Revealing the microscopic fragmentation mechanisms under higher strain rate is of great significance for investigations of collision of tiny space debris and finer granulation of pills. However, it’s difficult for current experimental methods to conduct impact loading on micro-particle and investigate complicated failure mechanisms. This study aims to develop a novel impact testing system for micro-particles, using glass spheres in diameter of 0.3 mm and 0.4 mm as examples. The electromagnetic launched system was designed to keep good flight attitude for small striker, avoiding influences of vibration and friction. The Photonic Doppler Velocimetry (PDV) system was designed to measure wave information caused by extremely tiny local fractures. The system was proved to successfully capture the transient response of local ruptures. The coupling tensile-shear failures were decoupled by a self-similarity-based approach, and the eigen-strengths of micro-glass were obtained. This study provides a powerful device to test tiny particles, afford ultra-high strain rate loading and could provide profound understanding of dynamic breakage due to heterogeneity in material.
The luminescent intensity ratio (LIR) method of measuring temperature with thermographic phosphors has long been reported to exhibit sensitivities to experimental geometry as a test article moves in 3D space. This work aims to evaluate the sensitivity of combined thermographic phosphor digital image correlation (TP+DIC) to experimental geometry and test article motion. In doing so, two novel geometry compensated formulations of LIR are derived that ensure consistent phosphor emission volume is measured in both cameras and compared against the traditional LIR methods. Full-field uncertainty quantification techniques were applied to compare traditional LIR methods to the novel LIR methods as the phosphor moved throughout a measurement volume representative of a thermomechanical experiment. Three experiments were performed: (Experiment A) systematic rotation at room temperature to evaluate the angular emission profile of the phosphor coating, (Experiment B) systematic translation where temperature calibrations were taken at each fixed location in space, and (Experiment C) compound translation/rotation at two steady-state temperatures. Experiment A showed that the phosphor coating was non-Lambertian, and compensation was achieved using the viewing angle measured from DIC. Experiment B showed that while mean filtered traditional LIR measurements may yield accurate temperature measurements at a single position in space, they often suffer from significant bias during material motion that can be reduced by 3x by moving to geometry compensated LIR techniques. Finally, Experiment C confirmed that applying mean filters to traditional LIR methods causes significant over-confidence in the measurement and showed that the temperature calibration of the non-Lambertian geometry compensated LIR method remained reliable at all positions within the working volume. Through all three experiments, it is shown that the geometry compensated, non-Lambertian (GCNL) method remains consistently aligned with the temperature calibration. Therefore, the new GCNL LIR method presented herein can be applied to complex thermomechanical experiments while using the prediction interval from the temperature calibration as a reasonable full-field uncertainty estimate throughout deformation.
Deep-hole drilling is the method of choice for measuring residual stress profiles through the thickness of large metallic specimens. The procedure involves measuring the change in internal diameter that occurs within a reference hole drilled into a material when the surrounding material is overcored. The residual stress at each depth within the reference hole is typically calculated assuming that it depends only on the diameter change at that depth, without any influence from any adjacent material. This approach is generally effective, but it has only modest ability to identify any local features within the residual stress profile. This study seeks to identify the geometrical characteristics that control spatial resolution of local features in a measured residual stress profile and to develop an effective analytical method for revealing those features. A finite element model was created to account for the interactions between the material at each hole depth and the adjacent material. The results were analyzed to identify the character of the measurement method. Example calculations showed that the overcore inner diameter is the major influence on the spatial resolution of stresses. The proposed stress computation is shown to be effective in providing greater ability to resolve local residual stress details. An approximate calibration method is presented that allows stress calculations to be done without need for finite element calculations. A compact computation method is presented that significantly improves the spatial resolution of local features within the residual stress profile evaluated from deep-hole drilling measurements.
For MEMS resonant devices, lower internal friction is essential for energy-efficient operation and stable resonance, but how sputtering conditions tune damping in thin-film metallic glasses (TFMGs) is still unclear. This work aims to elucidate how magnetron sputtering deposition power influences the internal friction and underlying free volume in Zr-Cu-Ti TFMGs, to advance experimental mechanics understanding of damping in amorphous thin films. Zr–Cu–Ti TFMGs were deposited on micromachined silicon paddle-cantilevers from 75 to 150 W. Film structure and properties were characterized by grazing-incidence XRD, EDS, and nanoindentation, while internal friction was extracted from ring-down signals measured by laser Doppler vibrometry using logarithmic decrement and a bilayer-beam model to isolate film loss. Increasing sputtering power increased deposition rate and caused measurable composition changes, reduced elastic modulus by 20
Selective diffusion of different types of particles is desirable in multiple modern chemical and biological technologies. However, distinguishing the transport of particles with similar physical, chemical, or geometrical properties is challenging because their transport behavior is governed by nearly identical thermodynamic and kinetic conditions within the host medium. Existing efforts to achieve the selective diffusion of particles include size filtration by the mesh of polymeric networks or by specific chemical interactions through dynamic bonds. However, these approaches rely on pronounced differences in particle size or affinity. This study aims to explore ultrasound excitation as an engineering space to enhance nanoparticle selectivity through dynamic control of mechano-diffusion in polymer networks. We developed an ultrasound diffusion characterization platform (UDCP) to systematically observe and analyze the diffusion behavior of particles. By leveraging a model particle-hydrogel system and the ultrasound excitation, we generated tunable acoustic fields that impose cyclic mechanical perturbations on the polymer network and the embedded particles. Through the UDCP, we characterized the diffusion of various molecules with different sizes under various stretches of the hydrogel media and different ultrasonic power levels. For the individual kind of particles, the low- and intermediate-power ultrasonic stimulations can enhance the diffusion across all sizes, while the high-power ultrasound can induce a non-monotonic trend of diffusion profile due to polymer network damage. For two types of particles, ultrasonic stimulation can enable strong particle diffusion selectivity under moderate power levels. Ultrasound stimulations amplify the particle diffusion selectivity in a non-invasive approach, which can be utilized as an ideal method to achieve the selective diffusion of broad classes of particles, forming universal applications of ultrasound in drug delivery, chemical remediation, and in-situ biosensing.
Intracranial aneurysms arise from the progressive deterioration of the biomechanical integrity of arterial walls. Currently, there is no available method that can predict the risk of aneurysm wall rupture based on a quantitative analysis of its mechanical characteristics. This work forms part of a broader research project aimed at developing a personalised tool to support clinicians. This tool will help improve the management of unruptured intracranial aneurysms through knowledge of the in vivo mechanical properties of patients’ aneurysmal tissue. In line with this objective, an original arterial wall deformation device was designed and tested using a non-destructive experimental method on polymer-based arterial phantoms. In parallel, a numerical model was developed to complement the experimental study and to deepen the understanding of the interaction between the deformation device and the aneurysm wall. An initial assessment, carried out using a simplified numerical model and compared with experimental results, has already been conducted. The current objective is to increase the biofidelity of the model and to further evaluate this framework. The deformation prescribed on the polymer phantom arteries by the device was measured using Digital Image Correlation. The fluid–structure interaction between the device, the fluids and the arterial wall was simulated using the Finite Element Method. The model was made more realistic through the use of a geometrically biofidelic artery, a fluid reproducing blood viscosity, and hyperelastic parameters for the vascular wall properties. The evaluation process involved extracting and interpolating the numerical results, and then comparing the computed strain and stress fields with the experimental measurements. The strain fields obtained from the linear elastic and hyperelastic models were compared with experimental data for validation. Analysis of the stress fields, however, revealed that the hyperelastic model allowed a more accurate validation of the numerical model. The maximum error associated with the maximum stress reaches 27.7
Traditional creep testing takes thousands of hours and incurs large costs. Calibrating constitutive models for creep offers the potential to perform shorter tests and extrapolate to longer durations. This work focuses on the design of a complex specimen geometry, suitable for a Materials Testing 2.0 (MT2) style creep test, that uses a heterogeneous stress field and inverse identification to determine constitutive model parameters. A digital toolchain comprising of finite element simulation, image deformation, 2D Digital Image Correlation (DIC) and inverse identification has been used to assess candidate geometries. The open source material modelling code New Engineering Material model Library 2 (NEML2) has been used to create a GPU-accelerated Virtual Fields Method (VFM) for inverse identification. Promising specimen geometries have been identified from a grid search of a simple two variable geometry parameterisation. Investigations of the design space suggest that wide stress ranges and high constitutive model parameter sensitivities drive accurate creep constitutive model identification. However, the maximum achievable stress range and sensitivity is limited by the ability of the DIC system to resolve the strain field. The results demonstrate the necessity of including DIC within the design loop for MT2 tests to generate realistic and measurable specimen designs.
Redistribution Cu interconnect is a key enabler for heterogeneous integration of chiplets for high-performance computing. Objective: The high-density integration of dissimilar materials in the chiplet package significantly increases stress and the risk of failure. It is therefore critical to understand the inelastic behavior of the Cu interconnect to accurately assess stress and damage accumulation. To evaluate Cu behavior under realistic dimensions and boundary conditions, this study conducted tensile tests on a redistribution interconnect strip specimen with parallel micron-scale Cu traces encapsulated in polyimide (PI) dielectric, rather than a single Cu line or thin film. Results: The experimental results showed that the yield stress of the Cu trace is higher than that of its bulk form. Additionally, the Cu trace exhibits strong rate-dependent inelastic behavior before fracture. The time- and temperature-dependent inelastic behavior of the micron-scale Cu traces was considered by using the Anand viscoplastic model. The model parameters were obtained by using a modified rule-of-mixture procedure and validated against the experimental results. The model can be applied in numerical simulations of complex chiplet packages to evaluate stresses and reliability risks of the interconnect structure.
Scanning electron microscope digital image correlation (SEM-DIC), also referred to as high-resolution digital image correlation (HR-DIC), is a powerful method to measure displacements and strains at the micro to nanoscale. While SEM-DIC is gaining popularity, the nature of various errors in SEM-DIC is not clear. To advance the practice, this work seeks a more extensive and cohesive understanding of the types and causes of errors in SEM-DIC. Previous works have identified SEM imaging errors that are problematic for DIC, including spatial distortions, drift distortions, noise, stabilization errors, and line jumps. The work presented here outlines a unique, interlaboratory, round-robin format to investigate how beam and hardware settings can optimize SEM-DIC image quality. Characterization using multiple SEMs of different vendors, models, and types (e.g., electrostatic and electromagnetic columns) helps identify the types, magnitudes, and causes of SEM-DIC errors, as well as the optimum conditions to reduce such errors. As part of the iDICs round-robin challenge, over 2,000 total SEM images, which are available as an open-access dataset, were analyzed in this study, comprising images from five SEMs, two sample patterning types, and two magnifications. To quantify SEM-DIC errors, this work developed new error metrics to quantify the severity of line jumps, left-edge smear, horizontal skewing, vertical skewing, and translational drift. This round-robin study found that most SEM-DIC experiments should utilize high beam voltages (e.g., 30 kV), fast dwell times (e.g., 1 µs), low to moderate beam currents (e.g., less than 1 nA), no line averaging/integration, and cropping of the left-most portion of images.
Triply periodic minimal surface (TPMS) lattices offer exceptional multifunctional properties but often underperform mechanically compared to analytical predictions. The origin of this discrepancy remains insufficiently understood. This study aims to identify whether the observed underperformance of TPMS structures stems primarily from geometric inaccuracies during fabrication or from intrinsic structural instability. Schwarz Primitive TPMS lattices were additively manufactured using Carbon3D’s Digital Light Synthesis (DLS) process and characterized using X-ray computed tomography (XCT) for geometric fidelity. Compression experiments and nonlinear finite element simulations were then performed to correlate geometric deviations with mechanical performance. Parametric simulations were used to assess sensitivity to off-axis loading, and an external bracing concept was introduced computationally to enhance stability. XCT analysis confirmed that the printed lattices exhibited near-perfect geometric fidelity, with a voxel-wise Dice similarity coefficient of approximately 0.98 between the CAD model and the reconstructed geometry, yet compression tests revealed pronounced global buckling and high sensitivity to angular misalignment. Simulations demonstrated that as little as 1° of off-axis loading caused a > 15
There exists no experimentally validated indentation method to uniquely determine the plastic properties of a material whose hardening behavior is defined with a three-parameter model. The present work aims to systematically investigate non-unique solutions associated with existing and newly proposed indentation methods, and to study the possibility and implications of pressure-induced strengthening during indentation. The residual profiles left by spherical indentation in four materials with different strain hardening behavior were measured with a profilometer. Inverse finite element analysis of the indentation, iterating over hardening parameters to fit the experimental residual indentation profile, was used to map non-unique solutions. The ability of additional spherical indents of varying depth and of post-mortem microhardness measurements to identify unique solutions was assessed. Non-unique solutions of high work-hardening materials had large differences in flow behavior, enabling their distinguishability by microhardness measurement after spherical indentation, but not by multiple indents to varying depth. Improved agreement with uniaxial tension data was achieved through inclusion of a pressure-dependent plasticity model over assumed pressure-independence. A method was established to uniquely determine a three-parameter hardening model using indentation techniques combining spherical indentation, contact profilometry, and Vickers microhardness before and after spherical indentation. Constitutive properties obtained from indentation tests are suggested to overestimate material strength if pressure-induced strengthening is not accounted for.
Liquid crystal elastomers (LCEs) exhibit unique mechanical properties derived from its coupled rod-like liquid crystals (LCs) and polymer chains. They are promising materials in many applications such as artificial muscle, soft robotics, and energy dissipation devices. However, a clear understanding of the stress-director coupling mechanism across different patterned LCEs remain limited. This work patterns LCEs with both monodomain and polydomain regions to create monodomain-polydomain (MP) LCEs and illustrate the stress-director coupling associated with various patterns. Using two-stage thiol-acrylate Michael addition photopolymerization (TAMAP) reaction, we fabricate MP LCEs through sequentially curing selected regions with or without pre-stretching. We then apply uniaxial loading to different MP LCEs and characterize the strain distribution and director reorientation both experimentally and computationally. By changing the director angle in monodomain regions and the geometry of polydomain regions, we modulate the shear compliance and relative stiffness between monodomain and polydomain regions. As a result, we demonstrate the distinct deformation in various MP LCE patterns and reveal the driving mechanism derived from the interplay between stress-director coupling and geometric constraints. In conclusion, this study presents thorough understanding about the stress-director coupling effect on the deformation of MP LCEs and provides design guidelines for patterned LCEs.
The interlayer temperature (ITe) applied during Wire Arc Additive Manufacturing (WAAM) has an impact on the productivity of the process and the mechanical properties of the metal obtained. Self-heating measurement techniques have proven to be an effective means of rapidly assessing the fatigue response of materials. The paper investigates self-heating during fatigue of WAAM-fabricated 2209 duplex stainless steel as a function of the ITe considered during the fabrication. Temperature measurements were performed by infrared thermography and thermocouples during accelerated fatigue tests. The latter consisted of cyclic loading with a continuously increasing stress amplitude. The thermal data were post-processed by Heat Source Reconstruction (HSR), relying on the heat diffusion equation, to quantify the mechanical dissipation per cycle (in kJ.m–3/cycle) as a function of the stress amplitude. Continuous mechanical dissipation vs. stress amplitude relationships were obtained for three ITe values: 150 °C (maximum temperature recommended by the wire supplier) as well as 350 °C and 550 °C, leading to productivity gains during printing of approximately 3 times and 7 times respectively. 1) For a given ITe, the horizontal specimens exhibit better expected fatigue performance compared to the vertical specimens; 2) As the ITe increases, expected fatigue performance deteriorates; 3) However, the stress amplitude corresponding to the onset of mechanical dissipation is nearly the same regardless of the ITe, suggesting that the fatigue benefit of a low ITe for low stress amplitudes is minor compared to the loss of productivity during material printing.
Soft hydrated polymer networks are widely used as model systems for studying the response of biological tissues subjected to high strain-rate loading. While inertial cavitation generates extreme localized deformation fields, the effect of repeated cavitation events on the surrounding material remains poorly understood. This work investigates how repetitive cavitation modifies the microstructure and mechanical response of hydrogels with distinct network architectures. Laser-induced cavitation experiments combined with high-speed imaging, confocal microscopy, and inertial microcavitation rheometry are performed on chemically crosslinked polyacrylamide, physically crosslinked gelatin, and fibrous collagen networks subjected to repeated cavitation events. The results show that the dominant material modification occurs during the first cavitation event, which generates a localized near-field region surrounding the bubble that governs subsequent bubble dynamics. Chemically crosslinked polyacrylamide exhibits localized anisotropic damage features consistent with irreversible bond rupture, whereas physically crosslinked gelatin displays more diffuse structural rearrangement associated with reversible network junctions. Collagen networks exhibit strongly heterogeneous responses governed by the interaction between the cavitation deformation field and the intrinsic fiber architecture. These findings demonstrate that repetitive cavitation primarily probes a pre-modified material region created by the initial event and that the nature of this modification depends strongly on network topology.
There is an increasing demand for cast glass for load-bearing applications in the built environment. This material often contains bulk flaws; more so when for example waste cullet is used. A substantial obstacle to a wider application of such glass components is the lack of reliable methods for evaluating the effect of these bulk flaws on the mechanical performance of the material. Current standardized strength testing methods for glass focus on surface and edge characterization of thin, homogeneous elements. This paper identifies existing destructive methods with potential for measuring the tensile strength of glass and other brittle materials; and assesses to what level they give information about the bulk strength in the presence of bulk flaws. A literature review is conducted on existing destructive testing methods in use for brittle solids from various research domains and end applications. Existing methods are summarized, and their applicability for volumetric glass is critically assessed and discussed. The selected methods are classified, based on stress state, stress distribution and stressed volume, accuracy, consistency and verifiability, complexity and precision required for the test specimens, and the availability of the required test equipment. Subsequently, the various advantages and limitations of the tests are summarized. Several recommendations are made. The direct uniaxial tensile test is recommended for testing bulk flaws under a uniaxial tensile stress state, while the ultrasonic tensile test is discussed as a promising alternative. For biaxial testing the sphere compression test is proposed. Further physical experiments are recommended to assess their reliability and practicality.
The relationship between molecular-scale chain scission and bulk viscoelasticity in soft polymer networks remains incompletely understood, particularly in multiple network elastomers, where energy dissipation arises from the interaction between irreversible chain-scission damage and reversible time-dependent mechanics. This study aims to elucidate how cumulative, progressive chain-scission damage influences bulk viscoelasticity in double network elastomers through both experiments and constitutive modeling. A non-swelling, platinum-cured silicone double network elastomer was synthesized and served as a model system to investigate damage-induced effects on viscoelasticity. Cyclic tensile loading was applied to introduce systematically controlled chain-scission damage. The changes in viscoelastic properties were characterized via stress relaxation tests and dynamic mechanical analysis. A constitutive model coupling hyperelasticity with damage-induced viscosity through stretch-mediated chain-scission kinetics and chain-length-dependent disentanglement kinetics was established to describe the observed damage-viscosity coupling. Experiments revealed that cumulative bond breaking in the double network elastomer contributes not only to Mullins-type softening but also to measurable increases in apparent relaxation time and viscoelastic dissipation rate. The proposed model successfully reproduced damage-related effects, including both irreversible primary hysteresis caused by network damage and narrower, persistent secondary hysteresis due to damage-induced viscoelastic dissipation. Although the damage-induced viscoelastic dissipation was small compared to the energy directly dissipated by bond breaking, our results provide direct experimental evidence and quantification that internal molecular damage can modulate bulk time-dependent constitutive behavior. These findings lay the foundation for predictive modeling of dissipative mechanics mediated by damage–viscoelasticity coupling in complex multiple network elastomers.
Chemomechanically driven degradation at solid electrolyte-lithium metal interfaces is a critical barrier to the reliability of solid-state lithium-ion batteries. Although interphase formation at these interfaces is well recognized, how reaction-induced deformation and stress evolution depend on electrolyte microstructure remains poorly understood. This study aims to directly quantify the coupled evolution of interphase growth, deformation, and stress, and to determine how electrolyte microstructure influences stress localization and fracture during interphase formation. An integrated in situ experimental platform combining optical imaging, mechanical load measurement, and electrochemical impedance spectroscopy was developed to characterize interphase growth and stress evolution in a model sulfide electrolyte (Li₁₀SnP₂S₁₂). Reaction-induced volumetric strain and interphase roughness were quantified from operando imaging, and finite element simulations incorporating reaction-induced eigenstrain were performed to resolve stress localization mechanisms. Interphase growth kinetics were comparable across microstructures; however, dense electrolyte pellets exhibited larger reaction-induced volumetric strains, pronounced interphase roughness, sustained pressure buildup, and tensile microcracking despite globally compressive loading. Simulations revealed that rough interphase morphologies generate substantial localized tensile stress through geometric stress amplification, explaining the observed cracking behavior. These results demonstrate that electrolyte microstructure critically governs how interphase evolution translates into stress localization and fracture, highlighting microstructural control as a key strategy for mitigating chemomechanical degradation in solid-state lithium-ion batteries.
The existing analytical models used to identify the transverse elastic modulus from single fiber transverse compression (SFTC) test almost all consider a circular cross-section. Only one work has proposed an adaptation for elliptical cross-section which still fails to accurately reproduce the force-displacement curve for high ellipticity. The aim of this study is to introduce a novel analytical model capable of faithfully replicating the transverse behavior of elliptical fibers during SFTC test. To take into account the ellipticity of the fiber, the analytical model of Jawad and Ward is adapted using an equivalent contact radius derived from Hertzian contact theory. The proposed model is validated through a finite element analysis (FEA). From the force/displacement curve obtained with the finite element analysis, the transverse elastic modulus of elliptical fibers (with ellipticity varying from 0 to 0.8) is correctly identified, by inverse method, with the proposed model. The maximum relative difference between the identified modulus and that defined in the FEA remains less than 1.2
Strain gauges used for strain measurement in mechanical testing are pasted manually, resulting in discrepancies between the actual measurement direction and the theoretical measurement direction. These deviations lead to measurement errors, which are more pronounced in high strain gradient regions such as openings, reinforcements, and notches. The actual direction of the strain gauge measurement cannot be determined directly. This study aims to accurately determine the actual measurement direction of strain gauges using a non-contact method. A non-contact method for precise strain gauge orientation is proposed. By combining solder joints and boundary features, high-precision strain gauge recognition and pixel acquisition for orientation determination are achieved. A binocular vision method is employed to locate the coordinates of the image pixels, thereby determining the measurement direction of the strain gauges. The proposed method has been validated through an experiment on a cylindrical structure commonly used in aerospace engineering. The results showed that the angular errors between the values obtained by this method and the standard values ranged from 3.39° to 5.6°. The proposed precise orientation method for strain gauges, based on solder joints and boundaries, can determine the high-precision measurement directions of strain gauges.
