Characterization Of Mechanical Properties Research Articles

Mesoscopic chemical heterogeneities in laser powder bed fused CoCrMo and Ni mixed powders and their effect on the mechanical properties

Microstructural heterogeneity is a feature of common occurrence in alloys additively manufactured using techniques such as laser powder bed fusion (LPBF). Additionally, chemical heterogeneities can arise both at micro- and meso-scales, especially when powder mixtures are used. While such chemical heterogeneities are considered undesirable hitherto, recent studies show that they may be beneficial in tailoring for the desired mechanical property combinations. In this study, we fabricated a graded alloy coupon with the mixed powders of the CoCrMo alloy and elemental Ni and investigated the microstructural and mesoscopic chemical heterogeneities in it. Chemical heterogeneities, which are either rich in Ni or CoCrMo, were observed due to the incomplete mixing of the powders. Banded patterns, with alternating layers that are enriched with different chemical species, were also observed. Distinct stacking fault energies between these chemical heterogeneities result in distinct deformation mechanisms; while planar slip and strain-induced martensitic transformation occur in the CoCrMo-rich heterogeneities, homogenous deformation associated with the wavy slip occurs in the Ni-rich ones. Detailed mechanical property characterizations show that the microscale chemical segregation not only strengthens the matrix but also improves the work hardening ability of the bulk material through kinematic hardening mechanism. These findings substantiate the key design principles for exploiting chemical segregations that form during in situ alloying for simultaneous enhancement of the strength and ductility in AM alloys.

Characterization of mechanical properties of adult chests during pre-hospital manual chest compressions through a simple viscoelastic model

AimThe purpose of this study was to develop a simple viscoelastic model to characterize the mechanical properties of chests during manual chest compressions in pre-hospital cardiopulmonary resuscitation (CPR). MethodsForce and acceleration signals were extracted from CPR monitors used during pre-hospital resuscitation attempts on adult patients. Individual chest compressions were identified and segmented from the chest displacement computed using the force and acceleration. Each compression-recoil cycle was characterized by its elastic coefficient k (a measure of stiffness) and its compression and recoil damping coefficients, dc and dr, respectively (measures of viscosity). We compared the estimated and the calculated chest displacement to assess the goodness of fit of the model. We characterized the chest of patients at the beginning of CPR in relation to sex and age, and their variation as CPR progressed. ResultsA total of 1,156,608 chest compressions from 615 patients were analysed. Mean (95% CI) coefficient of determination R2 for the viscoelastic model was 97.9% (97.8–98.1). At the beginning of CPR, k was 104.9 N⋅cm-1 (102.0–107.8), dc was 2.868 N⋅s⋅cm-1 (2.751–2.984) and dr was 4.889 N⋅s⋅cm-1 (4.648–5.129). Damping during recoil was significantly higher than during compression. Stiffness was lower in women than in men. There were no differences in damping coefficients with sex but a higher dr with increasing age. All model coefficients decreased with compression count, with an overall decrease after 3,000 chest compressions of 34.6%, 48.8% and 37.2%, respectively. ConclusionThe model accurately described adult chest mechanical properties during CPR, highlighting differences between compression and recoil, sex and age, and a progressive reduction in chest stiffness and viscosity along resuscitation. Our findings may merit further investigation into whether patient-tailored and time-sensitive chest compression technique may be appropriate.

DISSECT is a tool to segment and explore cell and tissue mechanics in highly deformed 3D epithelia.

Understanding morphogenesis strongly relies on the characterization of tissue topology and mechanical properties deduced from imaging data. The development of new imaging techniques offers the possibility to go beyond the analysis of mostly flat surfaces and image and analyze complex tissue organization in depth. An important bottleneck in this field is the need to analyze imaging datasets and extract quantifications not only of cell and tissue morphology but also of the cytoskeletal network's organization in an automatized way. Here, we describe a method, called DISSECT, for DisPerSE (Discrete Persistent Structure Extractor)-based Segmentation and Exploration of Cells and Tissues, that offers the opportunity to extract automatically, in strongly deformed epithelia, a precise characterization of the spatial organization of a given cytoskeletal network combined with morphological quantifications in highly remodeled three-dimensional (3D) epithelial tissues. We believe that this method, applied here to Drosophila tissues, will be of general interest in the expanding field of morphogenesis and tissue biomechanics.

Damage constitutive model of uniaxially compressed coal material considering energy dissipation

Coal plays a dominant role in China's energy production and consumption, which also serves as the cornerstone for energy security. The constitutive relationship of coal material is of great significance for the quantitative characterization and evaluation of mechanical properties of isolated coal pillars. From an energy perspective, coal failure is driven by energy, and the energy-based damage characterization provides a basis for the establishment of constitutive model. In this study, since the constitutive model based on the classical Lemaitre's hypothesis shows a significant error in presenting the nonlinear constitutive relationship of coal material, a correction coefficient considering the compaction effect of coal material is first introduced. Then, a novel damage constitutive model that can accurately describe the overall compression state of coal material is constructed. Finally, the theoretical model is compared with exiting models using the experimental data of five types of coal material from different mines. The results show that the evolution of energy dissipation damage variable is highly consistent with that of stress–strain relations. The established constitutive model considering energy dissipation and compaction effect can more accurately describe the nonlinear strength and deformation characteristics of coal material than the classical and existing models. Notably, this new model can be effectively extended to the single cyclic compression conditions to reproduce the loading-unloading-reloading process of coal material.

Temperature dependent tensile fracture strength model of rubber materials based on Mooney-Rivlin model

With the increasingly widespread application of rubber in many fields, the demand for quantitative characterization of temperature dependent mechanical properties in service environments over a wide temperature range is increasing. Tensile fracture strength is one of the most important mechanical properties of rubber materials, but its temperature dependent model without fitting parameters is still rarely reported. In this work, based on Mooney-Rivlin hyperelastic constitutive model, a strain energy expression that explicitly includes tensile fracture strength is derived, and a temperature dependent tensile fracture strength model for rubber materials without fitting parameters is further developed in combination with the Force-Heat Equivalence Energy Density Principle. The prediction results of the model in a wide temperature range are in good agreement with the experimental results. Furthermore, a quantitative analysis of the effect of elastic modulus on tensile fracture strength at different temperatures is conducted. Finally, based on the above conclusions, some useful suggestions on the selection of rubber materials for service in a wide temperature range are proposed.

Mechanical property characterization of mudstone based on nanoindentation technique combined with upscaling method

Mechanical property characterization of mudstone based on nanoindentation technique combined with upscaling method

Rheological and Mechanical Properties of an Acrylic PSA.

The adhesion of pressure-sensitive adhesives (PSAs) is a complex phenomenon that can be understood through the characterization of different properties, including viscoelastic, mechanical, and fracture properties. The aim of the present paper is to determine the viscoelastic behaviour of an acrylic PSA and place it in the viscoelastic window, as well as to determine the tensile strength of the material. Additionally, different numbers of stacked adhesive layers and two crosshead speeds were applied to characterize the tensile strength of the adhesive in the different conditions. Adding a new interface between layers showed a negative influence in the tensile strength, while a higher crosshead speed implied a considerable increase in the same value. Finally, double cantilever beam (DCB) fracture tests were performed, and the J-integral approach was used to evaluate the fracture energy throughout the tests. The substrate roughness, the number of stacked layers, and the thickness of the PSA proved to decrease the performance of the PSA in fracture tests. While tensile bulk tests in viscoelastic materials are not easily found in the literature, as well as DCB tests, for fracture characterization, the obtained results allowed for the characterization of those properties in an acrylic PSA.

Relationship between cardiac mechanical properties and cardiac magnetic resonance imaging at rest in childhood acute lymphoblastic leukemia survivors.

The characterization of cardiac mechanical properties may contribute to better understanding of doxorubicin-induced cardiotoxicity. Our study aims to investigate the relationship between cardiac mechanical properties, T1 and T2 relaxation times and partition coefficient.Fifty childhood acute lymphoblastic leukemia survivors underwent a cardiac magnetic resonance (CMR) at rest on a 3T MRI system and included a standard ECG-gated 3(3)3(3)5 MOLLI sequence for T1 mapping and an ECG-gated T2-prepared TrueFISP sequence for T2 mapping. Partition coefficient, ejection fraction, end-diastolic volume (EDV) and end-systolic volume (ESV) were calculated. CircAdapt model was used to study cardiac mechanical performance (left ventricle stiffness (LVS), contractility (LVC) and pressure (Pmin and Pmax), cardiac work efficiency (CWE) and ventricular arterial coupling).In the whole cohort, our results showed that LVC (R2 = 69.2%, r = 0.83), Pmin (R2 = 62.9%, r = 0.79) and Pmax can be predicted by significant CMR parameters, while T1 (R2 = 23.2%, r = 0.48) and partition coefficient (R2 = 13.8%, r = 0.37) can be predicted by significant cardiac mechanical properties. In SR group LVS (R2 = 94.8%, r = 0.97), LVC (R2 = 93.7%, r = 0.96) and Pmin (R2 = 90.6%, r = 0.95) can be predicted by significant cardiac mechanical properties, while in HR + DEX group CWE (R2 = 49.8%, r = 0.70) can be predicted by significant cardiac mechanical properties. Partition coefficient (R2 = 72.6%, r = 0.85) can be predicted by significant CMR parameters in SR group.Early characterization of cardiac mechanical properties from CMR parameters has the potential to early detect doxorubicin-induced cardiotoxicity.

Application of Ni/SiCw Composite Material in MEMS Microspring.

The microspring is a typical type of device in MEMS devices, with a wide range of application scenarios and demands, among which a popular one is the microelectroformed nickel-based planar microspring prepared by the UV-LIGA technology based on the SU-8 adhesive. It is worth noting that the yield strength of the electrodeposited nickel microstructure is low, and the toughness of the structure is not high, which is unbeneficial for the enduring and stable operation of the spring. The paper mainly presents the methods of preparing high-aspect-ratio Ni/SiCw microstructures for MEMS devices based on UV-LIGA technology, developing Ni/SiCw-based microspring samples with a thickness of 300 μm, and applying a DMA tensile tester for mechanical property tests and characterization. In addition, the paper explores the influence of heat treatment at 300 °C and 600 °C on the tensile properties and microstructure of composite coatings. The results show that the W-form microspring prepared from Ni/SiCw composites not only has a wider linear range (about 1.2 times wider) than that of pure nickel material but also has a stronger resistance capacity to plastic deformation, which is competent for MEMS device applications in environments below 300 °C. The research provides a frame of reference and guidance for improving the stable cyclic operating life of such flat springs.

Dependence of lithium‐ion battery separator porous structure and performance on synchronous bidirectional drawing process regulation of β‐crystal polypropylene

AbstractUneven separator porous construction inevitably raises lithium‐ion migration barriers within the separator and thus limits overall lithium‐ion battery (LIB) performance. In this research, serial LIB separators with various porous constructions were prepared precisely by adjusting the synchronous bidirectional drawing temperatures to confirm the bidirectional drawing mode‐determined porous constructions and subsequent mechanical properties, thermal stability and electrochemical properties of separators. Crystal structure analyses, porous construction diagnoses, mechanical property characterizations and electrochemical tests reveal the competitive relationship between lamella slip and separation during the synchronous bidirectional drawing process. Lamella slip weakens at lower drawing temperatures, enhancing lamella separation and molecular chain rupture within amorphous regions. Therefore, a separator with broken fibrils presents optimized permeability and smoothed ion migration channels, but inferior mechanical properties and thermal stability. Excessive temperature highlights lamella slip, which damages the pore‐forming process, worsens separator permeability and increases ion migration resistance. An appropriate drawing temperature of 100 °C maximally balances lamella slip and separation behaviors, retains intact fibrils and homogenized porous construction, which endows the separator with strengthened mechanical properties, isotropic thermal stability and optimized electrochemical performances. This study provides new insights for synchronous bidirectional drawing in practical separator fabrication and clarifies separator structure‐determined LIB performances. © 2023 Society of Industrial Chemistry.

Atomistic Construction of Silicon Nitride Ceramic Fiber Molecular Model and Investigation of Its Mechanical Properties Based on Molecular Dynamics Simulations.

Molecular simulations are currently receiving significant attention for their ability to offer a microscopic perspective that explains macroscopic phenomena. An essential aspect is the accurate characterization of molecular structural parameters and the development of realistic numerical models. This study investigates the surface morphology and elemental distribution of silicon nitride fibers through TEM and EDS, and SEM and EDS analyses. Utilizing a customized molecular dynamics approach, molecular models of amorphous and multi-interface silicon nitride fibers with complex structures were constructed. Tensile simulations were conducted to explore correlations between performance and molecular structural composition. The results demonstrate successful construction of molecular models with amorphous, amorphous-crystalline interface, and mixed crystalline structures. Mechanical property characterization reveal the following findings: (1) The nonuniform and irregular amorphous structure causes stress concentration and crack formation under applied stress. Increased density enhances material strength but leads to higher crack sensitivity. (2) Incorporating a crystalline reinforcement phase without interfacial crosslinking increases free volume and relative tensile strength, improving toughness and reducing crack susceptibility. (3) Crosslinked interfaces effectively enhance load transfer in transitional regions, strengthening the material's tensile strength, while increased density simultaneously reduces crack propagation.

Characterization of Fine Structure and Mechanical Properties of the Disordered Carbon Materials Synthesized from C60 Fullerite under High Pressure

Characterization of Fine Structure and Mechanical Properties of the Disordered Carbon Materials Synthesized from C60 Fullerite under High Pressure

Squeeze Overcasting of Bimetallic Composite Al2026/Al–4.5%Cu with Acidic Quenching in Aging Treatment: Characterization of Mechanical Properties and Joint Interface Microstructure

Squeeze Overcasting of Bimetallic Composite Al2026/Al–4.5%Cu with Acidic Quenching in Aging Treatment: Characterization of Mechanical Properties and Joint Interface Microstructure

Optical and mechanical properties characterizations of transparent polycrystalline MgAl2O4 spinel

ABSTRACT The microstructure and mechanical properties of polycrystalline spinel ceramics (MgAl2O4) with high translucency were investigated. Several kinds of polycrystalline spinel ceramics were prepared under various sintering conditions, and single-crystal spinel and sapphire were used for comparison. The bending strength of polycrystalline spinel with smaller grain size fabricated without sintering aids exceeded that of single-crystal spinel. The bending strength at 1000°C tended to be lower than that at room temperature. The fracture toughness of polycrystalline spinel prepared without sintering aids measured by SEVNB was higher than that of spinel with sintering aids. By estimation of fracture strength considering different fracture origins, the polycrystalline spinel prepared without sintering aids might be fractured mainly from defects around residual spherical voids. If the size of voids can be minimized in polycrystalline spinel fabricated without sintering aids, both high transmission and good mechanical properties could be achieved.

EVALUATION OF THE MECHANICAL PROPERTIES AND MICROSTRUCTURE OF A-TIG AND TIG WELDMENTS OF INCONEL 617

This work is based on a comparative study of the weldments fabricated by Activated Flux Tungsten Inert Gas (A-TIG) welding and autogenous Tungsten Inert Gas (TIG) welding of 10 mm thick Inconel 617 plates. Flux powders used for A-TIG welding were Titanium dioxide (TiO2) and Silicon dioxide (SiO2). Macrostructure and microstructure analyses and characterization of mechanical properties of both A-TIG and TIG weldments were investigated. The microstructure of Inconel 617 was made up of several secondary phases and fine austenitic grains. Mechanical testing carried out in this study included Bend Test, Tensile Test, Vicker’s Micro-Hardness Test and Charpy Impact Test at room temperature (RT) and a sub-zero temperature (SZT) of −50[Formula: see text]C. The Bend test was found satisfactory for both A-TIG and TIG weldments. TIG weldments’ tensile strength and microhardness were determined to be 782 MPa and 265.44 HV, respectively. However, it was determined that the base metal had a tensile strength of 756 MPa and that the tensile strength and microhardness of the A-TIG weldment were 707 MPa and 252.73 HV, respectively. The TIG weldment was proved to have the highest tensile strength and microhardness due to the availability of strengthening elements like Molybdenum (Mo) and Chromium (Cr), as carbides in the fusion zone. Impact toughness of the A-TIG weldment was higher than that of the TIG weldment both at room and sub-zero temperatures due to the application of TiO2 as flux and the high heat input during A-TIG welding. The ductile mode of fracture was observed in all weldments.

The Characterization of Mechanical and Chemical Properties of Recycled Styrofoam Waste Employing Extrusion Process

<p><em>Styrofoam waste is a polystyrene plastic-based waste in the form of foam with low density. Scavengers or recyclers are not interested in receiving styrofoam waste because of its light density which makes it ineffective in transportation and storage. Styrofoam waste can actually be converted into solid polystyrene products through a thermal-extrusion process but data regarding the optimum operating temperature and the characteristics of the resulting solid polystyrene products are not yet available. The purpose of this study was to investigate the properties of solid polystyrene products resulting from recycled styrofoam waste and determine the optimum temperature of the thermal-extrusion treatment process to be compared with the characteristics of the original polystyrene based on the results of tensile and impact tests. In this study, the processing was carried out using the thermal-extrusion method; Styrofoam is melted and extruded into a mold to produce polystyrene solids. The research was carried out with variations in extrusion temperature at 180°C, 200°C, and 220°C. The polystyrene solids are then molded into tensile and impact test specimens by injection molding. The results showed that the optimal extrusion temperature was 200°C with tensile and impact strength values of 27.55 MPa and 1,069 j/m2, respectively. Compared to the original polystyrene, the tensile strength value is 25.3% lower and the impact strength value is 29.5% lower. The decrease in the tensile and impact strength values is due to the shortening of the molecular bonds in the recycled polystyrene during the thermal-extrusion treatment process. Even though the tensile strength and impact are still lower, the use of styrofoam waste using the thermal-extrusion method has the potential to be developed at the production and commercialization stage because the resulting product has good economic value and can also reduce the use of original polystyrene and at the same time can solve the problem of styrofoam waste.</em></p>

The impact of amplitude modulation frequency in harmonic motion imaging on inclusion characterization.

Ultrasound elasticity imaging techniques aim to provide a non-invasive characterization of tissue mechanical properties to detect pathological changes and monitor disease progression. Harmonic motion imaging (HMI) is an ultrasound-based elasticity imaging technique that utilizes an oscillatory acoustic radiation force to induce localized displacements and estimate relative tissue stiffness. Previous studies have applied a low amplitude modulation (AM) frequency of 25 or 50 Hz in HMI to assess the mechanical properties of different tissue types. In this study, we investigate the dependence of AM frequency in HMI and whether the frequency can be adjusted based on the size and mechanical properties of the underlying medium for enhanced image contrast and inclusion detection. A tissue-mimicking phantom with embedded inclusions at different sizes and stiffnesses was imaged within a range of AM frequencies from 25 to 250 Hz at 25-Hz step size. The AM frequency at which the maximum contrast and CNR are achieved depends on the size and stiffness of the inclusions. A general trend shows that contrast and CNR peak at higher frequencies for smaller inclusions. In addition, for some inclusions with the same size but different stiffnesses, the optimized AM frequency increases with the stiffness of the inclusion. Nevertheless, there is a shift between the frequencies at which the contrast peaks and those with maximum CNR. Finally, in agreement with the phantom findings, imaging an ex-vivo human specimen with a 2.7-cm breast tumor at a range of AM frequencies showed that the highest contrast and CNR are achieved at the AM frequency of 50 Hz. These findings indicate that the AM frequency can be optimized in different applications of HMI, especially in the clinic, for improved detection and characterization of tumors with different geometries and mechanical properties.

Development of a Functional Cementitious Mixture with Expanded Graphite for Automated Spray Construction

Spray-based three-dimensional (3D) concrete printing is an innovative method to automatically construct structures on vertical and overhead surfaces, which contributes to less labor investment and construction time. On the other hand, expanded graphite is widely known for its high thermal and electrical conductivity as a lightweight ingredient, and thus its potential in functional cementitious materials has been gradually realized in recent years. In this study, a lightweight cementitious material containing expanded graphite has been developed specifically for spray-based 3D concrete printing with added values. Through the characterization and overall evaluation of densities, mechanical and rheological properties, and Joule-heating performance, the appropriate expanded graphite content was determined as 1% by weight of cement. Afterward, silica fume was introduced into the matrix to tailor the rheological properties of the mixtures. The subsequent spray-based printing showed that the tailored mixture had significant improvements in the building capacity and spray quality. On the other hand, it also possessed superior Joule-heating performance than the control mixture without expanded graphite. The potential engineering applications of the developed material include deicing and structural health monitoring, and the compatibility with spray-based 3D concrete printing provides extra values of higher construction efficiency and adaptivity to the structures of complex contours.

Characterization of Dynamic Mechanical Properties of Viscoelastic Damper Based on Physics-Constrained Data-Driven Approach

Traditional physics-based mathematical models of viscoelastic (VE) damper often exhibit different degrees of prediction errors under complex working conditions, whereas data-driven approaches have shown significant potential for overcoming such problems, and have not been introduced into any study to describe the dynamic mechanical properties of VE damper. In this paper, the architecture of microsphere model is adopted to represent the spatial distribution of molecular chain structure of VE damping material, which is categorized into free chains and elastic chains. Then, the physics-informed neural network surrogates are introduced to describe the statistical stress–strain behaviors of free chains and elastic chains. Finally, by constructing the physics-constrained loss function based on the combination of physics-based model and data-driven model, a physics-constrained data-driven model is proposed to characterize the dynamic mechanical behaviors of VE damper used for structure vibration control. Based on the existing experimental data, the prediction ability and robustness of the proposed model are comparatively verified, the results reveal that the proposed model can accurately reflect the stiffness and energy dissipation of VE damper under different ambient temperatures, excitation frequencies, and deformation conditions. This study proves the potential of physics-informed neural network theory in characterizing the complex mechanical behaviors of VE damper.

Characterization of mechanical equivalent properties for node enhanced graded lattice structure

Abstract Considering the stress concentration at the rod connection of traditional body-centered cubic (BCC) lattice structure, a node enhanced BCC (NBCC) lattice structure was proposed. In recent years, graded lattice structure has gradually attracted attention due to their unique mechanical properties. In this paper, two different graded NBCC lattice structures were designed and their static mechanical properties were evaluated through quasi-static compression experiments and simulations. Moreover, homogenization theory was applied to calculate the equivalent modulus of lattice structure. This method was extended from uniform lattice structure to graded lattice structure by improving the application of periodic boundary conditions. The obtained results were in good agreement with the experimental and simulation data. The quasi-static compression tests demonstrated that NBCC can effectively reduce the stress concentration and improve the load-bearing capacity about 25% compared to BCC. The graded lattice structures exhibit varying mechanical properties depending on their design and present better mechanical performance in the anisotropic direction. Finally, the relative relationship between the equivalent elastic modulus and the equivalent shear modulus in the lattice structure was studied. The prediction formula for equivalent shear modulus was extended based on the Gibson-Ashby formula.