Deflection Slope Research Articles

Self-buckling with initial imperfections: Application to trees

In most structural systems, initial imperfections, such as initial deflection, is an unavoidable challenge, and it significantly influences buckling. This study aimed to theoretically explain the effect of initial deflection and initial slope on self-buckling characteristics of heavy columns subjected to self-weight. Specifically, we examined cantilevers composed of isotropic material with a constant cross-section. Accounting for both self-weight and axial compression load, we developed a formula characterizing the self-buckling problem for some simplified cases such as sin-curve, hypergeometric curve, and straight line (initial slope). Consequently, we established the relationship between the self-buckling characteristics and the level of initial imperfections. We discovered that the greatest height for self-weight buckling is proportional to the 2/3 power of radius, regardless of the initial imperfection. Moreover, our findings suggest the potential to predict the height of tree-like natural structures using the greatest height formula and considering initial imperfections.

Buckling Assessment in the Dynamics Mechanisms, Stewart Platform Case Study: In the Context of Loads and Joints, Deflection Positions Gradient

This study introduces an approach for modeling an arm of a Stewart platform to analyze the location of sections with a high deflection among the arms. Given the dynamic nature of the Stewart platform, its arms experience static and dynamic loads. The static loads originate from the platform’s own weight components, while the dynamic loads arise from the movement or holding of equipment in a specific position using the end-effector. These loads are distributed among the platform arms. The arm encompasses various design categories, including spring-mass, spring-mass-damper, mass-actuator, and spring-mass-actuator. In accordance with these designs, joint points should be strategically placed away from critical sections where maximum buckling or deformation is prominent. The current study presents a novel model employing Euler’s formula, a fundamental concept in buckling analysis, to propose this approach. The results align with experimental and numerical reports in the literature that prove the internal force of the platform arm is affecting the arm stiffness. The equal stiffness of an arm is related to its internal force and its deflection. The study demonstrates how higher levels of dynamic loading influence the dynamic platform, causing variations in the maximum arm’s buckling deflection, its precise location, and the associated deflection slope. Notably, in platform arms capable of adjusting their tilt angles relative to the vertical axis, the angle of inclination directly correlates with deflection and its gradient. The assumption of linearity in Euler’s formula seems to reveal distinctive behavior in deflection gradients concerning dynamic mechanisms.

A novel practical algorithm using machine learning to differentiate outflow tract ventricular arrhythmia origins.

Diagnosis of outflow tract ventricular arrhythmia (OTVA) localization by an electrocardiographic complex is key to successful catheter ablation for OTVA. However, diagnosing the origin of OTVA with a precordial transition in lead V3 (V3TZ) is challenging. This study aimed to create the best practical electrocardiogramalgorithm to differentiate the left ventricular outflow tract (LVOT) from the right ventricular outflow tract (RVOT) of OTVA origin with V3TZ using machine learning. Of 498 consecutive patients undergoing catheter ablation for OTVA, we included 104 patients who underwent ablation for OTVA with V3TZ and identified the origin of LVOT (n = 62) and RVOT (n = 42) from the results. We analyzed the standard 12-lead electrocardiogram preoperatively and measured 128 elements in each case. The study population was randomly divided into training group (70%) and testing group (30%), and decision tree analysis was performed using the measured elements as features. The performance of the algorithm created in the training group was verified in the testing group. Four measurements were identified as important features: the aVF/II R-wave ratio, the V2S/V3R index, the QRS amplitude in lead V3, and the R-wave deflection slope in lead V3. Among them, the aVF/II R-wave ratio and the V2S/V3R index had a particularly strong influence on the algorithm. The performance of this algorithm was extremely high, with an accuracy of 94.4%, precision of 91.5%, recall of 100%, and an F1-score of 0.96. The novel algorithm created using machine learning is useful in diagnosing the origin of OTVA with V3TZ.

Self-healing behaviors and its effectiveness evaluations of fiber reinforced shape memory polyurethane/SBS modified asphalt mortar

To further understand self-healing behaviors of cracks in fiber reinforced asphalt mortar, shape memory polyurethane/styrene butadiene styrene modified asphalt mortar (PSAM) was first prepared. Then shape memory properties of lignin fiber reinforced PSAM (LFAM) and polyester fiber reinforced PSAM (PFAM) were characterized. The effects of filler-asphalt ratio and fiber type on the multi-cycle self-healing results of LFAM and PFAM were discussed. The self-healing effectivenesses in each crack-healing cycle and whole multi-cycle self-healing process were evaluated. Results indicate that shape memory properties of LFAM and PFAM are lowered as their filler-asphalt ratios are increased. LFAM and PFAM show satisfactory shape memory properties, but PFAM has better shape memory performance than LFAM, and its higher shape recovery force further improves its self-healing effectivenesses. Also, when the filler-asphalt ratio is raised, both creep deflection and creep slope of LFAM and PFAM are decreased, but their creep stiffnesses are increased. The self-healing mostly restores the mechanical properties of LFAM and PFAM. PFAM shows higher low-temperature crack resistance than LFAM. Meanwhile, the creep deflection and creep slope of PFAM are higher than those of LFAM as the filler-asphalt ratio is the same one, while the creep stiffness of PFAM is smaller than that of LFAM. LFAM shows a brittle failure at low temperature, but PFAM shows a flexible failure. Additionally, the self-healing effectiveness of LFAM and PFAM in each crack-healing cycle is decreased as the crack-healing cycle is increased. Finally, PFAM shows a higher self-healing rate than LFAM. The mechanical and self-healing characteristics of PFAM are more stable than those of LFAM. The multi-cycle self-healing test indexes can assess the multi-cycle self-healing effectiveness of LFAM and PFAM.

Evaluating structural characteristics of asphalt pavements by using deflection slopes from traffic speed deflectometer

The Traffic Speed Deflectometer (TSD) overcomes the limitations of the Falling Weight Deflectometer (FWD) in terms of traffic interruption and testing inefficiency, making it an efficient tool for network-level pavement structural evaluation. The current research on TSD is inherited from FWD and mainly focuses on deflection itself. However, the raw measurement of TSD is the deflection slope, i.e., the first-order derivative of deflection. TSD deflection is calculated by curve fitting and integration, and the extensive use of deflection itself may accumulate the error caused by curve fitting. This study explores the potential use of TSD deflection slope in assessing the strength of pavement structures, estimating the location of the inflection point, and calculating the lag distance. The results show that both the TSD deflection and slope are effective in detecting weak asphalt layers and subgrades, but they are not sensitive to damage to the base layer. It is recommended that TSD slopes at 5″ and 60″ (in front of the load center) be used to indicate the strength of the asphalt layer and subgrade, respectively. The location of the inflection point is related to the asphalt thickness and subgrade modulus, and it can be approximated by the location of the maximum slope measurement. In addition, the lag distance can be calculated by determining the maximum deflection point or by determining the zero-slope point. Since the maximum deflection method accumulates errors in curve-fitting and is more sensitive to interpolation methods, the zero-slope method is recommended to calculate the lag distance.

An dynamical evaluation of size-dependent weakened nano-beam based on the nonlocal strain gradient theory

This paper examines the free lateral vibration of a cracked nano-beam based on Euler-Bernoulli beam theory and nonlocal strain gradient theory (NSGT). Due to the importance and application of nanostructures, their mechanical and mechanical properties are essential. The governing equations and boundary conditions related to using the Hamilton principle have been extracted. The beam separation with the nano-beams division into two parts attached to the Torsion spring is modeled. The model calls the excess strain energy due to crack and increases the discontinuity in the deflection slope. This study investigated the effects of crack propagation, crack intensity, material length scale parameter, and various nonlocal parameters. A comparison of previous studies has been published, where a good agreement is observed. The results show that the parameters mentioned above play an important role in dynamical behavior.

On the TSD deflection velocity measurements: a revision to the current state of the art and discussion over its applicability for concrete pavement assessment

ABSTRACT The fourth-generation TSD can provide pavement deflection data at a much higher rate than previous versions. This data is valuable to evaluate the structural health of the transverse joints in concrete pavements. Analysis of TSD measurements from a jointed pavement segment allowed the detection of a mistake in the way the TSD's deflection velocity [vy] data is processed to get deflection slope [S] estimates: We state and prove that the well-known direct relationship between vy and S is only valid in limited scenarios, and particularly invalid nearby the transverse joints. We highlight that vy is made up of two components, one of which is related to S and that at the vicinity of a discontinuity in the pavement structure, the second component of vy gains relevance and explains the discrepancy between vy and S. Also, it is shown that TSD vy measurements gathered near a joint resemble vy signals simulated with a linear elastic model. Thus, this study brings new insight into the contents of a TSD vy measurement and buttresses the TSD’s reliability as a vy measurement device. Plus, it suggests that further research should develop TSD data interpretation schemes based on vy instead of deflection slopes and depths.

Free transverse vibrations analysis of size-dependent cracked piezoelectric nano-beam based on the strain gradient theory under mechanic-electro forces

This paper investigates the free lateral vibration of a cracked nano-beam to piezoelectric effects on Euler-Bernoulli beam theory and nonlocal strain gradient theory (NSGT). So far, the propagation and growth of cracks in nano-beams have not been done by modeling the crack area using torsion springs using NSGT. This article investigates the free vibrations of cracked nano-beams using piezoelectric effects. The governing equations, related boundary conditions, and piezoelectric effects were derived using the Hamilton principle. Nano-beam separation is modeled by splitting nanoparticles into two parts connected to a rotating spring. The model calls the extra strain energy due to cracking and increases the discontinuity in the deflection slope. This study investigates the effects of crack propagation, crack intensity, piezoelectric effects, longitudinal scale parameter, and nonlocal parameter. A comparison of previous studies has been published in which a good agreement is observed. The results show that the mentioned parameters play an important role in dynamic behavior.

Anatomy-based characteristics of far-field SVC electrograms in right superior pulmonary veins after isolation

Background. Far-field electrograms from superior vena cava (SVC) can be present in right superior pulmonary vein (RSPV) after pulmonary vein (PV) isolation. Objectives. To analyze the characteristics of far-field SVC potentials in RSPV after PV isolation and the local anatomy difference between patients with and without the potentials. Methods. Patients undergoing PV isolation were retrospectively reviewed, contrast-enhanced computed tomography (CT) was performed before procedure for observing the anatomical relationship between RSPV and SVC. The prevalence and characteristics of far-field SVC electrograms were described and compared to far-field left atrial potentials at the nearest point along the linear ablation lesion. The anatomical proximity of RSPV and SVC on a 2-dimensional horizontal CT view was compared between patients with and without far-field SVC potentials. Results. Far-field SVC electrograms were observed in 35/92(38%) patients with an amplitude of 0.24 ± 0.11 mV and a major deflection slope of 0.051 ± 0.036 mV, both significantly higher than far-field left atrial electrograms (p < .001). In patients with far-field SVC electrograms, 83% had connected RSPV-SVC, defined as distance between RSPV and SVC endocardium less than 3 mm at the layer of RSPV ostium roof, while in patients without far-field SVC electrograms, 70% had disconnected RSPV-SVC. Conclusions. Far-field SVC electrograms appeared in RSPV had a prevalence higher than previously reported and a sharper major deflection compared to far-field left atrial electrograms. Connected RSPV-SVC on CT was associated with the presence of far-field SVC electrograms.

On the Appropriate Rotary Inertia in Timoshenko Beam Theory

The rotary inertia defined by Timoshenko to account for the angular velocity effect in flexural vibration of beams has been questioned by some researchers in recent years, and it caused some confusions. This paper discusses the appropriate rotary inertia in Timoshenko beam theory (TBT) and evaluates the influence of the two forms of the rotary inertia on the prediction of the higher-mode frequencies of transversely vibrating beams. Based on the theory of elasticity and variational principle, this work shows that the rotary inertia in the original TBT, defined in terms of the rotation of beam cross-section induced by bending deformation, is variational consistent and is capable of yielding good results of the phase velocities of transversely vibrating beams even in the case where the wavelength of vibrating beams approaches the beam height. On the other hand, the so-called corrected TBT, in which the rotary inertia is defined in terms of the slope of beam deflection, is neither variational consistent nor accurate when the wavelength of vibrating beams approaches the beam height. Therefore, the rotary inertia in TBT defined by Timoshenko is correct and should be used in the dynamic analysis of beams.

Effects of vacuum exposure on mechanical properties of thermoplastic materials

The present paper proposes the study of the behavior of three thermoplastic materials: acrylonitrile butadiene styrene (ABS), poly(lactic acid) (PLA), and polyethylene glycol terephthalate (PETG), processed by additive manufacturing type fused deposition modelling (FDM) when exposed to low vacuum. The experiment was composed of three moments consisting of tridimensional modeling and manufacturing of the specimens, drying process and vacuum exposure for 24 hours, according to American Society for Testing and Materials (ASTM) D6653/D6653M standards, and bending test for the determination of mechanical properties, based on ASTM D790 standards. The vacuum chamber tests exposed oscillations in the pressure indicating gases releasing from the specimen, but none of the samples showed visible deformations. Subjecting the materials exposed to low vacuum to bending tests and comparing them to the unexposed material, we observed a significant increase in the calculated modulus of elasticity and a change in the slope of graphic force versus deflection in all materials. This behavior demonstrates that it is possible to submit polymeric materials to vacuum, and low vacuum exposure can be a treatment for thermoplastic materials. In the future, a study using a spectrometer will be necessary to verify which gases are present during pressure oscillation in the chamber, thus making it possible to understand which factor has increased the mechanical properties of the materials. In sequence, experiments will be necessary to validate the vacuum exposure as a form of treatment of materials and to verify the possibility of applying thermoplastics commonly used in additive manufacturing for low-impact space applications.

Effects of vacuum exposure on mechanical properties of thermoplastic materials

The present paper proposes the study of the behavior of three thermoplastic materials: acrylonitrile butadiene styrene (ABS), poly(lactic acid) (PLA), and polyethylene glycol terephthalate (PETG), processed by additive manufacturing type fused deposition modelling (FDM) when exposed to low vacuum. The experiment was composed of three moments consisting of tridimensional modeling and manufacturing of the specimens, drying process and vacuum exposure for 24 hours, according to American Society for Testing and Materials (ASTM) D6653/D6653M standards, and bending test for the determination of mechanical properties, based on ASTM D790 standards. The vacuum chamber tests exposed oscillations in the pressure indicating gases releasing from the specimen, but none of the samples showed visible deformations. Subjecting the materials exposed to low vacuum to bending tests and comparing them to the unexposed material, we observed a significant increase in the calculated modulus of elasticity and a change in the slope of graphic force versus deflection in all materials. This behavior demonstrates that it is possible to submit polymeric materials to vacuum, and low vacuum exposure can be a treatment for thermoplastic materials. In the future, a study using a spectrometer will be necessary to verify which gases are present during pressure oscillation in the chamber, thus making it possible to understand which factor has increased the mechanical properties of the materials. In sequence, experiments will be necessary to validate the vacuum exposure as a form of treatment of materials and to verify the possibility of applying thermoplastics commonly used in additive manufacturing for low-impact space applications.

Method for Direct Measurement of Structural Rolling Resistance for Heavy Vehicles

In this paper, a new in situ method for determining the structural rolling resistance (SRR), defined as the dissipated energy caused by deformation of the pavement when subjected to a moving load, is presented. The method is based on the relation between SRR and the slope of the deflection basin under a moving load. Using the Traffic Speed Deflectometer, the deflection slope is measured at several positions behind and in front of the right rear-end tire pair of a full-size truck trailer while driving under realistic conditions. The deflection slope directly under the tire is estimated from a linear interpolation between the two nearest sensors. A set of data from a test road segment located in Denmark is analyzed and the SRR coefficients are found to be in the range 0.005% to 0.05%. The deflection slope measurements have a high reproducibility (repeated measurements agree within standard deviations of 4% to 10%) with high spatial resolution, and the method for calculating SRR from these measurements has the clear advantage that it requires no knowledge or model of the pavement structure or viscoelastic properties. Numerical simulations of pavement response show that the proposed interpolation method tends to underestimate the actual SRR, and better estimates can be obtained by other interpolation schemes.

Impact-induced flexural response of axially loaded uniform Timoshenko beams with non-classical ends: a sensitivity study of the dynamic load factor

A dynamic analysis of axially loaded Timoshenko beams with intermediate fixities is presented. The underwater part of a craft is modeled as a flexible beam, which rises out and slams against the water at a large vertical velocity, causing highly localized hydrodynamic impact pressure moving at high velocities across the beam, setting it into high-frequency vibrations. The beam natural frequencies depend on the slenderness ratio, axial load, end fixities, and structural damping. The natural frequencies and modeshapes (for total deflection and pure bending slope) are generated through Eigen analysis. Next, normal mode summation is used to analyze the impact-induced vibration response, which is generated for various impact speeds, deadrise angles, end fixities, and axial loads, of the beam. A parametric study is done to predict the maximum dynamic stresses on the structure. The sensitivity of the dynamic load factor (DLF) is studied with respect to the above parameter space. Conclusions are drawn leading to insights into sound structural designs.

Extracting information from the shape and spatial distribution of evoked potentials

BackgroundOver 90 years after its first recording, scalp electroencephalography (EEG) remains one of the most widely used techniques in human neuroscience research, in particular for the study of event-related potentials (ERPs). However, because of its low signal-to-noise ratio, extracting useful information from these signals continues to be a hard-technical challenge. Many studies focus on simple properties of the ERPs such as peaks, latencies, and slopes of signal deflections. New methodTo overcome these limitations, we developed the Wavelet-Information method which uses wavelet decomposition, information theory, and a quantification based on single-trial decoding performance to extract information from evoked responses. ResultsUsing simulations and real data from four experiments, we show that the proposed approach outperforms standard supervised analyses based on peak amplitude estimation. Moreover, the method can extract information using the raw data from all recorded channels using no a priori knowledge or pre-processing steps. Comparison with existing method(s)We show that traditional approaches often disregard important features of the signal such as the shape of EEG waveforms. Also, other approaches often require some form of a priori knowledge for feature selection and lead to problems of multiple comparisons. ConclusionsThis approach offers a new and complementary framework to design experiments that go beyond the traditional analyses of ERPs. Potentially, it allows a wide usage beyond basic research; such as for clinical diagnosis, brain-machine interfaces, and neurofeedback applications requiring single-trial analyses.

A modified Kirchhoff plate theory for analyzing thermo-mechanical static and buckling responses of functionally graded material plates

In this paper, we present a modified Kirchhoff theory for analyzing thermo-mechanical static and buckling responses of functionally graded material (FGM) isotropic and sandwich plates. In comparison to the classical Kirchhoff theory, the proposed method is taken account into the shear deformation effects, then it can be applied for both moderately thick and thin plates. On the other hand, comparing to the first order shear deformation theory (FSDT) or Reissner-Mindlin plate theory, the number of independent unknowns reduces one variable and retains four degrees of freedom (Dofs) per node. The shear locking phenomenon is also negligible due to extending from the classical Kirchhoff theory. Furthermore, a new normalization of a quartic form is used to build the shape functions in the radial point interpolation method (RPIM). The novel imposing essential boundary conditions related to slopes of deflections has been proposed, then the enforcement of these gradient deflections becomes easily and directly as the same in finite element analysis. The obtained numerical results for the thermo-mechanical static and buckling problems from the proposed method are stable and well accurate prediction as comparing to the exact solutions and other published analyses.

Estimating “True” Variability of Traffic Speed Deflectometer Deflection Slope Measurements

AbstractIn this paper, the difference sequence method is used to decompose traffic speed deflectometer (TSD) deflection slope measurements variability into “true” spatial variability that is due to pavement structural changes and noise variability. A robust method to evaluate the noise standard deviation is presented and the difference sequence method is validated using simulated examples. The difference sequence method is then used to calculate the noise standard deviation and “true” spatial variability of TSD deflection slope measurements. The evaluated noise standard deviation is also used to determine the optimal smoothing of TSD deflection slope measurements using an unbiased measure of the risk. This method is compared with the generalized cross validation (GCV) criterion to determine the optimal smoothing. Results suggest the unbiased risk criterion performs better than the GCV criterion. This gives an objective method, which is currently lacking, to average TSD measurements, and more generally any...

Prediction of thermally-controlled actuation for shape memory alloy film-based bimorph cantilevers

A model is proposed for predicting the deflection of bimorph cantilevers made of a shape memory alloy film deposited onto solid substrates, by taking into account the changes in the thermal and elastic properties of the film during the martensitic phase transformation. The zero actuation reference temperature is the deposition or annealing temperature, with the film in the austenite phase. On cooling from this point, the thermoelastic stress building up in the bimorph causes bimetal-type behavior until the onset of the austenite–martensite transformation, which now controls the actuation up to its completion, when the bimetal actuation reappears. By adapting the classical bimetal thermostat model to the case when one component undergoes martensitic transformation, the deflection during heating and cooling is calculated by averaging the isostrain and isostress phase distribution bounding approximations; the case of a Ti50.1Ni49.9 film/Si was examined. Predictions in good agreement with the recorded deflection of a Ti49.2Ni50.8/Si cantilever (up to a temperature shift explained by composition change and stress developed in the film during the transformation) resulted, indicating a strong effect (attributed to the differences between the elastic and thermal constants of the two phases) of the martensitic phase transformation on the deflection slope and sign.

Wavelet Denoising of TSD Deflection Slope Measurements for Improved Pavement Structural Evaluation

AbstractContinuous deflection devices (CDDs) can safely measure pavement deflection (or other related properties) while traveling at highway speed, which reduces traffic disruption. CDD measurements are contaminated with relatively high noise levels compared to stop‐and‐go devices such as the Falling Weight Deflectometer. In this article, we use wavelet transform denoising to remove the noise and estimate the true deflection slope measurements obtained from the Traffic Speed Deflectometer. Results show that failure to denoise deflection slope measurements can lead to calculated Effective Structural Number values that are highly variable (unstable). Attempting to filter these highly variable measurements can lead to erroneous results. We also use wavelet transform denoising to identify localized weak spots such as those that are caused by pavement reflection cracking. Identifying weak spots with wavelets is possible because wavelets are spatially adaptive to local features. In contrast, a linear filter is not capable of adapting to local features.

Limits of agreement method for comparing TSD and FWD measurements

This article uses the limits of agreement (LOA) method to compare the falling weight deflectometer (FWD) and the traffic speed deflectometer (TSD), two pavement structural evaluation devices. The TSD measures deflection slope, whereas the FWD measures deflection. For this reason, measurements were converted to the surface curvature index (SCI) and the base damage index (BDI), which can be obtained from each device. The SCI and BDI agreement between the two devices was then evaluated. Although the relationship between the calculated SCI and BDI using both equipments is reasonably close to the line of equality, there is a significant variation and a bias in this relationship. For example, for an average SCI or BDI value of 300 μm, the bias was 30 μm (FWD values lower than TSD values), and the LOA was 380 μm.