Bond–Slip Law Between Steel Bar and Different Cement-Based Materials Considering Anchorage Position Function

The bond performance between steel bar and cement-based materials was the prerequisite for the two materials to work together, and previous studies showed that the bond behavior of the steel bars and cement-based materials will vary with the kinds of cement-based materials. For this reason, this paper adopted 12 direct pullout test specimens including three types of concrete and two types of steel bars. The strain of the steel bar at six measuring points was measured with a strain gauge. Based on the measured strain and free end slip of the steel bars, the distribution of steel stress, bond stress, and relative slip and the bond slip relation along the anchorage length were obtained and analyzed for different concrete and different steel bars. Based on these test results of steel strain and relative slip at six measuring points, the anchorage position function could be established in consideration of anchorage position, which was conducive to the establishment of an accurate bond–slip relationship. In addition, the anchorage length of the steel bar in Engineered Cementitious Composites (ECC) calculated from the equilibrium equation of critical limit state is only half of the anchorage length calculated in the current Code for Design of Concrete Structures (GB 50010-2010) in China. It is suggested to establish the critical anchorage length formula suitable for ECC in future studies.

Feasability of Diaphragmatic Speckle Tracking In Intensive Care Units

Background: Diaphragmatic dysfunction is a common condition in intensive care units (ICU). Its presence correlates with prolonged weaning from mechanical ventilation and mortality. Diaphragmatic excursion (EXdi) and thickening fraction (TFdi) are the 2 main measures currently described in diaphragmatic ultrasound, but each has its limitations. Strain and strain rate are already used cardiac sonography and could be of interest in the assessment of diaphragmatic function in ICU. The aim of this work was to evaluate the feasibility of diaphragmatic strain and strain rate in ICU and to describe their distribution, reproducibility and agreement with existing parameters. Methods: All patients who underwent a T-tube weaning test were prospectively included. Ultrasound loops were recorded on each side of the patient during the last 30 minutes of the weaning test. Two operators measured strain, strain rate, EXdi, and TFdi blind to each other in post-treatment analysis. Results: Thirty patients were analyzed. The median values for strain and strain rate were -6.74% and -0.23.s-1 on the left side and -8.17% and -0.22.s-1 on the right side. Concerning strain and strain rate, intra-class coefficients showed systematically a very good reliability between operators. Conclusion: Diaphragmatic strain and strain rate measurements appeared feasible in an ICU environment and seemed reproducible and not strongly correlated with EXdi and TFdi. An improvement of the analysis software is needed to improve the ease of interpretation. The interest of these parameters in clinical practice should be explored in forthcoming studies.

GROWTH MONITORING OF DELAMINATION AND ADHESIVE DEBONDING OF CFRP STRUCTURES BY RAYLEIGH SCATTING-BASED DISTRIBUTION SENSORS

Since delamination of CFRP laminates is generated by impact or fatigue in aircraft operation, identification method of the delamination is a very important technology to ensure safety of aircraft. Recently, built-in sensors are paid attention as a real-time monitoring method of initiation and growth of delamination. Optical fiber sensors are promised as built-in sensors of FRP due to their high strength, durability and embeddability. In this paper, we applied a Rayleigh scattering-based distribution sensor to detect delamination and debonding of CFRP structures. This optical fiber sensor can measure strain distribution along a fiber with wide area range, high spatial and strain resolutions. The optical fiber sensors attached on the surface of laminates were used to detect delamination and adhesive debonding of DCB, ENF and SLJ (single lap joint) specimens. Pre-crack were formed by inserting a Teflon films between the layers or the laminate and adhesive layer during manufacturing. The experimental results of DCB tests showed that the position of delamination edge could be identified precisely from the measured sharp peak of strain distribution. From the results of ENF tests, it appeared that the strain distribution showed the maximum at the delamination edge and the detected delamination edge positions agreed very well with the observed positions. The measured strain distributions were almost same as simulated results by FEM. From the tensile test results of SLJ specimen, it appeared that strain distribution showed extremum at debonding edge. It was also shown that the measured strain distribution agreed well with simulated results by FEM. From the above results, it appeared that the open delamination and debonding could be easily identified from surface strain distribution measured by the Rayleigh scattering-based sensor.

Hydraulic-Fracture-Width Inversion Using Low-Frequency Distributed-Acoustic-Sensing Strain Data Part II: Extension for Multifracture and Field Application

Summary Low-frequency distributed-acoustic-sensing (LF-DAS) strain data are direct measurements of in-situ rock deformation during hydraulic-fracturing treatments. In addition to monitoring fracture propagation and identifying fracture hits, quantitative strain measurements of LF-DAS provide opportunities to quantify fracture geometries. Recently, we proposed a Green’s function–based algorithm for the inversion of LF-DAS strain data (Liu et al. 2020b) that shows an accurate estimation of fracture width near the monitor well with single-cluster completions. However, multicluster completions with tighter cluster spacings are more commonly adopted in recent completion designs. One main challenge in the inversion of LF-DAS strain data under such circumstances is that strain measurements at fracture-hit locations by LF-DAS are not reliable, which makes the individual contribution of each fracture to the measured strain data indistinguishable. In this study, we first extended the inversion algorithm to handle multiple fractures, investigated the uncertainties of the inversion results, and proposed possible mitigation to the challenges raised by completion designs and field data acquisition through a synthetic case study. Ideally, there are available data on both sides of each fracture so that the inverted width of each fracture can be obtained with a negligible error. In reality, the strain data are usually limited, providing less constraint on the width of individual fracture. Nevertheless, the inversion results provide an accurate estimation of the width summation of all fractures. To evaluate the individual fracture width, a time-dependent constraint is added to the inversion algorithm. We assume that the width at the current timestep is dependent on the width at the previous step and the width variation between the two timesteps. The width variation can be roughly estimated from LF-DASstrain-rate data at the fracture-hit location. This extra constraint helps to improve the inversion performance. Finally, a field example is presented. We show the width summation of all fractures and the width of each individual fracture as a function of treatment time. The time-dependent width profiles show consistent trends with the LF-DASstrain-rate data. The calculated strains from the inverted model match well with the LF-DAS measured strain data. The findings demonstrate the potential of LF-DAS data for quantitative hydraulic-fracture characterization and provide insights on better use of LF-DAS data. The direct information on fracture width helps to calibrate fracturing models and optimize the completion designs.

Monitoring of the Operational Conditions in Steel Pipes Using Fiber Optic Sensors

Oil and water transport pipeline systems are susceptible to damage due to harsh environmental conditions and operational factors, hence ongoing maintenance and inspection are required. The development of a continuous and reliable monitoring technique will ensure the safety usage of these structures and assist in the extension of their life span. In this study, the monitoring and assessment of pipelines are performed using a network of Fiber Bragg Grating (FBG) sensors mounted along the longitudinal and circumferential directions. The sensitivity of the measurements to assess pressure and flow variation in the pipe, in addition to leakage detection and localization were evaluated. Water at a controlled pressure and flowrate was pumped into the designed six-meter pipe testbed designed for this purpose. Leakage was simulated by opening one of the four designated valves installed on the pipe. The variation in the pressure inside the pipe highly impacted the amplitude of the measured strain increasing it significantly reaching 20%. An increase in flowrate had an inverse effect, it resulted in a 5% decrease in the amplitude of the measured strain drop. The change of hole leakage size greatly influenced the measured signal, resulting in a 55% change in amplitude between a 2 cm2 and a 5 cm2 hole leakage. For the location of leakage, only the temporal aspects of the signal were affected resulting in a slight shift in the response time of sensors relative to each other. The results were promising to monitor the structural conditions related to leakage detection and localization, based on the patterns observed.

Estimation of Correct Long-Seam Mismatch Using FEA to Compare the Measured Strain in a Non-Destructive Testing of a Pressurant Tank

This paper discusses the design criterion of a pressurant steel tank made of HSLA 15CDV6 and proof pressure test (PPT) as a non-destructive examination. An inverse Ramberg-Osgood relation is used to represent the stress-strain curve of the material. Elasto-plastic finite element analysis (FEA) has been carried out to examine the adequacy of the design. Experimental stress analysis has been carried out from the measured strains and found maximum effective stress is at LS joint (max. measured strain location). Strain obtained from FEA is compared reasonably well with the proof pressure test (PPT) data at most of the strain gauge locations except at one long-seam (LS) joint. So, to explain the causes of difference in strains near one LS, parametric studies have been performed in a 3D FEA with varying LS mismatch to find the correct mismatch as a reverse engineering problem. It is found that a mismatch value of 0.9 mm will give the required strain at PPT, which is measured only 0.4 mm. The failure pressure estimated through nonlinear FEA/analytical expressions found to meet the design.

Verification of the Propagation Range of Respiratory Strain Using Signal Waveform Measured by FBG Sensors

The FBG (Fiber Bragg grating) sensor is an optical fiber type strain sensor. When a person breathes, strain occurs in the lungs and diaphragm. This was verified using an FBG sensor to which part of the living body this respiratory strain propagates. When measured in the abdomen, the signal waveforms were significantly different between breathing and apnea. The respiratory cycle measured by the temperature sensor attached to the mask and the strain cycle measured by the FBG sensor almost matched. Respiratory strain was measured in the abdomen, chest, and shoulder, and the signal amplitude decreased with distance from the abdomen. In addition, the respiratory rate could be calculated from the measured strain signal. On the other hand, respiratory strain did not propagate to the elbows and wrists, which were off the trunk, and the respiratory time, based on the signal period, could not be calculated at these parts. Therefore, it was shown that respiratory strain propagated in the trunk from the abdomen to the shoulder, but not in the peripheral parts of the elbow and wrist.

Camera-based optical palpation

Optical elastography is undergoing extensive development as an imaging tool to map mechanical contrast in tissue. Here, we present a new platform for optical elastography by generating sub-millimetre-scale mechanical contrast from a simple digital camera. This cost-effective, compact and easy-to-implement approach opens the possibility to greatly expand applications of optical elastography both within and beyond the field of medical imaging. Camera-based optical palpation (CBOP) utilises a digital camera to acquire photographs that quantify the light intensity transmitted through a silicone layer comprising a dense distribution of micro-pores (diameter, 30–100 µm). As the transmission of light through the micro-pores increases with compression, we deduce strain in the layer directly from intensity in the digital photograph. By pre-characterising the relationship between stress and strain of the layer, the measured strain map can be converted to an optical palpogram, a map of stress that visualises mechanical contrast in the sample. We demonstrate a spatial resolution as high as 290 µm in CBOP, comparable to that achieved using an optical coherence tomography-based implementation of optical palpation. In this paper, we describe the fabrication of the micro-porous layer and present experimental results from structured phantoms containing stiff inclusions as small as 0.5 × 0.5 × 1 mm. In each case, we demonstrate high contrast between the inclusion and the base material and validate both the contrast and spatial resolution achieved using finite element modelling. By performing CBOP on freshly excised human breast tissue, we demonstrate the capability to delineate tumour from surrounding benign tissue.