Strain Measurements Research Articles

Flexible Strain Sensors with Ultra-High Sensitivity and Wide Range Enabled by Crack-Modulated Electrical Pathways

Abstract This study presents a breakthrough in flexible strain sensor technology with the development of an ultra-high sensitivity and wide-range sensor, addressing the critical challenge of reconciling sensitivity with measurement range. Inspired by the structure of bamboo slips, we introduce a novel approach that utilises liquid metal to modulate the electrical pathways within a cracked platinum fabric electrode. The resulting sensor demonstrates a gauge factor greater than 108 and a strain measurement capability exceeding 100%. The integration of patterned liquid metal enables customisable tuning of the sensor’s response, while the porous fabric structure ensures superior comfort and air permeability for the wearer. Our design not only optimises the sensor’s performance but also enhances the electrical stability that is essential for practical applications. Through systematic investigation, we reveal the intrinsic mechanisms governing the sensor’s response, offering valuable insights for the design of wearable strain sensors. The sensor’s exceptional performance across a spectrum of applications, from micro-strain to large-strain detection, highlights its potential for a wide range of real-world uses, demonstrating a significant advancement in the field of flexible electronics.

Bending moment calibration for rotational bending fatigue testing machine based on strain measurement

Abstract Rotational bending fatigue testing is an important method to evaluate the fatigue of metal materials under cyclic loading. Specifically, the fatigue strength is evaluated through repeated rotational bending under complex loads with the accuracy affected by the bending moment. Here, a method based on strain measurements is proposed for calibrating the bending moment of rotational bending fatigue testing machines. Specifically, the strain of a metal sample under loading with resistance strain gauges was recorded using a strain acquisition system to measure the bending moment. The positions of strain gauges were designed according to the principle of strain measurements to establish a calibration program. Three metal samples of different sizes were tested on two types of rotational bending fatigue testing machines, and the measurement uncertainty was evaluated and verified. The experimental results showed that the proposed method measured and calibrated the bending moment of rotational bending fatigue testing machines rapidly, conveniently, and accurately. The results also provide a practical reference for research and application in related fields.

Strain As An Indicator For Stress Fractures In Racehorses

Abstract The horse racing industry, despite its financial significance, grapples with significant welfare issues, particularly stress fractures in racehorses. Third metacarpal (MC3) bone fractures, constituting about one-third of all limb fractures, severely impact horse health and performance. The frequent occurrence of condylar fractures in the MC3, often resulting in bone comminution, poses high risks-sometimes necessitating euthanasia, and complicates the management and recovery processes for the rest. Comprehensive methods for quantitatively determining fracture risks in horses are lacking, with strain measurements on the MC3 during racing conditions showing promise as an indicator of high loads and potential fracture risks. This study investigated the mechanical properties of MC3 under high compressive loads. Six MC3 bones from euthanized horses were instrumented with strain gauge rosettes at four key locations: Lateral Condyle (CondL), Medial Condyle (CondM), Dorsal DistoLateral (DisL) and Dorsal DistoMedial (DisM). Each bone underwent a pre-loading phase and five cycles of 12kN sinusoidal loading to replicate galloping forces. Strain patterns were observed before and after introducing an artificial slot in the lateral condylar groove to simulate a fatigue crack. A strong correlation was found between load and minimum principal strain in both intact and fatigue crack-induced (FCI) bones, with R-squared values over 0.99. Post-FCI, 83% of bones exhibited an increase in the minimum principal strain-load response slope, indicating uniform changes in material behavior. Additionally, a rise in post-FCI y-intercept values across MC3 locations indicated higher initial strain and possible changes in bone properties.

A deep learning based method for left ventricular strain measurements: repeatability and accuracy compared to experienced echocardiographers.

Speckle tracking echocardiography (STE) provides quantification of left ventricular (LV) deformation and is useful in the assessment of LV function. STE is increasingly being used clinically, and every effort to simplify and standardize STE is important. Manual outlining of regions of interest (ROIs) is labor intensive and may influence assessment of strain values. We hypothesized that a deep learning (DL) model, trained on clinical echocardiographic exams, can be combined with a readily available echocardiographic analysis software, to automate strain calculation with comparable fidelity to trained cardiologists. Data consisted of still frame echocardiographic images with cardiologist-defined ROIs from 672 clinical echocardiographic exams from a university hospital outpatient clinic. Exams included patients with ischemic heart disease, heart failure, valvular disease, and conduction abnormalities, and some healthy subjects. An EfficientNetB1-based architecture was employed, and different techniques and properties including data set size, data quality, augmentations, and transfer learning were evaluated. DL predicted ROIs were reintroduced into commercially available echocardiographic analysis software to automatically calculate strain values. DL-automated strain calculations had an average absolute difference of 0.75 (95% CI 0.58-0.92) for global longitudinal strain (GLS), and 1.16 (95% CI 1.03-1.29) for single-projection longitudinal strain (LS), compared to operators. A Bland-Altman plot revealed no obvious bias, though there were fewer outliers in the lower average LS ranges. Techniques and data properties yielded no significant increase/decrease in performance. The study demonstrates that DL-assisted, automated strain measurements are feasible, and provide results within interobserver variation. Employing DL in echocardiographic analyses could further facilitate adoption of STE parameters in clinical practice and research, and improve reproducibility.

Abstract 4131409: Systemic Review and Meta-analysis of Global Longitudinal Strain Changes after Angiotensin Receptor Nephrilysin Inhibitor Initiation in Patients with Heart Failure

Angiotensin Receptor Nephrilysin Inhibitors (ARNi) have been established as a beneficial medication in patients with heart failure (HF). This class of medications has been shown to decrease HF hospitalizations and has been included as one of the pillars in guideline directed medical therapy. Recently, left ventricular (LV) global longitudinal strain (GLS) measurements on echocardiograms have become more common and provide a more precise measurement of LV function than ejection fraction. GLS is now being used as a more intricate way of monitoring improvement in the function of the myocardium, especially in patients with heart failure. This meta-analysis was conducted to determine if treatment with ARNi in HF patients significantly improves myocardial functioning measured by LV GLS. A meta-analysis of 9 studies including observational studies and randomized controlled trials found in a Pubmed search was performed and included patients with heart failure who were initiated on an ARNi for guideline directed medical therapy and had LV GLS measurements taken on an echocardiogram before and after ARNi initiation. The study included patients with heart failure with reduced ejection fraction. Studies were excluded if the patient population did not have a diagnosis of HF and if LV GLS measurements were not available before and after treatment with ARNi. This analysis was performed to determine if initiation of ARNi in patients with HF led to a significant improvement in LV GLS on echocardiography and therefore a significant improvement in myocardial function. There were 9 studies included in the analysis and 879 patients with HF who were treated with ARNi or a control. The change in LV GLS at the conclusion of the study period was measured in both treatment and control groups and the mean difference between the two groups was -1.61 with a 95% confidence interval of (-2.23, -0.98) (p <0.00001). This indicates that the ARNi treatment groups had a significant improvement in GLS compared to the control groups. ARNi initiation was found to significantly improve LV GLS and therefore myocardial function in patients with HF with reduced ejection fraction. LV GLS is a precise measurement of myocardial function. Using this form of measurement in echocardiograms can aid in determining the effect different treatments have directly on myocardial function.

Myocardial Strain Assessment for Early Duchenne Muscular Dystrophy Diagnosis in Pediatric Patients Using Cardiac MRI

Assessing myocardial strain remains challenging, particularly in the pediatric population, due to the smaller heart sizes, higher heart rates, and variability in strain parameters compared to adult populations. This study aimed to investigate the utility of myocardial strain measurements using cardiac magnetic resonance-feature tracking (CMR-FT) for early diagnosis of Duchenne muscular dystrophy (DMD) in pediatric patients. Twenty-eight DMD patients and 20 healthy controls were involved in this study. Global circumferential, longitudinal, and radial strain (GCS, GLS, and GRS) were measured for the left ventricle (LV) using CMR-FT. Segmental strain values only of the inferolateral and anterolateral LV segments in DMD patients without late gadolinium enhancement (LGE) and DMD patients with LGE were compared to the healthy controls. Strain measurements using CMR-FT in DMD patients were considerably lower than those of healthy controls, with all p-values lower than 0.001. DMD patients without LGE showed decreased inferolateral and anterolateral segmental values only relative to healthy controls. The same behavior was maintained for the LV geometry. Multivariable linear regression demonstrated that the end-systole (ES) wall thicknesses and thickening were associated with decreased GCS and GLS. CMR-FT is crucial in detecting cardiac abnormalities in patients with DMD. It represents an innovative imaging biomarker that can detect initial myocardial alterations in DMD cardiomyopathy without relying on gadolinium.

An objective isogeometric mixed finite element formulation for nonlinear elastodynamic beams with incompatible warping strains

AbstractWe present a stable mixed isogeometric finite element formulation for geometrically and materially nonlinear beams in transient elastodynamics, where a Cosserat beam formulation with extensible directors is used. The extensible directors yield a linear configuration space incorporating constant in-plane cross-sectional strains. Higher-order (incompatible) strains are introduced to correct stiffness, whose additional degrees of freedom are eliminated by an element-wise condensation. Further, the present discretization of the initial director field leads to the objectivity of approximated strain measures, regardless of the degree of basis functions. For physical stress resultants and strains, we employ a global patch-wise approximation using B-spline basis functions, whose higher-order continuity enables using much fewer degrees of freedom than an element-wise approximation. For time-stepping, we employ implicit energy–momentum consistent scheme, which exhibits superior numerical stability in comparison to standard trapezoidal and mid-point rules. Several numerical examples are presented to verify the present method.

An investigation of clay percentage variation on composite materials sustainability identification by digital image correlation

ABSTRACT The study focuses on stress and strain evaluation of composite resin material with the reinforcement of clay in the glass-reinforced epoxy composite (GREC). The strain measurement used the DIC technique. The tensile test specimens were prepared from the laminate sheets as per ASTM D638 standard. The influence of nano clay weight percentage such as 2.5%, 3.5%, and 4.5% during preparation of GREC is studied in the article. The fibre orientation angles are 90°, and the fibre volume percentage is 45%. Hand lay-up methods are used to prepare the composite resin material. The samples were tested as per the standardised procedures. The specimen rupture at a localised strain reached a maximum value of 0.01293, 0.01571, and 0.0143 with 2.5%, 3.5% and 4.5% Nano clay, respectively. The material behaviour in terms of major strain (εyy), Poisson’s ratio (µ) and thickness strain (Δt) is evaluated at the gauge length of the specimen. DIC strain measurement clearly demonstrates the 3.5% percentage of clay addition as it yields better results as elastic modulus and tensile strength have improved. The composite resin with clay addition could be used in various applications, such as low-cost housing, structural works, medical devices, automotive panels, etc

Cardiovascular magnetic resonance in β-thalassemia major: beyond T2.

Β-thalassemia major (TM) patients underwent regular transfusions to prevent complications of chronic anemia. However, these regular transfusions result in progressive iron accumulation in vital organs, including the heart. Myocardial iron overload can lead to cardiac dysfunction and ultimately to heart failure. Diagnosis of cardiac dysfunction in β-TM patients is usually made through clinical examination, electrocardiogram, and echocardiography. Cardiac magnetic resonance (CMR), through the measurement of T2* relaxation time, represents the diagnostic modality of choice for assessing myocardial iron overload and guiding the iron chelation therapy. Despite a tailored chelation therapy reducing myocardial iron overload, heart failure remains the leading cause of morbidity and mortality even in well-treated β-TM patients. Advances in CMR, including myocardial strain, parametric mapping (T1, T2, and extracellular volume), and late gadolinium enhancement (LGE) measurements, have expanded its role in the diagnosis, prognosis, and follow-up of these patients. This review seeks to offer a thorough overview of the potential uses of CMR in β-TM, extending beyond the established role of T2* measurement in guiding chelation therapy. It delves into the emerging applications of new CMR imaging biomarkers that could improve the overall management of β-TM patients.

High spatial resolution φ-OFDR based on frequency-shift averaging and rotating vector summation

The coherent fading noise hinders the spatial resolution enhancements of phase optical frequency domain reflectometry (φ-OFDR). To mitigate the coherent fading noise, this study introduces frequency-shift averaging and rotating vector summation for strain measurements. The original Rayleigh backscattering signal was first divided into numerous sub-segments in frequency domain by using the frequency-shift averaging, and each sub-signal segment was transferred into vector signal with both intensity and phase information by using the rotating vector summation. Furthermore, a spatial position correction algorithm is incorporated to counteract the degradation of phase coherent, facilitating large-scale strain measurements. After optimizing the sub-frequency range and overlap ratio of the sub-signal in the frequency domain, we experimentally demonstrated that this method achieves strain measurement with a broad strain range of 2000 με, a high spatial resolution of 0.54 mm, and a high precision of 0.87%.

Global, segmental, and layer-specific two-dimensional speckle tracking echocardiography immediately after acute myocardial infarction as a predictive tool to assess myocardial viability and scar size.

The identification of myocardial scar is key in clinical decision-making after acute myocardial infarction (AMI). However, the gold standard that is cardiac magnetic resonance imaging (CMR) encounters limitations in terms of availability. Two-dimensional speckle tracking echocardiography (2D-STE) may be an accessible alternative in detecting scar and assessing scar transmurality. We aim to evaluate the predictive value of 2D-STE, encompassing measures of global, segmental and layer-specific strain, with respect to myocardial viability and scar size at 6 months follow-up. In 43 patients admitted for primary AMI, we conducted a comparative analysis of strain parameters (including global longitudinal strain (GLS), segmental longitudinal strain (SLS), layer-specific GLS and SLS and the transmural strain gradient from endocardium to epicardium) in relation to conventional echocardiographic parameters at baseline in predicting for scar size and the transmurality index, as measured by CMR, 6 months post enrollment. We demonstrate a moderate correlation between both GLS and conventional echocardiographic parameters, and scar size as well as transmurality index. Wall motion score index exhibited superior predictive performance over GLS and left ventricular ejection fraction in anticipating scar formation. At a cut-off of -13.3% for any scar and -11.5% for transmural scar, SLS can predict scar formation. Layer-specific strain did not provide added predictive value. SLS, but not layer-specific strain, during admission after AMI is an easy and accessible quantitative tool for predicting scar formation and transmurality extent at 6 months follow-up. GLS correlates well with scar size, suggesting its potential utility as a predictive tool.

Myocardial deformation in multisystem inflammatory syndrome in children: layer-specific cardiac MRI insights from a pediatric cohort.

Multilayer strain magnetic resonance imaging (MRI) analysis offers detailed insights into myocardial mechanics and cardiac function by assessing different layers of the heart muscle, enabling a comprehensive understanding of cardiac involvement. This study aims to explore cardiac strain differences between patients with multisystem inflammatory syndrome and a control group at medium-term follow-up, utilizing a layer-specific cardiac magnetic resonance imaging (CMR) approach. In this retrospective study, patients with multisystem inflammatory syndrome in children (MIS-C) and a group of controls who had undergone cardiac magnetic resonance (CMR) imaging were selected and included. CMR was performed 30days after discharge (range 34-341days) for MIS-C patients. TrufiStrain research prototype software (Siemens Healthineers AG, Erlangen, Germany) was used for automated myocardial segmentation and strain calculation, to measure radial strain (RS), circumferential strain (CS), and longitudinal strain (LS) at the epicardial, mid-wall, and endocardial levels. Statistical analysis included Shapiro-Wilk tests, Student t-tests, and Mann-Whitney U tests, ANOVA, and regression analysis, maintaining a significance level of α = 0.05. The study cohort consisted of 32 MIS-C patients (≤ 18years; 14 females) and 64 control participants (≤ 18years; 24 females). Median interval to CMR post diagnosis was 142days (range 34-341) with normal CMR findings for all patients. The mean age of the two groups was similar (MIS-C: 14.2years; controls: 14.1years, P = 0.49). There were no significant differences in height (MIS-C: 164.7cm; controls: 163.9cm, P = 0.84), weight (MIS-C: 68.2kg; controls: 59.4kg, P = 0.11), or body surface area (MIS-C: 1.7 m2; controls: 1.7 m2, P = 0.41). Global strain measurements showed no significant differences between the groups (global LS MIS-C patients - 16.2% vs - 15.7% in controls (P = 0.23); global RS 27.8% in MIS-C patients vs 29.5% in controls (P = 0.35); and global CS - 16.7% in MIS-C patients vs - 16.8% in controls (P = 0.92)). Similarly, layer-specific strain analysis across the endocardial (LS values of - 17.7% vs - 16.8% (P = 0.19), RS of 23.1% vs 24.8% (P = 0.25), and CS of - 19.9% vs - 19.9% (P = 0.92)), epicardial (LS - 14.9% vs - 14.5% (P = 0.31), RS of 31.2% vs 33.1% (P = 0.29), and CS of - 14.1% vs - 14.2% (P = 0.75)), and midmyocardial (LS - 16.5% vs - 16.3% (P = 0.18), RS 29.3% vs 31.8% (P = 0.31), and CS - 17.0% vs - 17.2% (P = 0.95)) levels revealed no significant disparities. The only notable finding was the reduced apical radial strain in MIS-C patients compared to controls (global RS MIS-C 12.4% vs 17.4% in controls, P = 0.03; endocardium RS MIS-C 4.9% vs 10.31% in controls, P = 0.01; epicardial RS MIS-C 17.7% vs 22.6% in controls, P = 0.02; and midmyocardium RS MIS-C 12.5% vs 17.9% in controls, P = 0.02). This study demonstrates that MIS-C does not significantly impact global or layer-specific myocardial strain values, as assessed by CMR, compared to a control group. The lower apical radial strain in MIS-C patients indicates a potential localized myocardial involvement.

Measurement of dynamic deformation during shock loading using a fiber-optic loop-sensor

Abstract Characterizing materials under shock loading has been of interest in fields such as protective material development, biomechanics to study the injury mechanics and high-speed aerodynamic structures. However, shock loading of material is a very short duration phenomenon and it is extremely challenging to develop sensors for dynamic measurements under such loading conditions. Optical fiber sensors that present the possibilities to allow high resolution measurement of force or displacement in such high strain rate loading conditions. This work studies the possibility of developing a single mode optical fiber sensor based on the principle of power losses from the curved section for dynamic measurements under shock loading conditions. The strain measurement results obtained from the optical sensors are validated with the controlled digital image correlation measurements are found to be in close correlation. The sensor was able to provide time sensitivity of better than 1 ms. The results show that the fiber sensor has the characteristics of high sensitivity and high precision, which can be used to measure fine vibration in real-time.

Veneer-wrapped steel columns: Proof-of-concept experimental and numerical investigations

This paper presents and discusses the structural behaviour of a novel type of steel–timber composite column to be used in residential building applications. It consists of a circular hollow section wrapped by multiple beech veneer sheets and where the composite action is ensured by a structural bi-component glue applied over the contact surfaces. As part of a proof-of-concept study, five short and three long columns with lengths of 0.27 m and 2.00 m, respectively, were tested under vertical concentric load with fibres parallel to the load direction and inclined by 15°. The global response of the specimens in terms of load-displacement behaviour and failure modes was studied, along with localised strain measurements through strain gauges and a digital image correlation (DIC) system. Results showed a significant increase in buckling resistance due to the stiffness added by the veneer layers. Already with the still-moderate veneer layer thicknesses used in this study, an increase in strength of over 25 % could thus be achieved. This enhancement highlights the effectiveness of veneer wrapping in stabilizing the inner core and delaying the occurrence of flexural buckling failure. A 3D non-linear finite element model (FEM) validated these findings, showing a good correlation with experimental results in resistance and stiffness. A parametric study was conducted to explore different geometries and materials, thus creating an extended FEM-based database. A relatively good agreement with modest deviation between the FEM predictions and analytical formulations available in the European Standards was found, considering the appropriate introduction of the mechanical properties of timber.

Integrated all-fiber-optic sensor based on FPI and MZI composite structures for temperature and strain measurement

In this paper, a temperature and strain sensor based on fiber-optic Mach-Zehnder interferometer (MZI) cascaded with Fabry-Perot interferometer (FPI) is designed and fabricated. The integrated sensor structure consists of no-core fiber (NCF) sandwiched by two sections of multi-mode fiber (MMF), hollow-core fiber (HCF), and two single-mode fibers (SMF) which are cascaded at the ends of the MMF and the HCF. Due to the thermal expansion effect, thermo-optic and elasto-optic effects of fiber material, the increase of the temperature and strain will make the change of the transmission mode, which will cause the spectral fringes wavelength shifting with strain, and the intensity of the spectral fringes varying with temperature but not strain variations in multiple temperature ranges. The series experiments valid show that the sensor with integrated structure realizes the strain and temperature measurements in multiple temperature ranges, and the minimum and maximum temperature sensitivities are -0.278dBm/°C and -0.670dBm/°C in the temperature range of 68-86 °C and 123-141 °C, respectively. The strain sensitivity is 2.17pm/με all over the measured range. The integrated sensor structure has the advantages of high sensitivity, multiple measuring ranges, simple manufacturing, and low cost, which has the potential to be applied in the field of the internal strain and temperature measurements of different structures.

EXPERIMENTAL ANALYSIS OF POISSON RATIO ON METAMATERIALS MANUFACTURED FROM CRUMPLED ALUMINUM FOIL SUBJECTED TO UNIAXIAL COMPRESSION

In this work experimental results are presented concerning the auxetic behavior of a crumpled metamaterial manufactured with aluminum foil, so far such experimental evidence has not been reported by other authors. Thus, 2D digital image correlation (DIC) was used to make full field measurements of longitudinal and transverse strains on the surface of crumpled aluminum specimens under axial compression; it was no possible to use conventional methods on the measurements of strains, such as strain gages or extensometers, due to the irregular topography on the surface of the specimens. The obtained results exhibit the auxetic nature of the aluminum crumpled material, with Poisson´s ratio values that vary from ?=-0.17 to ?=-0.02 for relative densities in the range ?_r=0.07 to ?_r=0.21. Keywords: Auxetic, Digital Image Correlation, Crumpled material, Poisson, Computer vision system.

Cascaded Fabry-Perot cavity and fiber Bragg grating on sapphire fibers for high-temperature strain sensing

High-temperature strain sensors are key elements for several applications. Key issues of the existing devices include the difficulties of sensor operating above 1000°C as well as the very strong thermal effect under high temperatures introducing significant bias on the strain measurement. Here we developed a cascaded Fabry-Perot cavity and fiber Bragg grating strain sensor fully integrated on sapphire fibers, permitting a sufficient temperature compensation and strain measurement up to 1150°C temperature. A three-point adhesive bonding process is proposed to greatly improve the adhesion performance, and hence the robustness of the device at high temperatures. Experimental results show that the fabricated strain sensor can achieve a measurement range of ±1000 με at temperature up to 1150°C. The experimental results show that the measurement accuracy is not more than 5% at room temperature. the measurement accuracy is significantly decreased at high temperature, and the maximum strain measurement error is 14% at 1150°C.

Associations Between Body Mass Index, Gait Biomechanics, and In Vivo Cartilage Function After Exercise in Those With Anterior Cruciate Ligament Reconstruction

Background: Both high body mass index (BMI) and anterior cruciate ligament reconstruction (ACLR) independently influence knee osteoarthritis risk. Preliminary evidence shows the combination of these risk factors leads to poorer recovery and altered biomechanical outcomes after ACLR, but few studies have directly evaluated early changes in cartilage health between normal-BMI and high-BMI groups in this population. Purpose: To evaluate ultrasound-based measures of cartilage strain and compositional changes (via echo-intensity [EI]) in response to an incline walking stress test between normal-BMI and high-BMI individuals with ACLR. A secondary evaluation was conducted of associations between habitual walking biomechanics (ie, ground-reaction forces, sagittal knee kinetics and kinematics) and cartilage strain and EI outcomes. Study Design: Controlled laboratory study. Methods: Gait biomechanics and femoral trochlear ultrasound analyses were evaluated in 64 participants with ACLR who had normal BMI (BMI < 27.0; n = 40) and high BMI (BMI ≥ 27.0; n = 24). Ultrasound images were collected bilaterally before and after an incline treadmill walk, and medial and lateral trochlear strain and EI changes pre-post exercise were used to compare BMI groups and limbs. Gait outcomes included ground-reaction forces, peak sagittal plane knee moments, angles, and excursions and were used to determine associations with cartilage outcomes in the entire cohort. Results: High-BMI individuals with ACLR exhibited greater medial trochlear cartilage strain in the ACLR limb compared with normal-BMI individuals (approximately 6%; P < .01). In those with high BMI, the ACLR limb exhibited greater medial trochlear strain relative to non-ACLR limbs (approximately 4%; P < .05), but between-limb differences were not observed in the normal-BMI group (P > .05). Medial trochlear EI changes were greater bilaterally in those with high BMI compared with normal-BMI ACLR counterparts (approximately 10%; P < .01). Last, individuals who walked with greater peak knee flexion angles exhibited less medial cartilage strain (ΔR2 = 0.06; P = .025). Conclusion: The data suggested that high BMI affects cartilage functional properties after ACLR, whereas smaller knee flexion angles were associated with larger medial cartilage strain. Clinical Relevance: High-BMI individuals with ACLR may represent a subset of patients exhibiting earlier declines in cartilage functional integrity in response to loading, necessitating additional or more targeted interventions to mitigate disease development.

3D printed feathers with embedded aerodynamic sensing

Bird flight is often characterized by outstanding aerodynamic efficiency, agility and adaptivity in dynamic conditions. Feathers play an integral role in facilitating these aspects of performance, and the benefits feathers provide largely derive from their intricate and hierarchical structures. Although research has been attempted on developing membrane-type artificial feathers for bio-inspired aircraft and micro air vehicles (MAVs), fabricating anatomically accurate artificial feathers to fully exploit the advantages of feathers has not been achieved. Here, we present our 3D printed artificial feathers consisting of hierarchical vane structures with feature dimensions spanning from 10-2to 102mm, which have remarkable structural, mechanical and aerodynamic resemblance to natural feathers. The multi-step, multi-scale 3D printing process used in this work can provide scalability for the fabrication of artificial feathers tailored to the specific size requirements of aircraft wings. Moreover, we provide the printed feathers with embedded aerodynamic sensing ability through the integration of customized piezoresistive and piezoelectric transducers for strain and vibration measurements, respectively. Hence, the 3D printed feather transducers combine the aerodynamic advantages from the hierarchical feather structure design with additional aerodynamic sensing capabilities, which can be utilized in future biomechanical studies on birds and can contribute to advancements in high-performance adaptive MAVs.

Prediction of residual stresses in additively manufactured parts using lumped capacitance and classical lamination theory

Several industries are interested in Laser Powder Bed Fusion (L-PBF) Additively Manufactured (AM) metal parts because their designs can be made arbitrarily complex while retaining bulk-type material properties. However, the residual stresses (RS) and distortions caused by the heat gradients inherent to L-PBF processes are detrimental to the structural integrity of the parts and must be taken into consideration during the part design cycle. Predicting the state of stresses in as-built 3D printed parts is a difficult problem that is typically approached with the use of transient thermomechanical Finite Element Models (FEMs). However, the nonlinearities associated with AM processes are difficult to capture in these FEMs without increasing the computational cost of the simulation, limiting their ability to be incorporated into practical design cycles. This work presents a novel analytical framework that combines lumped capacitance nonlinear heat transfer with time dependent classical lamination theory to efficiently and accurately predict RS in as-built L-PBF parts without the need of FEMs. The simulation was compared to Neutron Diffraction (ND) residual strain measurements taken at Oak Ridge National Laboratories (ORNL) as well as Synchrotron X-ray Diffraction (XRD) strain data published by the National Institute of Standards and Technology (NIST). The simulation predictions and the experimental data showed excellent agreement for the in-plane strain directions, and general agreement for the out of plane strain component, highlighting an area where further development can be implemented.