and the cellulosic derivatives (either before and after crosslinking), highlighting the stiffness of CA (231.58 MPa for the 80/20 mat) and, particularly, CNC (742.04 MPa for the 80/20 mat). This research uncovered important information concerning the chemical and physical relation between polymeric matrices and additives, essential for the proper selection of materials for wound dressings production.