Optical strain measurements on fast moving fiber reinforced polymer rotors using diffraction gratings

2019 ◽  
Vol 86 (3) ◽  
pp. 175-183
Author(s):  
Julian Lich ◽  
Tino Wollmann ◽  
Angelos Filippatos ◽  
Maik Gude ◽  
Robert Kuschmierz ◽  
...  
Keyword(s):  
Rigid Body ◽  
Strain Measurement ◽  
Composite Structures ◽  
Dynamical Behavior ◽  
Image Correlation ◽  
Fiber Reinforced Polymers ◽  
Strain Gauges ◽  
Objective Lens ◽  
Fiber Reinforced ◽  
Body Movements

AbstractIn-situ measurements of the deformation and of the structural dynamical behavior of moving composite structures, such as rotors made of glass fiber reinforced polymers (GFRP), are necessary in order to validate newly developed simulation models. Local methods like strain gauges and fiber Bragg gratings lack spatial resolution, while contactless optical methods like image correlation or speckle interferometry suffer from noise effects in the presence of fast rigid body movements. A novel compact sensor – based on the diffraction grating method – is introduced for spatially and temporally resolved strain measurement. The use of a line camera allows the measurement of vibrations up to several tens of kHz. With a scanning movement, strain fields at submillimeter resolution can be recorded. The use of two diffraction orders and an objective lens reduces cross sensitivities to rigid body movements on the strain measurement by two to three orders of magnitude. A validation on a GFRP probe was conducted in a quasi-static tensile test with an optical extensometer up to 14500 µϵ. Furthermore, a strain measurement on a moving rotor at surface speeds up to 75 m/s was performed and the results were compared with those of strain gauges as a gold standard. The statistical standard deviation was around 10 µϵ and independent of the rotational speed.

scholarly journals Comparison of Resistive and Optical Strain Measurement for Early Fracture Detection

2020 ◽  
Vol 6 (3) ◽  
pp. 196-199
Author(s):  
Alina Carabello ◽  
Constanze Neupetsch ◽  
Michael Werner ◽  
Christian Rotsch ◽  
Welf-Guntram Drossel ◽  
...  
Keyword(s):  
Surgical Training ◽  
Error Detection ◽  
Strain Measurement ◽  
Testing Machine ◽  
Image Correlation ◽  
Strain Gauges ◽  
Measurement Technology ◽  
Bone Surface ◽  
Fracture Detection ◽  
Local Strains

AbstractTo increase learning success in surgical training, physical simulators are supplemented by measurement technology to generate and record objective feedback and error detection. An opportunity to detect fractures following hip stem implantation early can be measurement of occurring strains on bone surface. These strains can be determined while using strain gauges, digital image correlation (DIC) or photoelasticity. In this research strain gauges and DIC were compared regarding their suitability as strain measurement tools for use in physical simulators. Therefore a testing method was described to replicate the implantation of a hip stem. Testing devices modelled on a realistic prosthesis were pressed into prepared porcine femora in a two-step procedure with a material testing machine. The local strains occurring on bone surface were determined using an optical measurement system for DIC and strain gauges. The initial fractures in the tested femora are located medial-anterior in most cases (73,6%). With increasing indentation depth of the test device, the strains on bone surface increase. Comparing the local strains determined by DIC and strain gauges consistencies in curves are noticeable. Maximal determined strains before fracturing amount to 0,69% with strain gauges and 0,75% with DIC. In the range of the fracture gap, strain gradients are determined by using DIC. However the detected surfaces are of low quality caused by gaps and motion artefacts. The results show strains on bone surfaces for early fracture detection are measurable with strain gauges and DIC. DIC is assessed as less suitable compared to strain gauges. Furthermore strain gauges have greater level of integration and economic efficiency, so they are preferred the use in surgical training simulators.

Visual Image Correlation Compared to Discrete Instrumentation for Measurement of Compressive Strains for Strain Based Design

2017 ◽  
Author(s):  
Jason Bergman ◽  
Ming Liu ◽  
Chris Timms
Keyword(s):  
Finite Element ◽  
Direct Measurement ◽  
Strain Measurement ◽  
Measurement Techniques ◽  
Visual Image ◽  
Slope Instability ◽  
Image Correlation ◽  
Strain Gauges ◽  
Line Pipe ◽  
Strain Capacity

Strain-based design philosophies have been developed to ensure safe pipeline operation through regions of slope instability, seismic activity or discontinuous permafrost while extending the life expectancy of the pipeline in those zones. Strain-based design methodology typically involves a comparison of the strain demand (estimated conservatively using numerical pipe-soil interaction analysis techniques) to the strain capacity (predicted using experimentally benchmarked models). This paper presents a comparison of measurement techniques for laboratory testing of critical compressive strain capacity (CCS). The CCS is defined as the strain coinciding with the peak bending moment, averaged over a gauge length often selected as one pipe diameter across the buckle location. As explored in previous work [1], the three most common methods to measure strain on the specimen intrados, with respect to bending, include 1) direct measurement using strain gauges on the intrados with respect to bending, 2) calculation of CCS from the output of discrete instrumentation (DI) including strain gauges and inclinometers; and 3) direct measurement of surface strains using Visual Image Correlation (VIC) techniques. In 2015 and 2016, the Centre for Reliable Energy Systems (CRES) and C-FER Technologies 1999 Inc. (C-FER) collaborated on a series of full-scale experiments (performed by C-FER) and detailed finite element analysis (FEA) (performed by CRES) intended to assess and understand the effect of various anomalies on the strain capacity of line pipe. To facilitate comparison of the DI strain measurement method and the newer VIC method, these tests were conducted using both methods. The results demonstrate that the VIC technique can provide a more complete measure of the strain field and greater accuracy in cases where uneven strain distributions challenge the assumptions associated with DI methods. High level test data is presented and one test displaying the discrepancy between VIC and DI results is described. Finite element modelling, employed to explore the digression observed between the two strain measurement methods, is also presented and the comparative results of the two strain measurement techniques are discussed.

Optical Strain Measurement Techniques to Assist in Life Monitoring of Power Plant Components

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
Andrew Morris ◽  
Chris Maharaj ◽  
Miltiadis Kourmpetis ◽  
Ian Dear ◽  
Amit Puri ◽  
...  
Keyword(s):  
Power Plant ◽  
Creep Strain ◽  
Strain Measurement ◽  
Measurement Techniques ◽  
Image Correlation ◽  
Strain Gauges ◽  
Element Analysis ◽  
Operational Conditions ◽  
Optical Strain ◽  
Plant Components

Sensors for monitoring creep strain in high-pressure steam pipes and other power plant components are subjected to very demanding environmental and operational conditions. It is important that the sensors are of a rugged design and that measurement can be made that only relates to creep movements in power plant components. The E.ON UK auto-reference creep management and control (ARCMAC) optical strain gauges have been designed to have this capability. These optical strain gauges are installed across sections of welded steam pipe and other plant components in locations that provide the best monitoring points to reveal the early onset of failure processes. Reported in this paper are recent developments to improve optical creep strain measurement to achieve a 65 microstrain accuracy level with an error of less than 10%. Also reported are trials of combining optical strain gauges with digital image correlation (DIC) to obtain detailed information of the creep strain distribution around the gauges. The DIC data for known defect geometries have been validated with finite element analysis.

Use of Open Source DIC Tools for Analysis of Multiple Cracking in Fiber-Reinforced Concrete

2016 ◽  
Vol 827 ◽  
pp. 336-339 ◽  
Author(s):  
Václav Nežerka ◽  
Jakub Antoš ◽  
Tereza Sajdlová ◽  
Pavel Tesárek
Keyword(s):  
Open Source ◽  
High Performance ◽  
Fiber Reinforced Concrete ◽  
Image Correlation ◽  
Strain Gauges ◽  
Fiber Reinforced ◽  
Multiple Cracking ◽  
Strain Fields ◽  
Simple Rules

Digital image correlation (DIC) became indispensable when monitoring and analyzing adevelopment of displacement or strain fields. The method is capable of capturing strain localization, itis not limited to a relative measurement of discrete points as conventional methods and appears to bemore accurate than measurements by means of extensometers or strain-gauges that often suffer fromimperfect attachment to the measured surface. As open source DIC tools appear, the method becomesfeasible and the development is supported by the growing computational power of modern computers.The presented paper introduces open source 2D DIC tools and simple rules to follow when employingthe method. The presented case study on behavior of fiber reinforced high-performance concretedemonstrates a computational feasibility, accuracy and sensitivity of the method for a relatively lowfinancial cost.

scholarly journals Curved Foldable Tailored Fiber Reinforcements for Moldless Customized Bio-Composite Structures. Proof of Concept: Biomimetic NFRP Stools

Polymers ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 2000 ◽  
Author(s):  
Gabriel Rihaczek ◽  
Maximilian Klammer ◽  
Okan Başnak ◽  
Jan Petrš ◽  
Benjamin Grisin ◽  
...  
Keyword(s):  
Composite Structures ◽  
Role Model ◽  
Building Materials ◽  
Natural Fiber ◽  
Weight Ratio ◽  
Design Tool ◽  
Fiber Reinforced Polymers ◽  
Fiber Reinforced ◽  
Resource Saving ◽  
Fiber Placement

Fiber Reinforced Polymers (FRPs) are increasingly popular building materials, mainly because of their high strength to weight ratio. Despite these beneficial properties, these composites are often fabricated in standardized mass production. This research aims to eliminate costly molds in order to simplify the fabrication and allow for a higher degree of customization. Complex three-dimensional shapes were instead achieved by a flat reinforcement, which was resin infused and curved folded into a spatial object before hardening. Structural stability was gained through geometries with closed cross-sections. To enable this, the resource-saving additive fabrication technique of tailored fiber placement (TFP) was chosen. This method allowed for precise fibers’ deposition, making a programmed anisotropic behavior of the material possible. Principles regarding the fiber placement were transferred from a biological role-model. Five functional stools were produced as demonstrators to prove the functionality and advantages of the explained system. Partially bio-based materials were applied to fabricate the stool models of natural fiber-reinforced polymer composites (NFRP). A parametric design tool for the global design and fiber layout generation was developed. As a result, varieties of customized components can be produced without increasing the design and manufacturing effort.

scholarly journals Reinforcing effect of a thin basalt fiber-reinforced polymer plywood coating

BioResources ◽  
2019 ◽  
Vol 14 (1) ◽  
pp. 2062-2078
Keyword(s):  
Bending Strength ◽  
Basalt Fiber ◽  
Image Correlation ◽  
Fiber Reinforced Polymers ◽  
Strengthening Effect ◽  
Fiber Reinforced ◽  
Reinforced Polymers ◽  
Reinforcing Effect ◽  
Highest Weight ◽  
The Impact

The strengthening effect of basalt fiber-reinforced epoxy coatings was investigated with regard to their areal weight and position on the compression or tension side of plywood. Beach plywood was coated on one side with a basalt fiber-reinforced epoxy matrix. Two biaxial and one twilled fabric with areal weights of 170 g/m2, 210 g/m2, and 340 g/m2 respectively were used. The thickness of the plywood was 21 mm. The results showed the best reinforcing effect was obtained with the highest weight when mounted on the tension side of the parallel specimens. The bending strength of these specimens was improved by 15.7%. The perpendicular specimens were positively reinforced by the fiber-reinforced polymers on both the compression and tension sides. The tension reinforcement provided a higher deflection, which was further analyzed using digital image correlation. The evaluated data indicated significant displacement of the neutral axis. The impact strength of the parallel specimens was not improved by the reinforcement, but all of the reinforced perpendicular specimens were significantly strengthened.

scholarly journals Experimental Identification of Statistical Correlation between Mechanical Properties of FRP Composite

Materials ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 674 ◽  
Author(s):  
Shufeng Zhang ◽  
Tongzhen Xing ◽  
Haibin Zhu ◽  
Xun Chen
Keyword(s):  
Mechanical Properties ◽  
Composite Structures ◽  
Accurate Determination ◽  
Correlation Coefficients ◽  
Field Method ◽  
Statistical Correlation ◽  
Image Correlation ◽  
Experimental Methodology ◽  
Fiber Reinforced ◽  
Frp Composite

Recent prediction on the heavy statistical correlation between the mechanical properties of fiber reinforced composite (FRP) raises new concerns on the accurate reliability evaluation of composite structures, but such statistical correlation still lacks experimental verification. In this work, an experimental methodology is proposed to determine the statistical correlation between mechanical properties of unidirectional FRP composite. A rectangular shaped carbon fiber reinforced plastic (CFRP) specimen with a circular hole is loaded by tension, and 3D digital image correlation (DIC) is employed to characterize the heterogeneous strain field around the hole. Virtual field method (VFM) is used to derive E11, E22, ν12, and G12 of specimens. Specimen configuration considering fiber angle and hole diameter is optimized to achieve accurate determination of correlation coefficients. Experimental results on the linear correlation coefficients between E11, E22, ν12, and G12 agree well with previous theoretical predictions.

Experimental Specimen for Classification of Matrix Compression Damage in Carbon Fiber Reinforced Polymers

2018 ◽  
Author(s):  
Taylor J. Rawlings ◽  
Kevin T. Carpenter ◽  
John P. Parmigiani
Keyword(s):  
Carbon Fiber ◽  
Crack Propagation ◽  
Visible Region ◽  
Material Model ◽  
Image Correlation ◽  
Fiber Reinforced Polymers ◽  
Fiber Reinforced ◽  
Matrix Compression ◽  
Carbon Fiber Reinforced ◽  
Compression Damage

Composite materials are becoming increasingly common in the aerospace industry. In order for simulation and modeling to accurately predict failure of composites, a material model based on observed damage mechanisms is required. Composites are commonly classified into four damage categories based on the composite constituents and their loading condition: fiber tension, fiber compression, matrix tension, and matrix compression. Previous work identified a compact compression (CC) specimen as a suitable option for isolating matrix compression damage. However upon continued testing, stable crack propagation in the specimen was limited to a relatively low material failure ratio (σCompressive/σTension). This paper presents specimen geometry that can isolate matrix compression damage in materials with a failure ratio greater than two, the limit of the compact compression specimens. Initial specimen selection used the compact compression specimens from previous research and added additional specimens based on commonly used compressions specimens for different materials. The added specimens included center notched compression (CNC), edge notch compression (ENC), and four-point bending (4PB). All specimens were evaluated experimentally with the success criteria of controlled propagation of a matrix compression crack. In addition to propagating a controlled matrix compression crack, specimens were required to have a visible region around the stress concentrator to allow for digital image correlation (DIC) image capture during the experiments. The specimens were manufactured from a carbon fiber reinforced polymer (CFRP) with a failure ratio greater than six. CC and 4PB specimens were unable to produce a compression crack before any other failure methods were present. CNC specimens produced an unstable compression crack that progressed from the notch to the edge of the specimen too rapidly to acquire meaningful crack propagation data. ENC specimens showed some ability to stably propagate a crack, however some tests resulted in an unstable crack propagation similar to the CNC specimens. In order to increase the test repeatability, a tapered thickness was added to the specimen around the notch tip. The resulting tapered ENC (TENC) produced repeatable controlled matrix compression crack propagation. Ultimately, the specimen fails when the crack has propagated through the entire width of the specimen. TENC specimens show promise for isolating matrix compression damage in materials with high failure ratios. Continued testing of CFRP with TENC specimens could be used to refine the material model for finite element analysis.

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