Surface Strain Research Articles

Experimental and theoretical study on mechanical performance of Fe-SMA/steel single lap joints

The activated iron-based shape memory alloy (Fe-SMA) can introduce considerable prestress in the damaged zone of deteriorated steel structures through bonding technologies. In China, it has been successfully applied to several kilometer-span steel bridges, such as Sutong Bridge and Hangzhou Bay Bridge. The shear and interfacial performance of steel-to-Fe-SMA plates are crucial issues in bonding Fe-SMA to reinforce deteriorated steel structures, which remain unclear. This paper investigates the shear characteristics of Fe-SMA/steel single lap joints (SLJs), considering the effects of adhesive types, adhesive layer thicknesses and overlap lengths. The stress distribution and the interfacial shear stress at the overlap zone are obtained through experiments, and the damage evolution and load-transfer mechanisms of adhesive layers are analyzed. The experimental outcomes indicate that the maximum tensile stresses of Fe-SMA plates can reach 61 % of their ultimate strength. The failure modes and ultimate load of Fe-SMA/steel SLJs are affected by adhesive types. Interface failure occurs in CH 120 and PCMdur™-15 specimens, whereas interface, cohesive and mixing failure are formed in Sika 31 specimens. Due to the adverse effects of adhesive layer defects, out-of-plane bending moment, and damage accumulation of the adhesive layers, the distribution of surface strain and interfacial shear stress of all specimens are mainly at the effective overlap zone. For an efficient engineering design, the linear and polynomial fitting models of cohesive zone models with different adhesive types and adhesive layer thicknesses are proposed based on experiments. The experimental and theoretical achievements can provide design recommendations for deteriorated steel structures rehabilitated by bonding Fe-SMA.

A piecewise inverse finite element method for shape sensing of the morphing wing fishbone

The shape sensing technology plays a significant role in enhancing the structural performance and flight efficiency of the morphing aircraft by providing feedback to actuation and control systems in real time. The inverse finite element method (iFEM) is a fast, accurate, and robust shape-sensing method based on in-situ surface strain measurements. However, the conventional iFEM becomes less effective when applied to real engineering structures. Thus, this paper proposes a piecewise iFEM (P-iFEM) based on a two-node inverse Hermite beam element (iHB2) for the load-bearing structure of the morphing wing. The P-iFEM method discretizes the structure into a combination of rigid and elastic parts, based on the geometry of the structure when assembling the inverse elements. The Hermite polynomial shape function in iHB2 is adopted to increase the reconstruction efficiency, as only one degree of freedom of deflection is required to achieve the C1-continuity to reconstruct the displacement fields. The high accuracy and efficiency of the proposed method are validated with a numerical fishbone model. Finally, the proposed method is applied to a fishbone structure of a real adaptive deformed wing with high accuracy.

CO2 Hydrogenation to CH3OH on Metal-Doped TiO2(110): Mechanisms, Strain Effect and a New Thermodynamic-Kinetic Relation.

Surface strain and linear thermodynamic-kinetic relation are interesting topics in catalysis. Development of low temperature methanol catalysts of high activity and selectivity is of particularly importance for conversion of CO2 to methanol. In the present paper CO2 hydrogenation to methanol on Znx@TiO2(110) (x=0-2) was explored using density functional calculations and microkinetic simulations. The reaction mechanisms on the three model systems were determined and it is shown that Zn2@TiO2(110) is the most active. The most favorable pathway on Zn2@TiO2(110) is identified and CO2+H to HCOO is found to be the rate-controlling step. It is demonstrated that there is a linear relation (named AEB relation) between the adsorption energies of the initial states and the barriers for the controlling step on the 18 systems studied. Calculations on strained surfaces show that the AEB relation exists within ±1 % strain. Sr2@TiO2(110) and -1 % strained CaZn and ZnCu doped TiO2(110) are potential good low temperature catalysts and deserve experimental testing.

Experimental and numerical study of impact resistance and compression properties after impact of none-felt needled composites

In this paper, the impact and after-impact compression (CAI) properties of new none-felt needled composites were investigated by finite element and experimental methods. Micro-CT and digital image correlation (DIC) were used for structural characterization and recording surface strains in CAI specimens. The impact and CAI finite element models of needled composites were developed, and the damage mechanisms were analyzed. The results showed that the impact and CAI properties of none-felt needled composite were substantially improved. In the impact experiments, the failure firstly occurred in the interlayer and gradually extended to the fiber layer. In the CAI experiment, the damage gradually extended from the impact damage region to the specimen edges, and the specimen finally failed when the damage with the specimen edges extended together. The established finite element model agreed well with both the impact and CAI tests, and the errors were less than 5 % and 10 %.

Effective multiscale structural analysis of thick sandwich structures with 3D woven composite face sheets and a soft core based on coupled micromechanics and refined zigzag theory

In this study, a novel multiscale analysis technique is presented for predicting the mechanical behavior of 3D woven composites. To this end, the model of the representative unit cell (RUC) is generated using SOLIDWORKS computer-aided design package by taking the optical microscopic images as a reference. The fiber volume fractions (FVF) of the impregnated yarns are calculated using the roving parameters and the dry fiber density for each tow separately. Homogenized properties are obtained by utilizing the finite element analysis (FEM) software ABAQUS. The proposed method simplifies the meso-modeling process of 3D woven composites as it does not require CT scanning for geometry generation or sophisticated localized fiber volume fraction measurements. The verification of the current model is carried out both in the meso scale where the RUC surface strains are compared with DIC results and in the macro scale where tensile and flexural tests are simulated and compared with the experiments. Finally, the applicability of this method is demonstrated through an assessment study of the 3D woven composites as facesheets in thick sandwich structures in an isogeometric refined zigzag framework.

A unified design method for 2D auxetic metamaterials based on a minimal auxetic structure

Auxetic metamaterials are architected structures that possess a unique property known as a negative Poisson’s ratio. This remarkable characteristic enables them to expand or contract in a direction perpendicular to stretch or compression. Due to their exceptional attributes such as energy absorption and fracture resistance, these auxetic metamaterials hold great promise for various applications across multiple domains.However, the widespread development of these materials has been hindered by the absence of an efficient design method. Addressing this limitation, our work introduces a minimal 2D auxetic structure and a corresponding design approach that comprises two geometric transformations. This design method not only allows for the replication of existing auxetic structures but also facilitates the creation of novel structures. Additionally, it enables the classification of these structures into six distinct categories.To enhance the understanding and standardization of these structures, we propose a naming protocol and define their associated unit cell. Furthermore, we explore the possibilities of tessellations within this framework. Finally, we examine the auxetic structures from the perspective of surface strain, which is closely linked to the Poisson’s ratio, the Bulk modulus and compressibility.

High cycle fatigue behavior of additively manufactured Ti-6Al-4V alloy with HIP treatment at elevated temperatures

The fatigue tests at 200 °C and 400 °C were conducted to investigate the elevated-temperature fatigue behavior of additively manufactured (AM) Ti-6Al-4V alloy with hot isostatic pressing (HIP) treatment. Since the manufacturing defects (i.e., pores) were significantly reduced by HIP treatment, no specimen failed from the pores. Consequently, the present AM Ti-6Al-4V alloy behaved superior to that without HIP treatment. Moreover, the specimens exhibited different failure mechanisms at 200 °C and 400 °C. Fatigue crack initiation at 200 °C mainly was due to surface deformation and strain localization, while the cause became fracture of surface oxygen-rich layer at 400 °C.

Influence of microvascular structured void content on composites subjected to in-plane shear loads

Microvascular fiber reinforced composites can be used as multifunctional structures capable of self-healing, thermal regulation, and communication, among others. The inclusion of a small volume of microchannels generally has a minimal impact on the mechanical properties of the composites. In the current work, the in-plane shear properties of microvascular composites containing embedded stainless steel and wall-less microchannels produced through sacrificial material removal were characterized for the first time. Microvascular unidirectional composites were manufactured with precisely located microchannels both aligned with and transverse to the fiber direction, and their in-plane shear properties were tested. Microchannels aligned with the fiber direction were shown to cause a substantial (−7%) decrease in shear strength but had no effect on shear modulus or failure strain. Distortion of the laminate surface around the channels oriented transverse to the fiber axis was observed, resulting in an increase in void content (1–4%), a 9% loss in shear modulus, and a 27% loss in shear strength. The use of a caul plate made the loss in shear strength statistically insignificant, increased the shear modulus by 12–15%, and decreased the shear strain by −25% relative to the baseline composite without microchannels. Digital image correlation showed that the surface strains for transversely oriented samples were interrupted near the microchannels, but post-test x-ray computed tomography and optical microscopy do not show crack redirection. The newfound understanding of the shear response of microvascular composites provides important insights that will enable future engineering designs of multifunctional aerospace structures.

Compressed Ru skin on atomic-ordered hexagonal Ru-Ni enabling rapid Volmer-Tafel kinetics for efficient alkaline hydrogen evolution

Ru-based materials are promising electrocatalysts for hydrogen evolution reaction (HER) owing to their low-cost (one twenty-fifth of Pt) and similar Gibbs free energy of H* adsorption (ΔGH*) to that of Pt. However, the inadequate ability for the water dissociation of Ru catalysts is significantly impeding the water splitting efficiency. In this work, we demonstrate an atomically ordered hexagonal Ru-Ni alloy with compressive-strained Ru skin as a high-performance HER catalyst for significantly boosting the water dissociation. The Ordered Ru-Ni achieves an optimized catalytic activity for alkaline HER with a low overpotential of 23 mV at 10 mA cm−2, Tafel slope of 25.9 mV dec−1 and superior mass activity of 4.83 A mg−1Ru, which is 15.1 times higher than Ru/C. According to DFT calculations, the ordered RuNi core imposes homogeneous compressive strain on the Ru skin, resulting in an optimum binding energy towards H*/OH* intermediates on Ru active sites for rapid Tafel step kinetics. Moreover, the decreased H2O dissociation energy barrier of Ordered Ru-Ni suggests a promoted Volmer-Tafel kinetics is achieved, significantly boosting the overall HER efficiency. This work provides a practical avenue for surface strain engineering of Ru-based catalysts to promote the HER activity.

Bending creep behaviour of various polymer films analysed by surface strain measurement.

Understanding the temporal bending deformation of polymer films is key to designing mechanically durable flexible electronic devices. However, such creep behaviour under persistent bending remains unclear due to a lack of precise and accurate bending strain analysis methods. Herein, we quantitatively analysed the bending creep behaviour of various polymeric films using our developed strain measurement method that can precisely measure surface strain from optical diffraction. The surface strain measurement reveals that bending creep deformation differs depending on the polymer structure. The four-element Burgers model was employed to model the temporal strain increase on the bending surface successfully. By fitting the four-element model to the time course of the measured surface strain, we found that each polymer film has a different threshold surface strain for the appearance of bending creep deformation. Such disparity in the bending creep behaviour can be explained by the difference in strain energy density between the polymer films and their elastic model; polymer films with a small strain energy density difference show small bending creep deformation. The results obtained in this study contribute to the elucidation of the bending creep behaviour of polymer films and the development of flexible electronic devices operated under persistent bending.

Damage assessment of concrete beams repaired with basalt fiber-reinforced polymer sheets through digital image correlation and acoustic emission

Basalt fiber-reinforced polymer (BFRP) has high mechanical strengths as a repairing material but exhibits low ductility. This paper investigates the damage process of reinforced concrete beams repaired using BFRP sheets, aimed at understanding the underlying mechanisms of achieving structural ductility when BFRP sheets are used. The damage process was assessed using digital image correlation (DIC) and acoustic emission (AE) techniques applied to monitor surface and internal damages of three full-scale concrete beams subjected to four-point bending. A beam was first loaded to crack, then repaired with BFRP sheets, and finally reloaded to failure. Surface strain fields and cracks were monitored using a DIC method, and cracking events were monitored using AE sensors deployed at different positions of the beams. The AE signals were analyzed to assess the damage process. The test results indicated that (1) tensile cracks predominated throughout the loading process; (2) the BFRP sheets hindered the widening of cracks and promoted the generation of fine cracks; and (3) the development of concrete cracks promoted interfacial debonding at steel-concrete and BFRP-concrete interfaces. A combination of different types of cracks and interfacial debonding helped the repaired beam achieve ductile flexural behaviors.

Three-dimensional surface strain sensor based on PDMS/LIG composite film with adjustable electromechanical performance

Flexible strain sensors play a crucial role in health monitoring, smart wearable devices, and human–machine interaction. Three-dimensional surface evaluation methods for strain sensors offer advantages by being closer to actual strain, featuring a larger working range, and being more suitable for multidirectional strain. In this study, a three-dimensional (3D) surface strain sensor based on polydimethylsiloxane/laser-induced graphene (PDMS/LIG) composite films has been developed. The electromechanical properties of this sensor, encompassing 3D strain range and sensitivity, can be adjusted by manipulating laser parameters and LIG patterns. The key to attaining these specific characteristics lies in the intentional design of crack types and orientations on the sensor's surface. Remarkably, the line-vertical (LV) sensor exhibits outstanding sensitivity with a GF of 211.3. The line-parallel (LP) sensor achieves a GF of 115.1. Additionally, it demonstrates a stretching range of 25% and maintains stable performance over an extensive number of strain/release test cycles (more than 3000 cycles). With these advantages, the 3D strain sensor can not only be applied in human activity monitoring but also monitoring pressure within microchannels in microfluidic chips, suggesting promising applications in the health and medical fields.

Experimental Research on Impact Resistance Test of Polycrystalline Diamond Compact Based on Digital Image Correlation Method

In this study, the impact resistance of Polycrystalline Diamond Compact (PDC) was studied with DIT drop weight tester and high speed camera. The surface of PDC was analyzed by Digital Image Correlation (DIC). The reason of impact failure of PDC was obtained by using the surface strain field of PDC. The results show that local delamination occurs near the impact point of the polycrystalline layer. The brittle fracture occurs at the maximum tensile strain of the impact resistant composite sheet. The quantitative relationship between the surface strain and the image obtained by DIC can effectively reflect the whole process of PDC composite failure, and can reasonably explain the failure process of PDC composite, and provide scientific research methods for engineering applications.

Experimental and virtual testing of bone-implant systems equipped with the AO Fracture Monitor with regard to interfragmentary movement.

Introduction: The management of fractured bones is a key domain within orthopedic trauma surgery, with the prevention of delayed healing and non-unions forming a core challenge. This study evaluates the efficacy of the AO Fracture Monitor in conjunction with biomechanical simulations to better understand the local mechanics of fracture gaps, which is crucial for comprehending mechanotransduction, a key factor in bone healing. Through a series of experiments and corresponding simulations, the study tests four hypotheses to determine the relationship between physical measurements and the predictive power of biomechanical models. Methods: Employing the AO Fracture Monitor and Digital Image Correlation techniques, the study demonstrates a significant correlation between the surface strain of implants and interfragmentary movements. This provides a foundation for utilizing one-dimensional AO Fracture Monitor measurements to predict three-dimensional fracture behavior, thereby linking mechanical loading with fracture gap dynamics. Moreover, the research establishes that finite element simulations of bone-implant systems can be effectively validated using experimental data, underpinning the accuracy of simulations in replicating physical behaviors. Results and Discussion: The findings endorse the combined use of monitoring technologies and simulations to infer the local mechanical conditions at the fracture site, offering a potential leap in personalized therapy for bone healing. Clinically, this approach can enhance treatment outcomes by refining the assessment precision in trauma trials, fostering the early detection of healing disturbances, and guiding improvements in future implant design. Ultimately, this study paves the way for more sophisticated patient monitoring and tailored interventions, promising to elevate the standard of care in orthopedic trauma surgery.

Dynamic model for the strain-modulated spectral reflectance of the human skin in vivo.

Hyperspectral imaging (HSI) offers a wealth of information regarding human skin. In this study, we established a dynamic skin spectral reflectance model (DSSR) relating the reflectance to skin surface strain, considering multi physiological and physical parameters of the skin. Experimentally, by HSI, we measured the reflectance variance of the forearm skin in vivo caused by the surface strain, and assessed these key parameters. For the human skin in vivo, within the strain range covered in this paper, stretching increases spectral reflectance, while compression decreases it. Our proposed model provides a possibility for non-contact strain measurement and health monitoring on the skin in vivo based on HSI.

Interference effect and Raman depolarization behavior in MoO2 bubbles

Here, MoO2 bubbles are firstly found in MoO2 nanosheets (NSs) synthesized by chemical vapor deposition and exposed to air for 2–3 years. Interestingly, the Newton’s rings are clearly observed in Raman map of MoO2 bubbles. Meanwhile, it’s found that the height of bright rings close to the 1/2, 2/2, 3/2 of the laser wavelength, confirming that the Newton’s rings in Raman map are caused by the laser interference on the surface of bubbles. At the same time, based on simple membrane theory, the adhesion energy 0.15 and 1.08 J/m2 between MoO2 NSs and different SiO2/Si substrates are extracted. Moreover, Raman depolarization effect is observed on the surface of MoO2 bubbles. As the aspect ratio of bubbles increases from 0.16 to 0.21, the relative-depolarization ratios of 205 cm−1 and 750 cm−1 phonon modes are gradually increased from 18% to 46% and 10–36%, respectively. The Raman depolarization behavior should be ascribed to the surface strain of MoO2 bubbles leading to the asymmetric changes of photoelastic tensor in all directions of the crystal. This finding maybe provides a reference for regulating the polarization characteristics of MoO2 by adjusting its surface strain and ultimately achieving application in the field of photonics.

Inverting Geodetic Strain Rates for Slip Deficit Rate in Complex Deforming Zones: An Application to the New Zealand Plate Boundary

AbstractThe potential for future earthquakes on faults is often inferred from inversions of geodetically derived surface velocities for locking on faults using kinematic models such as block models. This can be challenging in complex deforming zones with many closely spaced faults or where deformation is not readily described with block motions. Furthermore, surface strain rates are more directly related to coupling on faults than surface velocities. We present a methodology for estimating slip deficit rate directly from strain rate and apply it to New Zealand for the purpose of incorporating geodetic data in the 2022 revision of the New Zealand National Seismic Hazard Model. The strain rate inversions imply slightly higher slip deficit rates than the preferred geologic slip rates on sections of the major strike‐slip systems including the Alpine Fault, the Marlborough Fault System and the northern part of the North Island Fault System. Slip deficit rates are significantly lower than even the lowest geologic estimates on some strike‐slip faults in the southern North Island Fault System near Wellington. Over the entire plate boundary, geodetic slip deficit rates are systematically higher than geologic slip rates for faults slipping less than one mm/yr but lower on average for faults with slip rates between about 5 and 25 mm/yr. We show that 70%–80% of the total strain rate field can be attributed to elastic strain due to fault coupling. The remaining 20%–30% shows systematic spatial patterns of strain rate style that is often consistent with local geologic style of faulting.

Anomaly detection from slope surface strain using linear regression

Anomaly detection from slope surface strain using linear regression

A Field Study to Measure the Surrounding Stress of Rock and Supporting Structure of a Steep Tunnel with a Combination of Hard and Soft Rock Layers under Plate Compression

Tunnels excavated in a combination of hard and soft rock strata with high ground stress are prone to large deformations, collapse, and other disasters. The Yongfeng Tunnel, a reconstruction and expansion of the G544 line, suffered severe high ground stress from plate compression. This paper studied the surrounding rock pressure and supporting structure stress characteristics of tunnels with a combination of hard and soft rock strata with high ground stress by using earth pressure cells, surface strain gauges, and embedded strain gauges to test all stress related to the surrounding rock, primary support, and secondary lining. It was found that the contact pressure (P1) between the initial support and the surrounding rock and the contact pressure (P2) between the initial support of the leading tunnel were distributed in the direction of vertical stratification, while the contact pressures (P1 and P2) of the lagging tunnel were different due to the excavation unloading of the leading tunnel. The maximum stress positions of the initial support of the leading tunnel and the lagging tunnel were located in the left arch waist and the vault, respectively. However, the maximum stress position of the secondary lining was generally located on the side wall. The research results presented herein can guide future tunnel construction projects.

Heterogeneous Catalyst Coating for Boosting the Activity and Chromium Tolerance of Cathodes for Solid Oxide Fuel Cells

AbstractA challenge hindering the development of durable solid oxide fuel cells (SOFCs) is the significant performance degradation of cathodes owing to poisoning by volatile Cr originating from the Fe─Cr alloy interconnect. Herein, a heterogeneous catalyst coating, composed of Ba1−xCe0.8Gd0.2O3–δ and BaCO3, remarkably improves the oxygen adsorption, dissociation capability, and Cr resistance of a La0.6Sr0.4Co0.2Fe0.8O3–δ (LSCF) cathode is demonstrated. The coherent heterointerface interactions formed between the catalyst coating and LSCF result in varied levels of surface strain and electrostatic interactions, significantly suppressing Sr surface segregation on LSCF. A single cell with the catalyst coating‐decorated LSCF (CC‐LSCF) achieves a peak power density of 1.73 W cm−2 at 750 °C, with no noticeable performance degradation for 100 h. The CC‐LSCF cathode also exhibits outstanding durability under accelerated Cr poisoning conditions, compared with the tremendous degradation rate of 0.42% h−1 for the bare LSCF cathode. The enhanced Cr resistance is attributed to synergy induced by the stabilization of the lattice Sr cations by heterointerface interactions and the remarkable structural stability of the catalyst coating under Cr poisoning conditions. The novel heterointerface engineering strategy in this study provides insight into the design and development of active and Cr‐tolerant cathodes.