Compressive Failure Stress Research Articles

A failure model for bulk metallic glass based on strain rate-correlated softening mechanism

Due to the amorphous nature of the bulk metallic glasses (BMGs), catastrophic fractures occur once the nucleation and propagation of shear bands occur, which is quite different from crystal materials. So far, the underlying mechanism of BMG failure behavior and its strain rate effect are still controversial. In this work, the quasi-static and dynamic compression experiments of Vit-1 BMG were carried out in a wide range of strain rates from 0.001 s−1 to 5000 s−1. The results show that the variation tendency of failure stress with strain rate can be divided into three stages. The quasi-static failure stress is insensitive to the change of strain rate with only almost constant free volume softening effect inside the material during the failure process. When entering dynamic loading stage, the failure stress decreases significantly, which is caused by a combination of increasing thermal softening and free volume softening effects. When the strain rate increases to the third stage, that is, over 2000 s−1, the failure stress and the softening effects basically remain unchanged. The transformation of failure mechanism is well confirmed by the micromorphology of fracture surfaces. Based on the experimental results, a concise empirical failure model is established, in which the failure stress is decomposed into softening and non-softening parts. The verification experiments show that the model can effectively predict the compression failure stress of BMG under different strain rates.

Suppression of compression induced delamination in tapered laminated composites using a ply scarfing method

Thickness tapering of composite laminates is a common strategy for efficient and lightweight composite structures. The termination of specific plies necessary to achieve such tapering is well known to introduce sites for delamination initiation in laminates. This propensity for delamination is highly dependent on the thickness of the terminated ply, which presents a significant challenge in using thicker materials to improve the production rate of large-scale composite structures.In this work, the effectiveness of ply scarfing in improving the compressive failure stress of tapered laminates made using thick, unidirectional non-crimp fabrics (NCF) was experimentally investigated for the first time. Unidirectional tapered laminates were manufactured using two different NCFs with fibre areal weights of 620 and 1070 g/m2 via resin infusion. Specimens made of the 1070 g/m2 material which incorporated a ply terminated using the ply scarfing method were compared with those including plies terminated using the conventional ply-drop method. which incorporated a ply terminated using the ply scarfing method. The compression failure behaviour of the specimens was analysed using a high-speed camera. The results showed that ply scarfing suppressed delamination of the belt plies under compression and increased the failure stress by ∼60%. Furthermore, the tapered geometry of the terminated ply’s end was effective in preventing the void entrapment at the ply drop and significantly reducing the manufacturing variability.

Effect of loading rate on the compressive behaviour of twill woven carbon/polyamide laminate

This paper presents the experimental investigation on the strain rate effect on the longitudinal compressive behaviour of 2×2 twill woven carbon fibre reinforced polyamide 66. An original easy-to-use specific testing fixture was developed to perform material characterization using an electromechanical machine and a Split Hopkinson Pressure Bar (SHPB) system. The set-up was completed with a high speed camera used to monitor the deformation and failure process and to allow the strain field visualization via Digital Image Correlation (DIC). A particular attention was paid to the validity of the experiments: failure in the test specimen gauge section, stress equilibrium and strain homogeneity. The same testing fixture and specimen geometry were implemented from 1.5×10−5s−1 to 700 s−1. The results comparison shows a positive strain rate effect with a 60% increase in the longitudinal compressive failure stress.

An experimental and computational investigation of embedded wrinkle’s impacts on the compressive responses of thick unidirectional glass fiber-reinforced composites

In thick unidirectional glass fiber-reinforced composites, the out-of-plane embedded wrinkle flaws have a major impact on compressive failure, which should be taken into account and assessed during the design, manufacturing, and inspection phases. The thick unidirectional coupons with embedded wrinkles of various severities were manufactured and tested. The deformation of the wrinkle region was captured by the Digital Image Correlation (DIC). As the wrinkle angle increased, the compressive failure stress decreases and the modulus does not change significantly, while the wrinkle amplitude has a negative effect on both the compressive failure stress and elastic modulus. The linear texture image regression approach is used to account for the path of fibers. The high-fidelity three-dimensional finite element (FE) models considering the real paths of the fibers are established. To reveal the interplay and impact of wrinkle severity parameters on the compressive failure behavior of composites, the progressive damage analyses and cohesive elements are also incorporated. Compared with the experiments, the FE studies accurately identify the dominant failure modes and failure stress values for various wrinkle severity parameters.

Numerical study of rock-breaking mechanism in hard rock with full PDC bit model in compound impact drilling

Geothermal reservoir rocks have the characteristics of high stress, high hardness and high abrasiveness, which makes the drilling rate low and the drilling cost high, and hinders the application of geothermal energy. Improving drilling efficiency in hard rock strata is the prerequisite for large-scale application of geothermal energy. Impact drilling is considered to be the most effective drilling method in hard formations. PDC (Polycrystalline diamond Compact) bit compound impact drilling is one of the impact drilling methods, which has been widely concerned in recent years. In order to further improve the drilling efficiency of this method, the mechanism of PDC bit compound impact rock breaking is studied. Drucker–Prager criterion was used as rock constitutive relation, equivalent plastic strain was used as rock failure criterion, MSE (mechanical special energy) was used as evaluation method of rock-breaking efficiency, and a three-dimensional simulation model of full-size PDC bit for compound impact rock-breaking was built. The rock breaking law in PDC bit compound rock breaking process and the impact vector angle and impact duration on rock breaking efficiency are analyzed. The results show that the compound impact drilling can effectively alleviate the stick–slip vibration phenomenon, and improve drilling efficiency. In the compound impact mode, compressive stress failure and tensile stress failure occur at the same time, and the tensile stress failure is the main failure mode. The peak stress of the rock is 5.49% larger, and the residual plastic deformation is about 4.28% smaller than that of non-impact mode. With the increase of impact angle, the MSE decreases first and then increases a little. The optimal impact vector angle is in the range of 30°–50°. With the increase of the impact time, the MSE decreases in a wavy manner. In the range of 0.2 ms–1.0 ms, the optimal impact time is 0.8 ms–1.0 ms.

INFLUENCE OF HIGH TEMPERATURE TREATMENT ON THE MECHANICAL CHARACTERISTICS OF CARBON-CARBON COMPOSITE MATERIALS WITHPYROCARBON MATRIX

Pyrolytic compaction of porous substrates is one of the methods for obtaining carbon-carbon composite materials. When using such materials at high temperatures, for example, as elements of heaters, it is necessary to take into account the effect of high temperatures on their mechanical characteristics. In this work, the influence of high-temperature treatment on me-chanical characteristics was studied and the mechanism of destruction of samples of the mate-rial "Argolon GR" produced by JSC "Composite" was considered. It is shown that with an in-crease in the processing temperature from 1800 to 2400 °C, the open porosity of the samples increases in proportion to the increase in the number and size of cracks in the samples. The compressive failure stress depends very weakly on temperature, however, the graph of the corresponding dependence clearly shows its slight decrease with an increase in the processing temperature from 2000 to 2400 °C, which corresponds to the accumulation of damage in the material matrix that reduces its strength. Attention is drawn to a significant increase in the ten-sile strength of the material after high-temperature treatment, which is not typical for carbon-carbon composite materials. The dependence of the breaking stress in tension with an increase in the processing temperature for material samples has a pronounced maximum at 2000 °C. The analysis of the change in impact strength, the roughness parameter of the fracture surface of the samples, and the breaking stress in tension showed that the dominant mechanism during fracture is the mechanism of strength increase associated with the violation of the compatibility condition of deformations in the components of the material, while the effect of thermal stress relaxation is very small.

Effects of transversely isotropic layers on failure mechanism of non-homogeny concrete-soil specimens

The mechanism of the failure process and its modes were studied experimentally for transversely isotropic concretes and soils. The two materials, A (concrete) and B (dense soil), were specially prepared for making the layered specimens with a different arrangement of these two materials. The ratio of cement and water in the material A was taken as 4:1 (by weight), respectively. The stiffness and strength of the concrete layers were high compared to that of the dense soil layer (material B). On the other hand a dense layer of soil with low strength and low stiffness was used to represent the material B. Special boxes were built for the preparation of soil-concrete samples. The dimensions of the box were 10 * 10 * 24 cm. Two rectangular spaces were situated on one face. The metallic plates go through these spaces, and a different interface angel was initiated. Concrete and soil layers were formed by pouring the grout and soil into this box. Three different soil volumes have been built, i.e., 25, 50, and 75%. In this research, the laminated concrete specimens with one, two and three soil layers were compared at a constant soil volume. The concrete specimens with transversely isotropic layers of different orientations were examined experimentally and two types of failure were dominant, i.e., the tensile failure at right angles to the layers and the sliding failure parallel to the interfaces of the layers. With a fixed interface angle and fixed concrete volume, the compressive failure stress was increased by increasing the concrete layer. With a fixed layer number and fixed interface angle, the failure stress was increased by increasing the concrete volume. With a fixed layer number and fixed concrete volume, the failure stress has a minimum value when the interface angle is equal to 30°.

MechAnalyze: An Algorithm for Standardization and Automation of Compression Test Analysis.

The mechanical properties of hydrogels, as well as native and engineered tissues are key parameters frequently assessed in biomaterial science and tissue engineering research. However, a lack of standardized methods and user-independent data analysis has impacted the research community for many decades and contributes to poor reproducibility and comparability of datasets, representing a significant issue often neglected in publications. In this study, we provide a software package, MechAnalyze, facilitating the standardized and automated analysis of force-displacement data generated in unconfined compression tests. Using comparative studies of datasets analyzed manually and with MechAnalyze, we demonstrate that the software reliably determines the compressive moduli, failure stress and failure strain of hydrogels, as well as engineered and native tissues, while providing an intuitive user interface that requires minimal user input. MechAnalyze provides a fast and user-independent data analysis method and advances process standardization, reproducibility, and comparability of data for the mechanical characterization of biomaterials as well as native and engineered tissues. Impact statement Mechanical properties of hydrogels are crucial parameters in the development of new materials for tissue engineering. However, manual assessment is tedious, not standardized and suffers under user-to-user bias. Hence, the here presented stand-alone software package provides analysis and statistics of force-displacement and material geometry data to determine the compressive moduli, failure stress, and failure strain in a standardized, robust, and automated fashion. MechAnalyze will substantially support biomechanical testing of hydrogels as well as engineered and native tissues and will thus, be of appreciable value to a broad target group in regenerative medicine, tissue engineering, but also life sciences and biomedicine.

Analysis of scatter in the compression properties of fibre-polymer laminates in fire

Previous research has shown that large scatter can occur in the failure loads and failure times of load-bearing fibre reinforced polymer laminates when exposed to fire. This scatter causes uncertainty in quantifying the structural survivability of composite structures in fire. A combined experimental and modelling study is presented to determine the cause of the scatter and to present a statistical-based model to predict the scatter in the structural survivability of laminates under combined compression loading and one-sided heating by fire. Multiple fire-under-load experimental tests are performed under identical conditions to quantify the magnitude of the scatter for a glass-vinyl ester laminate. The scatter to the deformation rate and time-to-failure of the laminate increased when the heat flux or applied compression load were reduced. A model is presented that can predict the scatter to the compressive failure stress and time-to-failure of a fibreglass laminate when subjected to combined fire exposure and compression loading. The analysis reveals that multiple factors cause the scatter, including small variations in the thickness and fibre content of the laminate.

Temperature dependent mechanical properties of graphene based carbon honeycombs under tension and compression

Graphene-based carbon honeycombs (GCHs) show outstanding physical and mechanical properties, and excellent potential applications. Based on molecular dynamic simulations, we find that temperature plays an important role in the mechanical properties of GCHs. In both the in-plane and out-of-plane cases, the tensile strength and fracture strain of GCHs decrease significantly as temperature increases from 10 to 1800 K. Under compressive deformation, the in-plane compressive stress-strain curves vary slightly when the temperature is lower than 900 K, and change acutely at temperature higher than 1200 K. The out-of-plane compressive failure stress and strain decrease prominently with increasing of temperature from 10 to 1800 K. Our results provide a theoretical guidance for GCHs application in different temperature environment.

An Experimental Study of Dynamic Compression Performance of Self-Compacting Concrete.

To investigate the dynamic performance of self-compacting concrete (SCC), the dynamic uniaxial compression tests at eight different loading strain rates were performed on the ordinary concrete and SCC cubic specimens. Based on the tests, the compression failure patterns and stress–strain curves of both kinds of concrete were obtained. The results show that SCC performs more brittle than ordinary concrete by showing the diagonal crack failure pattern of SCC at a high strain rate. Besides, with the increase of loading strain rate, the peak compressive stress of SCC is slightly lower than that of ordinary concrete, but the increase of elastic modulus is slightly higher than that of ordinary concrete. The peak compressive strains of the two kinds of concrete are discrete under the influence of loading strain rate, thus putting forward the relation equation for the loading strain rate and peak compressive stress increase coefficient of the two kinds of concrete. Besides, based on the theory of elastic–plastic damage and considering the dynamic extension of damage, the dynamic constitutive relation with good applicability between ordinary concrete and SCC was established.

Compression properties of multifunctional composite structures with embedded lithium-ion polymer batteries

Multifunctional light-weight composite structures that combine high load-bearing properties with electrical energy storage capacity have potential application in energy intensive systems such as electric cars. This paper examines the effect of compression loading on the mechanical and electrical responses of light-weight carbon fibre laminates containing embedded lithium ion polymer (LiPo) batteries. The mechanical and electrical responses of the LiPo battery itself to compression loading are also examined. Embedding batteries has a significant adverse effect on the compressive stiffness, failure stress and fatigue life of laminates. The property reductions are attributed to several factors; namely the compressive properties of the battery being much lower than the composite material, the geometric stress concentration created by the battery, discontinuities in the carbon fibres, and the soft polymer layer at the battery-composite interface that effects load transfer. Experimental testing and finite element analysis reveal that the reduction to the compression properties is dependent on the number and arrangement of the batteries.

A numerical study on the influence of composite wrinkle defect geometry on compressive strength

Out-of-plane winkling in continuous-fibre reinforced composites has a significant influence on compressive failure stress, which needs to be considered and evaluated during the design, manufacture and inspection stages, to achieve high-performance composite components. With the development of a three-dimensional characterisation based on non-destructive testing methods and finite-element modelling, it is possible to combine the two techniques to give a prediction of mechanical performance using directly measured geometry. This paper uses a new methodology developed for combining non-destructive characterisation and numerical analysis techniques to automatically create a series of models with controlled wrinkle geometry. It has been possible to determine the dependence of compressive strength on various wrinkle-severity and wrinkle-extent parameters. The outcome shows a dominant dependence on the maximum wrinkle angle in the load direction, with an additional dependence on the wrinkle wavelength for larger wrinkle angles. In terms of the extent of the wrinkled region, the strength reduces as the wrinkle extent in the load direction becomes concentrated locally or the wrinkled proportion of the cross-sectional area (perpendicular to the load) increases.

Mechanical response of fine grained Ti2AlC under extreme thermo-mechanical loading conditions

An experimental investigation was conducted to evaluate the compressive constitutive behavior and fracture initiation toughness of fine grained (∼4.2μm) Ti2AlC in dynamic and quasi-static loading at different temperatures. A Split Hopkinson Pressure Bar (SHPB) apparatus was used in conjunction with an induction coil heating system for dynamic experiments at elevated temperatures, while a universal mechanical testing machine equipped with an extensometer and furnace was used for quasi-static compressive testing. A series of experiments were conducted at different temperatures from 25°C to 1200°C and strain rates of 10−4s−1 and 500s−1. A single edge notched specimen was used to determine the fracture initiation toughness in dynamic and quasi-static loading from ambient temperature to 900°C. The SHPB apparatus was modified for this purpose and high speed photography was incorporated to determine fracture initiation time, and the load corresponding to this time was used to calculate the dynamic fracture toughness. The results of this study reveal that the peak compressive failure stress in dynamic conditions decreases with increasing temperature, from 1600MPa at room temperature to 850MPa at 1200°C. In the dynamic testing condition, the failure remains predominately brittle even at temperatures as high as 1200°C. Under static loading conditions, the peak compressive stresses were always lower than those in dynamic loading conditions, but they also decreased monotonically with increasing temperature. Also under static conditions, a significant drop in peak compressive failure stress and an increase in ductility was observed above the brittle-to-plastic transition temperature of around 900°C. The fracture experiments reveal that the strength and fracture toughness in dynamic conditions are higher than the corresponding quasi-static values by approximately 35% at room temperature and that they both decrease with increasing temperatures. It was found that high temperature and low strain rate promote plastic behavior of Ti2AlC.

The shear fracture toughness, KIIc, of graphite

The critical shear stress intensity factor, KIIc, here-in referred to as the shear fracture toughness, KIIc (MPa√m), of two grades of graphite are reported. The range of specimen volumes was selected to elucidate any specimen size effect, but smaller volume specimen tests were largely unsuccessful, shear failure did not occur between the notches as expected. This was probably due to the specimen geometry causing the shear fracture stress to exceed the compressive failure stress. In subsequent testing the specimen geometry was altered to reduce the compressive footprint and the notches (slits) made deeper to reduce the specimen's ligament length. Additionally, we added the collection of Acoustic Emission (AE) during testing to assist with the identification of the shear fracture load. The means of KIIc from large specimens for PCEA and NBG-18 are 2.26 MPa√m with an SD of 0.37 MPa√m and 2.20 MPa√m with an SD of 0.53 MPa√m, respectively. The value of KIIc for both graphite grades was similar, although the scatter was large. In this work we found the ratio of KIIc/KIc≈1.6.

The Impact Compression Behaviors of Silica Nanoparticles—Epoxy Composites

The compressive properties of epoxy with different silica nanoparticles (SiO2 nanoparticles) contents at quasi-static and high strain rates loading were investigated via experiment. This article evaluates the compressive failure behaviors and modes at different SiO2 nanoparticles contents and different strain rates. The results indicated that the stress strain curves were sensitive to strain rate, and the compressive failure stress of composites with various SiO2 nanoparticles contents increased with the strain rates, and it increased along with SiO2 nanoparticles contents and then declined. The compressive failure stress and the compressive failure modes of the composites were apparently different from the change of SiO2 nanoparticles contents.

2D Model of Strength Parameters for Bamboo Scrimber

Experiments were performed to test the compressive strength of bamboo scrimber board at different grain angle directions. Investigation of test samples allows for the identification of the correlation between compression failure stress and various failure mechanisms at different grain angles. The results of the experiments showed that the density of bamboo scrimber influenced compression failure stress linearly. A new approach to describe the failure stresses of bamboo scrimber was proposed. The density was introduced as a model parameter to describe compressive properties at varying angles of grain. In comparison to a one-dimensional model, there was much less relative error between predicted values and measured values by this 2D model. This report aims to improve the precision of existing strength models for various grain angles and to provide a competing method for the practical use of bamboo scrimber.

Experimental investigation on the compression behaviors of epoxy with carbon nanotube under high strain rates

The compressive properties of epoxy with different carbon nanotubes (CNTs) contents at quasi-static and high strain rates loading had been investigated via experiment to evaluate the compressive failure behaviors and modes at different CNTs contents and different strain rates. The results indicated that the stress train curves were strain rate sensitive, and the compressive stiffness, compressive failure stress of composites with various CNTs contents was increased with the strain rates and CNTs contents. The compressive failure stress and the compressive failure modes of the composites were apparently different as the change of CNTs contents.

Compression behaviors of carbon woven composites with carbon nanotube-filled epoxy resin under high strain rates

The compressive properties and compressive failure mode of multi-layer carbon woven/epoxy resin composites with various carbon nanotube (CNT) contents at quasi-static and high strain rates loading have been investigated in the present paper. The results indicate that the stress–strain curves are strain rate sensitive, and the compressive stiffness and compressive failure stress of composites with various CNT contents are significantly influenced by the strain rates and CNT content. The compressive failure modes of woven composites without CNTs tend to be in shear deformation, delamination fiber breakage and matrix cracking, and the failure modes of woven composites with higher CNT contents are mainly delamination, matrix cracking and shear deformation.

Effect of high through-thickness compressive stress on fibre direction tensile strength of carbon/epoxy composite laminates

The fibre-direction tensile strength of carbon/epoxy laminates under the influence of through-thickness compressive stresses has been experimentally investigated. In a unidirectional (UD) laminate, the through-thickness compressive stresses will cause premature longitudinal fibre-splitting, masking the effect of transverse stresses on the fibre-direction strength. Here a cross-ply laminate has been used. With the addition of 90° plies preventing the 0° fibres from splitting, it effectively allows the dependence of fibre-direction tensile strength on high through-thickness stresses to be studied. The severity of the through-thickness loads has been varied using cylindrical indenters of different radii, up to the loads near the through-thickness compressive failure stress of the cross-ply laminate. The results show that there is a linear decrease in fibre-direction strength with the mean through-thickness stress. In all the test cases, the specimens failed in a catastrophic brittle manner, with scanning electron micrography showing primarily a fibre tensile fracture mode. The detailed stress state in the specimens has been calculated via finite element analysis. Two failure criteria are proposed, which can be used as conservative design criteria concerning fibre-dominated failures in multiaxial load scenarios.