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This work presents a strain measurement sensor consisting of an amplification mechanism and a polydimethylsiloxane microscope manufactured using an improved 3D printer.
A traditional strain measurement sensor needs to be electrified and is susceptible to electromagnetic interference. In order to solve the fluctuations in the analog electrical signal in a traditional strain gauge operation, a new strain measurement method is presented here. It uses a photographic technique to display the strain change by amplifying the change of the pointer displacement of the mechanism. A visual polydimethylsiloxane (PDMS) lens with a focal length of 7.16 mm was added to a smartphone camera to generate a lens group acting as a microscope to capture images. It had an equivalent focal length of 5.74 mm. Acrylonitrile butadiene styrene (ABS) and nylon amplifiers were used to test the influence of different materials on the sensor performance. The production of the amplifiers and PDMS lens is based on improved 3D printing technology. The data obtained were compared with the results from finite element analysis (FEA) to verify their validity. The sensitivity of the ABS amplifier was 36.03 ± 1.34 µε/µm, and the sensitivity of the nylon amplifier was 36.55 ± 0.53 µε/µm.
Obtaining light but strong materials is particularly important in modern industry. The properties of materials are affected when subjected to stress, pressure, torsion, and bending vibration during use1,2. Thus, strain measurement of materials is important to analyze their durability and troubleshoot usage. Such measurements enable engineers to analyze the durability of materials and troubleshoot production problems. The most common strain measurement method in industry uses strain sensors3. Traditional foil sensors are widely used because of their low cost and good reliability4. They measure the changes in electrical signals and convert them to different output signals5,6. However, this method leaves out the details of the strain profile in the measured object and is susceptible to noise from vibrational electromagnetic interference with analog signals. Developing accurate, highly repeatable, and easy material strain measurement methods is important in engineering. Thus, other methods are being studied.
In recent years, nanomaterials have drawn much interest from investigators. To measure strain on small objects, Osborn et al.7,8 proposed a method to measure the strain of 3D nanomaterials using electron backscatter (EBSD). Using molecular dynamics, Lina et al.9 investigated the interlayer friction strain engineering of graphene. Distributed optical fiber strain measurements using Rayleigh backscatter spectroscopy (RBS) have been widely used in fault detection and for the evaluation of optical devices due to their high spatial resolution and sensitivity10. Grating fiber optic (FBG)11,12 distributed strain sensors have been widely used for high-precision strain measurement13 for their sensitivity to temperature and strain. In order to monitor the strain changes caused by curing after resin injection, Sanchez et al.14 embedded a fiberoptic sensor into an epoxy carbon fiber plate and measured the complete strain process. Differential interference contrast (DIC) is a powerful measurement method of the field deformation15,16,17 that is widely used as well18. By comparing the changes of measured surface gray levels in the collected images, the deformation is analyzed, and the strain calculated. Zhang et al.19 proposed a method that relies on the introduction of reinforced particles and DIC images to evolve from traditional DIC. Vogel and Lee20 calculated strain values using an automatic two-view method. In recent years, this enabled simultaneous microstructure observation and strain measurement in particle-reinforced composites. Traditional strain sensors only effectively measure strain in one direction. Zymelka et al.21 proposed an omnidirectional flexible strain sensor that improves a traditional strain gauge method by detecting changes in the sensor resistance. It is also possible to measure strain using biological or chemical substances. For instance, ionic conductive hydrogels are an effective alternative to strain/tactile sensors due to their good tensile properties and high sensitivity22,23. Graphene and its composites have excellent mechanical properties and provide a high carrier mobility along with good piezoresistivity24,25,26. Consequently, graphene-based strain sensors have been widely used in electronic skin health monitoring, wearable electronics, and other fields27,28.
In this work, a conceptual strain measurement using a polydimethylsiloxane (PDMS) microscope and an amplification system is presented. The device is different from a traditional strain gauge because it does not require wires or electrical connections. Moreover, displacement can be observed directly. The amplification mechanism can be placed at any location on the tested object, which greatly increases the repeatability of the measurements. In this study, a sensor and a strain amplifier were made by 3D printing technology. We first improved the 3D printer to increase its efficiency for our requirements. A spherical extrusion device was designed to replace the traditional single-material extruder controlled by the slicing software to complete the conversion of the metal and plastic nozzles. The corresponding molding platform was changed, and the displacement-sensing device (amplifier) and the reading device (PDMS microscope) were integrated.
1. Assembly of the amplification mechanism
2. Assembly of the PDMS microscope
3. Strain measurement for loading tests in the control and test groups
4. Finite element analysis
When the platform temperature increased, the droplet diameter and the curvature radius decreased, whereas the contact angle increased (Figure 3). Therefore, the focal length of the PDMS increased. However, for platform temperatures above 220 °C, a very short curing time was observed in the droplets, and they could not extend into a plane-convex shape. This can be attributed to the low attachment area when adhering onto a smartphone camera. Therefore, only soft lenses formed at 220 °...
The output displacement evolved linearly with the force concentrated at the free end of the cantilever beam and was consistent with the FEA simulations. The sensitivity of the amplifiers was 36.55 ± 0.53 με/μm for nylon and 36.03 ± 1.34 με/μm for ABS. The stable sensitivity confirmed the feasibility and the effectiveness of the rapid prototyping of high-precision sensors using 3D printing. The amplifiers had a high sensitivity and were free of electromagnetic interference. In addit...
The authors declare no conflicting interests.
This work was financially supported by the National Science Foundation of China (Grant No. 51805009).
Name | Company | Catalog Number | Comments |
ABS | Hengli dejian plastic electrical products factory | Used for printing 1.75 mm diameter wire for amplifying mechanism | |
Aluminum 6063 T83 bar | The length, width and thickness of cantilever beam are 380 mm, 51 mm, and 3.8 mm. | ||
ANSYS | ANSYS | ANSYS 14.5 | |
CURA | Ultimaker | Cura 3.0 | Slicing softare,using with the improved 3D printer |
Curing agent | Dow Corning | PDMS and curing agent are mixed with the weight ratio of 10:1 | |
Driving device | Xinmingtian | E00 | |
Improved 3D printer and accessories | Made by myself. The rotary spherical lifting platform is adopted. The spherical lifting platform is equipped with a nozzle and a pipette, which can be switched and printed freely. With a rotary printing platform, the platform temperature can be freely controlled. | ||
iPhone 6 | Apple | MG4A2CH/A | 8-megapixel sensor and the equivalent focus distance is 29mm |
Magenetic stirrer | SCILOGEX | MS-H280-Pro | |
Nylon | Hengli dejian plastic electrical products factory | Used for printing 1.75 mm diameter wire for amplifying mechanism | |
PDMS | Dow Corning | SYLGARDDC184 | After the viscous mixture is heated and hardened, it can be combined with the lens amplification device of the mobile phone for image acquisition. |
Shape analyzer | Gltech | SURFIEW 4000 | |
Solidworks | Dassault Systems | Solidworks 2017 | Assist to modelling |
VISHAY strain gauge | Vishay | Used to measure the strain produced in the experiment. | |
VISHAY strain gauge indicator | Vishay | Strain data acquisition. |
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