MEMS Stress Test Cell for Nanofiber Tensile Measurement
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Solution Overview
Problem
Current methods for testing the mechanical properties of polymeric nanofibers are limited by batch-to-batch variations, fragility, and lack of suitable tension testing techniques that conform to standard protocols, often resulting in qualitative and inaccurate results due to the small dimensions and high elasticity of these fibers.
Innovation Solution
A stress micro mechanical system using MEMS fabrication with freestanding sample attachment points and optical microscopy for digital image correlation to measure stress and strain, allowing for accurate tensile testing of micro- and nano-fibers with sub-pixel resolution and high strain rates, while avoiding the limitations of electron microscopy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If AFM cantilevers and SEM are used for tension testing of nanofibers, then force and displacement can be measured, but measurement precision deteriorates due to increasing relative error when cantilever stiffness differs substantially from nanofiber stiffness
Solution Approach 1:
The patent replaces the AFM cantilever-based mechanical measurement system with an optical measurement system using a microscope and video imaging. This substitution eliminates the stiffness-matching requirement and reduces measurement errors by using optical methods to track nanofiber deformation and calculate mechanical properties through image analysis software.
Solution Approach 2:
The patent introduces an optical microscope and video imaging system as an intermediary between the mechanical testing apparatus and the nanofiber sample. This intermediary system captures images of the nanofiber during tension testing, allowing precise measurement of deformation and force without direct mechanical contact that would introduce stiffness-related measurement errors.
2Device complexity
If all-MEMS test cells with on-chip actuators are used, then device complexity is reduced and fabrication cost decreases, but measurement precision deteriorates due to limited range of force and displacement
Solution Approach 1:
The patent segments the testing system into separate functional components: a simple MEMS test cell structure for mechanical support and actuation, and a separate optical measurement system for precise imaging and analysis. This segmentation allows each component to be optimized independently - the MEMS cell for structural simplicity and the optical system for measurement precision.
Solution Approach 2:
The patent introduces optical imaging as an intermediary measurement method that decouples the mechanical testing function from the measurement function. This allows the use of simple MEMS actuators while maintaining high measurement precision through optical methods that can accurately track displacement and calculate force over extended ranges.
3Ease of manufacture
If nanoindentation, bending tests, or resonance frequency measurements are used, then testing can be performed, but measurement precision deteriorates due to qualitative results and failure to conform to ASTM standards
Solution Approach 1:
The patent replaces indirect mechanical testing methods (nanoindentation, bending, resonance) with direct optical tension testing. This substitution enables quantitative measurement of mechanical properties including tensile strength, elastic modulus, and strain behavior, while conforming to ASTM standards through direct application of tensile loading and optical measurement of the resulting stress-strain response.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables precise measurement of mechanical and adhesion properties of nanofibers with high resolution and accuracy, capable of testing fibers with large stretch ratios and various loading rates, overcoming the limitations of existing techniques by providing smooth stress-strain curves and accounting for fiber deformation beyond the optical diffraction limit.
Implementation Method 1
An optical microscope images surfaces of the MEMS fabrication
Implementation Method 2
Software conducts digital image correlation on obtained images to determine the movement of the surfaces at a resolution much greater than the hardware resolution of the optical microscope
Data Source
AI summary
The invention provides a stress micro mechanical system for measuring stress and strain in micro- and nano-fibers tubes, and wires as well as for measuring the interface adhesion force and stress in nanofibers and nanotubes embedded in a polymer matrix. A preferred system of the invention has a substrate for supporting a MEMS fabrication. The MEMS fabrication includes freestanding sample attachment points that are movable in a translation direction relative to one another when the substrate is moved and a sample is attached between the sample attachment points. An optical microscope images surfaces of the MEMS fabrication. Software conducts digital image correlation on obtained images to determine the movement of the surfaces at a resolution much greater than the hardware resolution of the optical microscope. A preferred method for measuring stress and strain in micro- and nano-fibers, tubes, and wires, and/or measuring the force required to pull-out individual micro- and nano-fibers, tubes, and wires from a polymer matrix and to therefore measure interfacial adhesion is also provided. In the method a sample is attached between freestanding platforms in a MEMS device. Relative translational movement between the platforms is created and motion of the platforms is imaged with an optical microscope. Mechanical and adhesion properties of the sample are determined by applying a digital image correlation algorithm to the image data.