Micro-scale Testing Research Articles

Study on high-temperature emission behaviors of crumb rubber modified asphalt: Experimental analysis and molecular simulation approach

The harmful emissions produced during the manufacturing and construction processes of crumb rubber modified asphalt (CRMA) significantly hinder its widespread application. Addressing this issue hinges on a thorough investigation into the mechanism governing its high-temperature emissions. This study employed microscale testing methods to analyze the microstructure and chemical property disparities between CRMA and base asphalt (BA). Subsequently, the impacts of varying crumb rubber (CR) content, experimental temperature, and sulfur stabilizer dosage on the high-temperature emissions of CRMA were investigated. Furthermore, comparative analyses of the molecular weight distribution, emission species, and CR crosslink density in asphalt after the fume experiment were conducted to further elucidate the high-temperature emission mechanisms. Finally, molecular simulation techniques were employed to analyze the interactions between CR and the four fraction molecules of asphalt at the microscale. The results indicated that the fume release volume of CRMA initially decreased and then increased with the addition of CR, while both the experimental temperature and sulfur stabilizer content exhibited a positive correlation with emission volume. CR reduced the volatilization of some small molecular hydrocarbons in the BA by absorbing light fractions. Meanwhile, excessive swelling caused the crosslinking density of CR to decrease by 77 %, which led to the release of toxic substances. At 20% CR content, the overall emissions of CRMA achieve their lowest level; however, the emission of toxic gases does not diminish. Molecular simulations have also confirmed the above results, showing that there is a strong interaction between CR and the light fractions. Compared with asphaltene molecules, rubber molecules had higher molecular polarity and stronger adsorption behavior for light fraction molecules.

Utilization of red mud in high-performance grouting material for semi-flexible pavement

The huge amount of red mud has brought great challenges to the sustainability of global economic development. Red mud, a solid waste, causes resource wastage and environmental pollution, even endangering human health. A technology used to overcome such a situation involves broad-scale recycling of red mud in road engineering. In this study, Bayer red mud is utilized as a high-performance grouting material for semi-flexible pavement (SFP). A series of sensitivity analyses are performed using macroscale testing to determine the optimal amount of red mud and water-cement ratio for red mud-based cementitious materials (RCM) grouting material. This includes alkali-activated “red mud-slag powder” binary cementitious material (RSCM) and non-alkali-activated “red mud-cement” cementitious material (RCCM). Additionally, the hydration process and products of RCM are analyzed using microscale testing, including scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). The results of the analysis indicate that red mud has significant potential for recycling as SFP materials to achieve the goal of high fluidity and early strength. The workability and early strength of RCCM are even higher than those of cement, indicating that part of the cement can be replaced by red mud. Moreover, the macroscale conclusions of RCM can be confirmed by microscale testing. These low-carbon grouting materials offer the added advantages of recycling waste that would otherwise be destined for landfill, along with reducing the carbon footprint and economic impact associated with cement production.

Impact of pre-soaked lime water carbonized recycled fine aggregate on mechanical properties and pore structure of 3D printed mortar

Compared to natural fine aggregate, recycled fine aggregate has disadvantages such as high water absorption and poor strength. Accelerated carbonization is considered a method to enhance recycled aggregate performance. However, the lack of substances available for carbonation reaction in old cement mortar restricts the enhancement of RFA performance. In this study, a pre-soaked lime-water carbonization method was employed to enhance carbonization efficiency and improve cement mortar performance by introducing additional sources of calcium. Therefore, the focus was on investigating the effects of pre-soaked lime-water carbonization-treated recycled fine aggregate with different replacement ratios (0%, 30%, 50%, 70%, 100%) on the mechanical properties of 3D printed mortar. In addition, combining XRD、SEM-EDS, and X-CT microscale testing methods, the study analyzed the influence of carbonized recycled fine aggregate on the pore structure of 3D printed recycled mortar. The purpose was to reveal the reinforcement mechanism of pre-soaked lime water composite carbonization. Experimental results showed that the pre-soaked lime water carbonization method improved the physical properties of recycled fine aggregate, with the most significant decrease in the water absorption ratio, which decreased by 53.89%. Incorporating appropriate carbonized recycled fine aggregate can enhance the mechanical properties of 3D printed mortar, increase interlayer bonding strength, reduce mechanical anisotropy and overall porosity, and improve pore defects. Defects on the aggregate surface are filled with CaCO3 carbonization products, improving the pore structure and strengthening the interfacial transition zone, thus enhancing the resistance of 3D printed recycled mortar to external forces. The findings of the present work not only improve the utilization of recycled sand but also provide methods and ideas for improving the properties of 3D printed recycled mortar.

Comparative Analysis and Error Assessment of Nanoindentation Evaluation Techniques for NafionTM117

AbstractAdvances in the application of polymers for electrochemical cells require an understanding of their viscous deformation mechanisms and their interaction with moisture. Nanoindentation offers a localized, microscale testing alternative to traditional tensile testing. However, the viscoelastic nature of the polymers, combined with their increased compliance, presents challenges in the analysis of nanoindentation results. In addition, the dependence on moisture results in significant scatter and low repeatability. This study combines nanoindentation and tensile testing as a verification method and compares different correction protocols for static nanoindentation to investigate the mechanical behavior of polymer electrolyte membranes. Comparisons of different indentation devices, analysis methods, and indentation protocols show a significant overestimation of Young’s modulus using the classical Oliver–Pharr method compared to values determined from tensile tests. Nanoindentation at different humidity levels revealed different mechanisms leading to a decrease in Young’s modulus and hardness with increasing humidity.

Comparison of macroscale and microscale mechanical properties of fresh and fixed-frozen porcine colonic tissue

Mechanical changes to the microenvironment of the extracellular matrix (ECM) in tissue have been hypothesised to elicit a pathogenic response in the surrounding cells. Hence, 3D scaffolds are a popular method of studying cellular behaviour under conditions that mimic in vivo microenvironment. To create a 3D biomimetic scaffold that captures the in vivo ECM microenvironment a robust mechanical characterisation of the whole ECM at the microscale is necessary. This study examined the multiscale methods of characterising the ECM microenvironment using porcine colon tissue. To facilitate fresh tissue microscale mechanical characterisation, a protocol for sectioning fresh, unfixed, soft biological tissue was developed. Four experiments examined both the microscale and macroscale mechanics of both fresh (Fr) and fixed-frozen (FF) porcine colonic tissue using microindentation for microscale testing and uniaxial compression testing for macroscale testing. The results obtained in this study show a significant difference in elastic modulus between Fr and FF tissue at both the macroscale and microscale. There was an order of magnitude difference between the Fr and FF tissue at the microscale between each of the three layers of the colon tested i.e. the muscularis propria (MP), the submucosa (SM) and the mucosa (M). Macroscale testing cannot capture these regional differences. The findings in this study suggest that the most appropriate method for mechanically characterising the ECM is fresh microscale mechanical microindentation. These methods can be used on a range of biological tissues to create 3D biomimetic scaffolds that are more representative of the in vivo ECM, allowing for a more in-depth characterisation of the disease process.

A triple-source CT system for micro-scale investigation of geological materials: A simulation study

A triple-source CT system is proposed for micro-scale testing of geological materials. This study aims at reducing the projection acquisition time by two-thirds compared to a conventional single-source CT system. The proposed system with different positioning errors in the source-to-object distance (SOD) was simulated and tested using the Shepp-Logan phantom model, as well as slices of sand, glass beads, and concrete samples. Furthermore, the imaging quality of a single-source and the triple-source CT system with different dead detector pixels was compared. The results showed that within the maximum allowable positioning error, the pixel differences between the simulated and the original images are close to zero, and the structural similarities are greater than 0.96. In the presence of dead detector pixels, the quality of the simulated images in the triple-source CT system is superior to that of a single-source CT system. The presented triple-source CT system performs well in high-quality image reconstruction.

Analysis of local characteristics and microstructure of dissimilar metal interface in scrubbing refill friction stir spot welding joint

Friction stir spot welding (FSSW) is one of the solid-state welding methods and dissimilar material joining by FSSW has been investigated. ‘Scrubbing refill FSSW (Sc-RFSSW)’ has developed as a new dissimilar material joining method, and it was shown that Sc-RFSSW provides higher joint strength than conventional FSSW methods in joining the aluminum alloy and non-coated steel. In this study, the microscale testing was performed to evaluate the dissimilar material interfacial strength of Sc-RFSSW joints. The relationship between the interfacial strength distribution and the macroscopic strength of the Sc-RFSSW joint was analyzed. In addition, the microstructure of the dissimilar material interface was observed, and the relationship between the microstructure and the interface strength was shown.

Identification of changes in mechanical properties of sandstone subjected to high temperature: meso-and micro-scale testing and analysis

Material properties largely depend on their structure, and are strongly dependent on the scale of observation. Under the influence of various processes, the structure of a material can undergo evolution, which leads to major changes in the mechanical parameters and morphology of the medium. To understand the behaviour of a given material exposed to the influence of various factors, e.g. loading and temperature treatment, and to be able to modify it appropriately, it is crucial to recognize its structure both in the scale of engineering applications and at the micro-scale. The article proposes a procedure for assessing changes in the structure of sandstone exposed to the temperature treatment. The presented procedure allows the morphology of the material to be evaluated and the influence of temperature treatment on mechanical parameters of rocks to be analysed, by combining use of different laboratory techniques. The changes in rock material have been characterized using three investigative techniques, i.e. a uniaxial compression test, nanoindentation and micro-computed tomography. The uniaxial compression tests were carried out for 11 different temperature values in the range of 23–1000 °C, which enabled the determination of the change in uniaxial compressive strength and Young’s modulus of the sandstone as a function of temperature. Micro-scale laboratory tests were utilised to identify changes in the mechanical and morphological parameters of the sandstone exposed to the temperature of 1000 °C. The results were referred to those obtained for the reference samples, i.e. not subjected to heating (T = 23 °C). Comparison of the results showed an evident relation between the microstructure changes and the mesoscopic properties.

A New Modeling Framework for Multi-Scale Simulation of Hydraulic Fracturing and Production from Unconventional Reservoirs

This paper describes a new modeling framework for microscopic to reservoir-scale simulations of hydraulic fracturing and production. The approach builds upon a fusion of two existing high-performance simulators for reservoir-scale behavior: the GEOS code for hydromechanical evolution during stimulation and the TOUGH+ code for multi-phase flow during production. The reservoir-scale simulations are informed by experimental and modeling studies at the laboratory scale to incorporate important micro-scale mechanical processes and chemical reactions occurring within the fractures, the shale matrix, and at the fracture-fluid interfaces. These processes include, among others, changes in stimulated fracture permeability as a result of proppant behavior rearrangement or embedment, or mineral scale precipitation within pores and microfractures, at µm to cm scales. In our new modeling framework, such micro-scale testing and modeling provides upscaled hydromechanical parameters for the reservoir scale models. We are currently testing the new modeling framework using field data and core samples from the Hydraulic Fracturing Field Test (HFTS), a recent field-based joint research experiment with intense monitoring of hydraulic fracturing and shale production in the Wolfcamp Formation in the Permian Basin (USA). Below, we present our approach coupling the reservoir simulators GEOS and TOUGH+ informed by upscaled parameters from micro-scale experiments and modeling. We provide a brief overview of the HFTS and the available field data, and then discuss the ongoing application of our new workflow to the HFTS data set.

Crack velocity measurements through continuous stiffness monitoring of cyclically loaded notched micro-beams of thin graded Pt–Ni-Al bond coats

The notched clamped beam geometry has proven to be a useful geometry in evaluating local mechanical properties like fracture and fatigue of thin graded platinum nickel aluminide bond coats. Cyclic fatigue tests performed on different zones of these coatings have shown that the structural stiffness of the beam is a useful parameter in estimating localized damage in front of the notch root, which can arise either due to cyclic softening from micro-crack nucleation and propagation in the crack wake or due to work hardening in the plastic zone surrounding the crack tip. This paper describes the use of finite element method-based analysis to quantify different geometrical factors that affect cyclic stiffness data in the micro-beam bending methodology employed in the present study. Variations in the stiffness values measured at the beginning of each loading cycle can occur due to factors such as the effect of loading line offsets (both lateral and angular) and the notch length to width ratio (a/W). Using this analysis, it was found out that lateral offsets affect the starting stiffness of the beam more profoundly compared to angular offsets. It has also been shown that for beams having lengths of $$\sim $$ $$80-90\,\upmu \mathrm{m}$$ and an a/W ratio of $$\sim $$ 0.3–0.4, the starting stiffness variations can be kept under 10%. The stiffness can also be used to estimate crack velocities (da/dN) in an approximate sense using the finite element method. Detailed finite element analysis has been performed to estimate through thickness crack lengths from cyclic stiffness drops. The applied stress intensity factor for real crack geometries observed during testing have been computed using the extended finite element methodology and da/dN vs $$\Delta $$ K plots have been generated for two cases. This paper highlights the importance of using computational analysis in optimizing and augmenting micro-scale fatigue testing data and thus providing for a richer dataset through such analysis.

Microscale testing and modelling for damage tolerant composite materials and structures

There is a need for damage tolerant composite material for very large engineering structures such as wind turbine rotor blades. The development of improved composite materials with higher damage tolerance will be most efficiently guided by models of the relevant damage modes. Two damage modes are considered in the present paper: Fatigue damage due to in-plane tensile stresses in the fibre direction and cyclic delamination crack growth from a ply drop. For both failure modes the damage evolution is considered at macro- and microscale. Micromechanical models are used to illustrate how changes in the mechanical properties of fibre, matrix and the fibre/matrix interface can lead to an increased damage tolerance material. Also, micromechanical testing methods for characterizing the relevant micromechanical parameters are discussed.

Crystal Strengths at Micro- and Nano-Scale Dimensions

Higher strength levels, achieved for dimensionally-smaller micro- and nano-scale materials or material components, such as MEMS devices, are an important enabler of a broad range of present-day engineering devices and structures. Beyond such applications, there is an important effort to understand the dislocation mechanics basis for obtaining such improved strength properties. Four particular examples related to these issues are described in the present report: (1) a compilation of nano-indentation hardness measurements made on silicon crystals spanning nano- to micro-scale testing; (2) stress–strain measurements made on iron and steel materials at micro- to nano-crystal (grain size) dimensions; (3) assessment of small dislocation pile-ups relating to Griffith-type fracture stress vs. crack-size calculations for cleavage fracturing of α-iron; and (4) description of thermally-dependent strain rate sensitivities for grain size strengthening and weakening for macro- to micro- to nano-polycrystalline copper and nickel materials.

Failure of fracture toughness criterion at small scales

Fracture toughness testing at small scales is widely adopted for materials of limited size. Recent experimental results demonstrate that the fracture toughness of single-crystal tungsten decreases by half as the specimen size drops equally from the order of several dozen micrometers to 1 $\ensuremath{\mu}\mathrm{m}$. To explore this size-dependent fracture feature, we construct a fracture model by combining the Griffith strength theory and elastic-damage law. It is shown that as the specimen scales down to a critical size, the fracture behavior changes from the fracture toughness domination to the strength domination, leading to a seeming decrease of the fracture toughness. Reviewing mechanical fracture testing of different brittle materials at small scales, we found that their fracture is dominated by fracture strength instead of fracture toughness, which explains why the reported values of fracture toughness obtained from the microscale testing are significantly less than the corresponding ones measured at the macroscale. Our study has profound guiding significance for the characterization of the fracture toughness at small scales.

Mechanically tunable coaxial electrospun models of YAP/TAZ mechanoresponse and IGF-1R activation in osteosarcoma

Current in vitro methods for assessing cancer biology and therapeutic response rely heavily on monolayer cell culture on hard, plastic surfaces that do not recapitulate essential elements of the tumor microenvironment. While a host of tumor models exist, most are not engineered to control the physical properties of the microenvironment and thus may not reflect the effects of mechanotransduction on tumor biology. Utilizing coaxial electrospinning, we developed three-dimensional (3D) tumor models with tunable mechanical properties in order to elucidate the effects of substrate stiffness and tissue architecture in osteosarcoma. Mechanical properties of coaxial electrospun meshes were characterized with a series of macroscale testing with uniaxial tensile testing and microscale testing utilizing atomic force microscopy on single fibers. Calculated moduli in our models ranged over three orders of magnitude in both macroscale and microscale testing. Osteosarcoma cells responded to decreasing substrate stiffness in 3D environments by increasing nuclear localization of Hippo pathway effectors, YAP and TAZ, while downregulating total YAP. Additionally, a downregulation of the IGF-1R/mTOR axis, the target of recent clinical trials in sarcoma, was observed in 3D models and heralded increased resistance to combination chemotherapy and IGF-1R/mTOR targeted agents compared to monolayer controls. In this study, we highlight the necessity of incorporating mechanical cues in cancer biology investigation and the complexity in mechanotransduction as a confluence of stiffness and culture architecture. Our models provide a versatile, mechanically variable substrate on which to study the effects of physical cues on the pathogenesis of tumors. Statement of significanceThe tumor microenvironment plays a critical role in cancer pathogenesis. In this work, we engineered 3D, mechanically tunable, coaxial electrospun environments to determine the roles of the mechanical environment on osteosarcoma cell phenotype, morphology, and therapeutic response. We characterize the effects of varying macroscale and microscale stiffnesses in 3D environments on the localization and expression of the mechanoresponsive proteins, YAP and TAZ, and evaluate IGF-1R/mTOR pathway activation, a target of recent clinical trials in sarcoma. Increased nuclear YAP/TAZ was observed as stiffness in 3D was decreased. Downregulation of the IGF-1R/mTOR cascade in all 3D environments was observed. Our study highlights the complexity of mechanotransduction in 3D culture and represents a step towards controlling microenvironmental elements in in vitro cancer investigations.

Advanced microelectromechanical systems-based nanomechanical testing: Beyond stress and strain measurements

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Microscale shear specimens for evaluating the shear deformation in single-crystal and nanocrystalline Cu and at Cu–Si interfaces

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On the Planarization Mechanism and Pad Aging Effects of Soft Pad Polishing: A Perspective From the Micro-Mechanical Properties of Soft Pads

The local viscoelastic properties of soft polishing pads with different usage durations are measured by a micro-scale mechanical analysis testing platform. The testing reveals stimulus-adaptive local viscoelasticity of soft pads under the activation of asperity contact. This phenomenon suggests asperity-dependent local modulus. Such an increase of local modulus induced by higher asperity provides a further enhancement effect to the planarization of surface asperity. Furthermore, the measurement outcomes suggest that the reaction of local micro-scale viscoelastic properties of the soft pad surface to the workpiece asperity will decay with usage time. The current study provides a detailed understanding of the aging effects for the soft pad and explains the performance decay during soft pad polishing from a local micro-scale interfacial perspective.

Response of stone wool–insulated building barriers under severe heating exposures

This article presents the experimental results of stone wool–layered sandwich constructions, with either steel or gypsum claddings, tested under four different heating exposures: 7 kW/m2 incident radiant heat flux exposure, 60 kW/m2 incident radiant heat flux exposure, parametric time–temperature curve exposure and ISO 834 standard time–temperature exposure. The test apparatus used were a movable radiant panel system, a mid-scale furnace (1.5 m3) and a large-scale furnace (15 m3). The results show that reduced-scale tests are capable of reproducing the heat transferred through the construction at large scale provided there is limited mechanical degradation. The results indicate that the availability of oxygen is fundamental to the fire behaviour of the sandwich composites tested. Reactions occurring in stone wool micro-scale testing, such as oxidative combustion of the binder or crystallisation of the fibres, have a limited effect on the temperature increase when wool is protected from air entrainment.

Estimation of anisotropic properties of nano-structured arrays by modal vibration control at microscale

ABSTRACTNano-structured arrays are engineered to meet the requirements of a variety of applications such as microfilters, sensors, and structural interface due to their unique mechanical characteristics, which cannot be achieved by conventional solid materials. However, it is hard to evaluate the elastic properties of nano-structured arrays owing to the discrete structure, sample size, and availability of suitable techniques. To facilitate this, we develop an advanced three-dimensional microscale vibration testing process. In the test, a specially designed three-dimensional microspecimen with tuned mass is excited by a piezoelectric actuator, and the resonance frequencies are detected by a laser device successfully. The anisotropic elastic moduli of nano-structured array composed of helical nano-springs are identified from a single spectrum. This array shows so strong characteristic anisotropy that the solid one hardly can attain. The microscale testing technique can be extended to other materials and microstructures.

Microscale Testing and Modelling of Cement Paste as Basis for Multi-Scale Modelling.

This work aims to provide a method for numerically and experimentally investigating the fracture mechanism of cement paste at the microscale. For this purpose, a new procedure was proposed to prepare micro cement paste cubes (100 × 100 × 100 µm3) and beams with a square cross section of 400 × 400 µm2. By loading the cubes to failure with a Berkovich indenter, the global mechanical properties of cement paste were obtained with the aid of a nano-indenter. Simultaneously the 3D images of cement paste with a resolution of 2 µm3/voxel were generated by applying X-ray microcomputed tomography to a micro beam. After image segmentation, a cubic volume with the same size as the experimental tested specimen was extracted from the segmented images and used as input in the lattice model to simulate the fracture process of this heterogeneous microstructure under indenter loading. The input parameters for lattice elements are local mechanical properties of different phases. These properties were calibrated from experimental measured load displacement diagrams and failure modes in which the same boundary condition as in simulation were applied. Finally, the modified lattice model was applied to predict the global performance of this microcube under uniaxial tension. The simulated Young’s modulus agrees well with the experimental data. With the method presented in this paper the framework for fitting and validation of the modelling at microscale was created, which forms a basis for multi-scale analysis of concrete.