Measured Strain Data Research Articles

Empirical Analysis of the Impact Strength of Textile Knitted Barrier Meshes

Abstract The assumptions of instrumental methodology for measuring dynamic loads of knitted barrier meshes were defined. A test stand was built, original in terms of both mechanical construction and electronic measuring system, connected to a computer data analysis system. Maximum values of dynamic forces in the mesh fastening strings were determined. The correctness of the strain gauges construction and measurement data transmission systems was confirmed. Tests of multidirectional resistance to dynamic loads in the mesh fastening strings were carried out. The experiment involved dropping a ball with a mass of 5 kg and a diameter of 10 cm, from a height of 1 m and 2 m onto the mesh surface. The potential impact energy equaled Ep1 = 49.05 J and Ep2 = 98.1 J. The tests showed that the highest force values were observed for meshes with square-shaped a-jour structure, and for mesh with diamond-shaped a-jour geometry the force values were lower. A symmetrical forces distribution was observed in all the strings. The highest forces were recorded in the middle strings and the lowest in the outer ones. The conducted tests confirmed the correctness of the adopted constructional solutions of test stand for identification of dynamic stress distribution in mesh fastening strings. The developed method is a useful verification tool for numerical analysis of mechanical properties of barrier meshes.

Shape Sensing of Plate Structures Using the Inverse Finite Element Method: Investigation of Efficient Strain–Sensor Patterns

Methods for real-time reconstruction of structural displacements using measured strain data is an area of active research due to its potential application for Structural Health Monitoring (SHM) and morphing structure control. The inverse Finite Element Method (iFEM) has been shown to be well suited for the full-field reconstruction of displacements, strains, and stresses of structures instrumented with discrete or continuous strain sensors. In practical applications, where the available number of sensors may be limited, the number and sensor positions constitute the key parameters. Understanding changes in the reconstruction quality with respect to sensor position is generally difficult and is the aim of the present work. This paper attempts to supplement the current iFEM modeling knowledge through a rigorous evaluation of several strain–sensor patterns for shape sensing of a rectangular plate. Line plots along various sections of the plate are used to assess the reconstruction quality near and far away from strain sensors, and the nodal displacements are studied as the sensor density increases. The numerical results clearly demonstrate the effectiveness of the strain sensors distributed along the plate boundary for reconstructing relatively simple displacement patterns, and highlight the potential of cross-diagonal strain–sensor patterns to improve the displacement reconstruction of more complex deformation patterns.

Design optimization focused on failures during developmental testing of the fabricated rear-axle housing

In the development of fabricated rear axle housing for heavy-duty off-road applications, engineering against failures was challenging due to budget and timeline limitations. Rear-axle housing failure on the road is a threat to other road users and hence zero failures targeted in the design verification phase. The analysis of rear axle housing beam failures had been well established. Failure in Torture-Track (TT) was resolved by engineering against the stress concentration at the notch, by adding inner side weld at the central section of the axle. This optimized design got verified in FEA and Rig testing for maximum stress concentration reduction and fatigue life improvement, respectively. The optimized design completed the target mileage in TT successfully. Further strengthening of the central section resulted in the failure mode shift from the central section to the beam section (proved in Rig testing). Hence, reestimated the life of rear-axles based on new strain measurement in severe operation. The strain measurement data from off-road testing of the design prototype closer to real-world application gave more accurate stress concentration results. It became the critical influencer to reduce further design iterations based on failures observed during design verifications in the new product development process.

Distributed Dynamic Load Identification on Irregular Planar Structures Using Subregion Interpolation

Spatially distributed load on aircraft structures is difficult to obtain due to the limitation of measurement technology, the complexity of load and the external environment of the aircraft during flight, etc. A load identification method based on a subregion interpolation technique is proposed to indirectly estimate the distributed dynamic load from measured strain data on planar structures. The load distribution area is discretized into several subregions and the load distribution function in each subregion is represented by a set of local interpolation functions multiplied by their corresponding coefficients. A modified Green’s function matrix is formulated to establish the relationship between the local distributed dynamic load in the domain composed of the subregions sharing the same node and the structural response data. Hence, both the load’s distribution and time histories can be identified from structural response by solving the new formulated inverse problem. Numerical simulations on a flat cantilever plate and a planar structure with irregular geometry are conducted to show the effectiveness of the proposed method. Results show that the proposed method has better adaptability on the types of load distribution and structural configurations than the existing methods.

Development and experimental verification of an adaptive structure for phased antenna array using SMA bunch

An adaptive structure for a phased antenna array is proposed using shape memory alloy (SMA) as an actuation component for the plate flatness control. Fiber Bragg Grating (FBG) sensors are designed for plate strain measurement, and a strain displacement transformation method is introduced to obtain the deformation field from the strain measurement data. The deformation field is then used to determine the correction loads of actuation points using integer nonlinear programming analysis. An adaptive prototype for the phased antenna array plate is developed with the distribution of monitored, actuation, and load points. Numerical simulations are performed to demonstrate the detailed process of the strain displacement transformation method. Moreover, the method is further discussed after testing the adaptive plate structure with the digital image correlation (DIC) technology. Finally, the reliability and efficiency of the proposed active control scheme are validated with an experimental setup. The study promotes the engineering application of the active control concept in large scale phased antenna arrays.

Stressing State Analysis of Reinforcement Concrete Beams Strengthened with Carbon Fiber Reinforced Plastic

This paper investigated the working behavior characteristics of six reinforcement concrete (RC) beams subjected to bending based on the numerical shape function (NSF) method and structural stressing state theory. Firstly, the structural stressing state mode is expressed based on the generalized strain energy density (GSED) derived from the measured strain data. Then, one of the Carbon Fiber Reinforced Plastic (CFRP)-strengthened RC beams is taken as an example and the leap characteristics of RC beam’s stressing state are detected by applying the Mann–Kendall (M–K) criterion, updating the existing definition of the structural failure load. Accordingly, the stressing state modes and strain fields of the CFRP-strengthened RC beam are proposed to reveal their leap characteristics. Furthermore, through comparing the working performance of six RC beams, the effects of different strengths and different reinforcement ratios on CFRP strengthening performance are investigated. Finally, the NSF method is applied to reasonably interpolate the limited strain data for further revealing the stressing state characteristics of the RC beams. The research results explore a new analysis method to conduct an accurate estimation of the structural failure load and provide a reference for the future design of CFRP-strengthened RC beams.

Establishment of Myocardial Strain Measurement Data in Pediatric Patients Without Structural Heart Disease: A Single Center Study.

Accurate assessment of LV systolic function remains a challenge, especially in the pediatric population. Myocardial strain measurement by 2D speckle tracking echocardiography (2DSTE) is a relatively new modality for assessment of regional and global myocardial wall motion. This study aims to establish the normative value among various pediatric age groups at a large pediatric tertiary care institution and to describe the challenges encountered in establishing such strain data. Transthoracic echocardiograms were acquired in 121 healthy children (age 0-21years) and were retrospectively analyzed. The global longitudinal strain (GLS) was obtained by 2D speckle tracking using Philips Epiq7® and QLAB post processing software. The normative value for left ventricular GLS (%) obtained in our study was - 20.8 ± 2.3 (< 1year); - 21.4 ± 2.2 (1-4years); - 19.6 ± 2.4 (5-9years); - 19.4 ± 2.6 (10-14years); - 18.9 ± 3.0 (15-21years). There was a statistically significant difference in GLS between the different age groups. The BMI (kg/m2) of assessed subjects were 14.6 ± 2.3 (< 1year); 16.3 ± 1.5 (1-4years); 16.7 ± 2.3 (5-9years); 21.3 ± 4.6 (10-14years); 23.9 ± 5.9 (15-21years). There was no significant difference in GLS by gender or by BMI found in our study. We present our experience with establishment of normative values of 2DSTE in our pediatric echocardiography lab. This study shows that age is the major determinant of variation in peak GLS in healthy subjects, emphasizing the importance of establishment of normative data among various age groups in pediatrics.

Study on Strain Test Law of the Semi-rigid base Asphalt Pavement

In order to grasp the similarities and differences in the experimental strain law of different types of semi-rigid base asphalt pavement, based on the Yunluo highway durability test pavement, the strain monitoring system, temperature monitoring system and humidity monitoring system of the full-scale pavement were constructed, and corresponding test plans were formulated. Through the test scheme, the strain response laws of different structural layers of two asphalt pavements were obtained. Through the comparative analysis with the relevant theoretical analysis results, the rationality and credibility of the strain layout scheme and test scheme of the Yunluo durability test pavement were confirmed. Through the analysis of the measured strain data, it was verified that the graded crushed rock layer did have a decentralized effect on the load. At the same time, it was also confirmed that when the same pavement material was in different structural layers, its mechanical response under load was different.

STRESSING STATE CHARACTERISTICS OF REINFORCEMENT CONCRETE BOX-GIRDERS STRENGTHENED WITH CARBON FIBER REINFORCED PLASTIC

This paper investigates structural performance of five reinforcement concrete (RC) box-girders under a combination loading of bending, shear and torsion, applying the structural stressing state theory. The measured strain data is modeled as generalized strain energy density (GSED) to characterize the structural stressing state mode. Then the Mann-Kendall (M-K) criterion is innovatively applied to detect the leap characteristics of RC box-girders’ stressing state from the E’-T curves, deriving the new definition of structural failure load. Furthermore, the reinforcement effects of different Carbon Fiber Reinforced Plastic (CFRP) wrapping schemes on the behaviors of experimental RC box-girders are revealed through comparing strain modes of stirrup and longitudinal reinforcement. Finally, the method of numerical shape function is applied to reasonably expand the limited strain data for further exploring the strain distribution of cross section and analyzing the stressing state characteristics of the RC box-girders. The research results provide a new angle of view to conduct structural analysis and a reference to the improvement of reinforcement scheme.

Experimental and numerical investigation of debonding process of the FRP plate-concrete interface

Single shear tests performed to study the debonding between the concrete and the FRP plate of 2 mm thickness are presented. Specimens with five different bond lengths have been tested. In order to investigate the debonding mechanism and measure the complete strain distribution, digital image correlation (DIC) method was applied. The shear stress and slip distribution curves were calculated from the strain distribution functions fitted from measured strain data. Based on the features of the shear stress transfer zone under different load levels, the whole loading process has been divided into four stages: (1) elastic stage; (2) cracking stage; (3) debonding stage; (4) failure stage. According to the relationship between the relative bearing capacity and bond length, a concept of efficient bond length was suggested. A bi-linear bond stress-slip model was calibrated by the constitutive parameters of the experimental shear stress-slip curves. Based on the bi-linear bond stress-slip relationship, a numerical model of FRP plate-concrete interface was built using the bonded-particle model (BPM) and the debonding process was numerically analyzed. The numerical results present good agreement with the experimental results in the load-slip response and the shear stress distribution along the bond length. The comparison between the experimental and the numerical results shows that BPM can effectively simulate the debonding process of the FRP plate-concrete interface.

Deep Bayesian neural networks for damage quantification in miter gates of navigation locks

Inland navigation infrastructure like locks and dams form a vital part of the global economy. Locks facilitate the transport of hundreds of millions of dollars’ worth of goods on a daily basis. A primary cause for downtime of locks in the United States is damage to lock gates. Current inspection methods involve the complete closure of locks to visually inspect for damage. A common target of such inspections is the identification of “gaps” that form along the bearing surface boundary of miter gates. These gaps accelerate the fatigue failure of the gate by disrupting the designed load distribution mechanism. This article presents a novel engineering application of structural health monitoring for full-scale civil infrastructure with a method to automatically quantify the damage quantity of interest, that is, the gaps using measured strain data. We propose a framework for damage estimation of full-scale civil infrastructure in general and miter gates in particular, leveraging recent advances in deep Bayesian learning. A new two-term loss function is produced to increase the accuracy of the trained networks and the model uncertainties are conveyed using Monte Carlo dropout. In addition, we propose a strategy to model bearing surface gaps using non-linear contact analyses and use the proposed model to determine the sensitivity of measured strains to damage. The proposed framework is implemented for the miter gates at the Greenup locks and dam. Finally, the proposed methodology is validated using measured data. Slopes measured from the lock gate are used as the input to the trained networks to estimate the gap depths. The finite element model is updated using the estimated gap depths. The predicted slopes and strains from the updated model are shown to match the measured strains and slopes well. The results demonstrate the efficacy of the approach for damage detection in full-scale civil infrastructure.

Stressing State Analysis of CFST Arch Supports in Deep Roadway Based on NSF Method

This paper experimentally analyzes the working behavior characteristics of five concrete-filled steel tube (CFST) arch supports in deep roadway based on the numerical shape function (NSF) method and structural stressing state theory. First, the measured strain data are expanded by the NSF method and modeled as generalized strain energy density (GSED) to characterize the stressing state of the supports. Then, one of the supports is taken as an example and the Mann-Kendall (M-K) criterion is adopted to detect the mutation characteristics of the support, which derives the new definition of structural failure load. Correspondingly, the stressing state modes as well as strain and stress fields for the support are proposed to verify their mutation characteristics. Finally, the common and different characteristics of stressing state, damage development and internal forces for different supports are also summarized. The analytical results of the supports explore a new analysis method for underground structures and the unseen knowledge provides a reference to more rational future design.

Location identification of line supports using experimental modal analysis

In many engineering applications, line supports are used to reinforce long span structures such as multi-span beams and plates. However, the presence of line supports usually causes local stress concentration. Location identification of line supports is thus indispensable if these stress concentration areas are to be kept off. In this study, to address this issue an easy-to-implement approach was developed using experimental modal analysis (EMA) based on dynamic strain data. A novel index (gradient of strain modal shape vector) that can be calculated by the strain modal shapes of the investigated structure was proposed to assess the rate of change of strain vectors. Simulation results showed that the support locations and stress concentration areas can be easily identified using the plots of calculated index values. In the experimental verification, fiber Bragg grating (FBG) sensors were employed to measure the dynamic responses of a scaled multi-span rectangular plate structure subjected to hammer impact. The measured strain data along a path line on the top surface of the scaled model were used to construct strain modal shapes, further to plot corresponding curve of the proposed index, based on which the locations of line supports were identified successfully. The results showed that the proposed method was effective and convenient for practical applications.

International Research Status on Spent Nuclear Fuel Structural Integrity Tests Considering Vibration and Shock Loads Under Normal Conditions of Transport

Currently, the development of evaluation technology for vibration and shock load characteristics and spent nuclear fuel structural integrity under normal conditions of transport is being conducted in the Republic of Korea. This is the first such research conducted in the Republic of Korea and, thus, previous international studies need to be investigated and will be referred to in the ongoing project. Before 2000, several studies related to measurement of vibration and shock loads on spent nuclear fuel were conducted in the US. US national research institutes conducted uniaxial fuel assembly shaker tests, concrete block tests, and multi-axis fuel assembly tests between 2009 and 2016. In 2017, multi-modal transportation tests including road, sea, and rail transport were also performed by research institutes from the US, Spain and the Republic of Korea. Therefore, test preparation procedures, acceleration and strain measurement results, and finite-element and multi-body dynamics analysis were investigated. Based on the measured strain data, the preliminary conclusion was obtained that the measured strain was too small to cause damage to spent nuclear fuel rods. However, this conclusion is a preliminary conclusion that only reviews part of the results; a detailed review is being conducted in the US. The investigation of international studies on spent nuclear fuel structural integrity tests considering vibration and shock loads under normal conditions of transport in the US will be useful data for the project being conducted in the Republic of Korea.

Cure strain monitoring in composite laminates with distributed optical sensor

Measuring the strain history in pre-impregnated thermoset composites during the curing process provides valuable data for manufacturing specification development, quality control, diagnostics of dimensional stability, and validation of cure models. Distributed Optical Sensors (DOS) provide information along the entire optical path length of the sensor embedded in the laminate and present a promising high-resolution sensing option for in-situ strain measurement. This study’s contribution to the field is the coupling of the optical sensor monitoring of composite cure strain with models of the cure kinetics, viscosity, and glass transition temperature of the thermoset matrix. A unidirectional (UD) laminate and a structural laminate (SL) were manufacture embedded with an optical sensor. The internal residual strain developed during each stage of the thermal cure cycle is examined for both laminate types, including after cooling, and the models of the resin’s physical property development were used to facilitate interpretation of the strain measurement data from the DOS.

STRESSING STATE ANALYSIS OF LARGE CURVATURE CONTINUOUS PRESTRESSED CONCRETE BOX-GIRDER BRIDGE MODEL

This paper experimentally analyzes the working behavior characteristics of a large-curvature continuous prestressed concrete box-girder (CPCBG) bridge model based on structural stressing state theory. First, the measured strain data is modeled as generalized strain energy density (GSED) to characterize the stressing state of the bridge model. Then, the Mann-Kendall (M-K) criterion is adopted to detect the stressing state leaps of the bridge model according to the natural law from quantitative change to qualitative change of a system, which derives the new definition of structural failure load. Correspondingly, the stressing state modes for the bridge model’s sections and internal forces are proposed to verify their changing characteristics and the coordinate working behavior around the characteristic loads. The analytical results reveal the working behavior characteristics of the bridge mode unseen in traditional structural analysis, which provides a new angle of view to conduct structural analysis and a reference to the improvement of design codes.

Validation of Improved Sampling Concepts for Offshore Wind Turbine Fatigue Design

Fatigue damage is a design-driving phenomenon for substructures of offshore wind turbines. However, fatigue design based on numerical simulations is quite uncertain. One main reason for this uncertainty is scattering offshore conditions combined with a limited number of simulations (samples). According to current standards, environmental conditions are sampled using a deterministic grid of the most important environmental conditions (e.g., wind speed and direction, significant wave height, and wave period). Recently, there has been some effort to reduce the inherent uncertainty of damage calculations due to limited data by applying other sampling concepts. Still, the investigation of this uncertainty and of methods to reduce it is a subject of ongoing research. In this work, two improved sampling concepts—previously proposed by the authors and reducing the uncertainty due to limited sampling—are validated. The use of strain measurement data enables a realistic estimate of the inherent uncertainty due to limited samples, as numerical effects, etc., are excluded. Furthermore, an extensive data set of three years of data of two turbines of the Belgian wind farm Northwind is available. It is demonstrated that two previously developed sampling methods are generally valid. For a broad range of model types (i.e., input dimensions as well as degrees of non-linearity), they outperform standard sampling concepts such as deterministic grid sampling or Monte Carlo sampling. Hence, they can reduce the uncertainty while keeping the sampling effort constant, or vice versa.

Determination of Layer Modulus Master Curve for Steel Deck Pavement using Field-Measured Strain Data

Orthotropic steel deck (OSD) bridges have gained increasing popularity around the world during the past 20 years. The steel deck pavement is one of the major components of an OSD bridge and a well-designed pavement is essential to extend the service life of the bridge. To optimize the design method for OSD pavements, this study evaluated the strain responses and the layer moduli of a field OSD pavement under different loading conditions. Firstly, a series of field tests were conducted to measure the strain responses of the OSD pavement. The test results then were analyzed to evaluate the effects of loading speed and temperature on the strain values and response frequencies of the pavement. Secondly, a finite element model of the bridge-pavement system was established to back-calculate the layer moduli of the field OSD pavement from the measured strain data. Based on the back-calculation results, the master curves for the layer moduli of the pavement were determined and validated. These master curves can reflect the actual modulus properties of the field OSD pavement and be used to calculate strain-stress state in the OSD pavement at any temperature as well as loading speed. Thus the critical strain and stress within the pavement can be determined, which should provide the reference for the design of this type of pavement.

Local Stress-Field Reconstruction Around Holes in a Plate Using Strain Monitoring Data and Stress Function

This study reconstructs a two-dimensional stress field from measured strain data. The advantage of using stress functions is that the stress equilibrium and strain compatibility are automatically satisfied. We use the complex stress functions given by the finite series of polynomials. Then, we find the proper set of coefficients required to make the best fit to the measured strain data. Numerical examples represent the stress concentration problems around a hole(s) in a plate. It is demonstrated that the present method reconstructs the stress field around the hole(s), and the estimated stress agrees with the finite element (FE) analysis result.

Analysis of Strain Law of Structural Layer of Semi-rigid Base Asphalt Pavement with Graded Crushed Rock

Based on the long-life test road project of Yunluo expressway in Guangdong province, the strain law of the semi-rigid asphalt pavement with graded crushed rock was analyzed and studied. Firstly, the ANSYS finite element analysis model was established according to the structure of Yunluo long-life test road, and the strain data of corresponding points were extracted according to the strain arrangement scheme of Yunluo test road. Secondly, FWD was used as the loading device, and the strain data of different points of the corresponding structure layer were obtained according to the test scheme of the long-life test road of Yunluo. Finally, through the analysis of the theory and the measured strain data, the strain law of the semi-rigid base asphalt pavement with graded gravel rock was obtained. To grasp the mechanical response law of this type of asphalt pavement structure, it would provide useful help for the design, construction and maintenance of the semi-rigid base asphalt pavement structure with the graded crushed rock.