scholarly journals From force-responsive molecules to quantifying and mapping stresses in soft materials

2020 ◽  
Vol 6 (20) ◽  
pp. eaaz5093 ◽  
Author(s):  
Yinjun Chen ◽  
C. Joshua Yeh ◽  
Yuan Qi ◽  
Rong Long ◽  
Costantino Creton
Keyword(s):  
Direct Method ◽  
Soft Materials ◽  
Internal Force ◽  
Optical Observations ◽  
Innovative Tool ◽  
Loaded Crack ◽  
Cross Linker ◽  
Multiple Network ◽  
Spatially Varying ◽  
Random Nature

Directly quantifying a spatially varying stress in soft materials is currently a great challenge. We propose a method to do that by detecting a change in visible light absorption. We incorporate a spiropyran (SP) force–activated mechanophore cross-linker in multiple-network elastomers. The random nature of the network structure of the polymer causes a progressive activation of the SP force probe with load, detectable by the change in color of the material. We first calibrate precisely the chromatic change in uniaxial tension. We then demonstrate that the nominal stress around a loaded crack can be detected for each pixel and that the measured values match quantitatively finite element simulations. This direct method to quantify stresses in soft materials with an internal force probe is an innovative tool that holds great potential to compare quantitatively stresses in different materials with simple optical observations.

scholarly journals Mechanochemistry unveils stress transfer during sacrificial bond fracture of tough multiple network elastomers

2021 ◽  
Author(s):  
Yinjun Chen ◽  
Gabriel Sanoja ◽  
Costantino Creton
Keyword(s):  
Molecular Level ◽  
Stress Transfer ◽  
Soft Materials ◽  
Multiple Network

The molecular level transfer of stress from a stiff percolating filler to a stretchable matrix is a crucial and generic mechanism of toughening in soft materials.

scholarly journals Influence of Strong Spatially Varying Near Fault Ground Motion on Steel Box Arch Bridge

2021 ◽  
Author(s):  
Zhen Liu ◽  
Shibo Zhang
Keyword(s):  
Ground Motion ◽  
Internal Force ◽  
Shaking Table ◽  
Element Analysis ◽  
Arch Bridge ◽  
Near Fault ◽  
Long Span ◽  
Spatial Propagation ◽  
Near Fault Ground Motion ◽  
Spatially Varying

Abstract In violent earthquakes, ground motion is considered to change dramatically in the process of spatial propagation. Strong spatially varying exists in ground motion near fault area, and it can cause the large-span and large stiffness structure to be damaged. In this paper, a typical long-span steel box arch bridge is selected as an engineering case. In order to simulate the spatially varying of near fault ground motion accurately, the records that sampled in former earthquake are used as ground motion input. The shaking table experiment and finite element analysis are used as analysis means. Through the analysis of the internal force and displacement response of the key position of the arch rib, it is found that the spatially varying in the near fault ground motion can bring severe seismic response .If the spatially varying is ignored, the damage of the bridge will be seriously underestimated.

scholarly journals INTERNAL FORCE FACTORS IN A SHEET BLANK MATERIAL WHEN DRAWING BY THE DIRECT METHOD.

2019 ◽  
Vol 77 (09) ◽  
pp. 241-251
Author(s):  
Denis Chemezov ◽  
◽  
Alexandr Korobkov ◽  
Ilya Filippov ◽  
Evgeniy Varavin ◽  
...  
Keyword(s):  
Direct Method ◽  
Internal Force ◽  
Sheet Blank

Performance Characterization of a PDMS-Based Microfluidic Device for Detecting Continuous Distributed Loads

2013 ◽  
Author(s):  
Peng Cheng ◽  
Wenting Gu ◽  
Jiayue Shen ◽  
Arindam Ghosh ◽  
Ali Beskok ◽  
...  
Keyword(s):  
Microfluidic Device ◽  
Microfluidic Devices ◽  
Soft Materials ◽  
Mechanical Analysis ◽  
Dynamic Loads ◽  
Experimental Setup ◽  
Static And Dynamic Loads ◽  
Spatially Varying ◽  
First Time

In this paper, the performance of a PDMS-based microfluidic device is thoroughly characterized for detecting continuous static and dynamic loads. This device comprises of a single PDMS rectangular microstructure and a set of electrolyte-enabled distributed transducers. It is fabricated by a standard fabrication process well developed for PDMS-based microfluidic devices. One potential application of this device is to measure spatially-varying mechanical properties of heterogeneous soft materials, through quasi-static, stress relaxation and dynamic mechanical analysis (DMA) tests. Thus, the response of this device to three types of inputs: static, step and sinusoidal, is examined with a custom experimental setup. For the first time, the capability of using a polymer-based microfluidic device to detect sinusoidal inputs is reported. The characterized results demonstrate the potential of using this device to measure soft materials.

Concurrent Spatial Mapping of the Elasticity of Heterogeneous Soft Materials via a Polymer-Based Microfluidic Device: A Preliminary Study

2013 ◽  
Author(s):  
Wenting Gu ◽  
Peng Cheng ◽  
Zhili Hao
Keyword(s):  
Data Analysis ◽  
Microfluidic Device ◽  
Soft Materials ◽  
Spatial Mapping ◽  
Related Data ◽  
Preliminary Study ◽  
Spatially Varying

This paper presents a preliminary study on achieving concurrent spatial mapping of the spatially-varying elasticity of heterogeneous soft materials via a polymer-based microfluidic device. Comprised of a single compliant polymer rectangular microstructure and a set of electrolyte-enabled distributed resistive transducers, this device is capable of detecting continuous distributed loads. Through pressing a specimen against the device by a rigid probe with precisely-controlled displacements, the spatially-varying elasticity of a specimen is captured by continuous distributed loads acting on the device and is further registered as discrete resistance changes at the locations of the transducers in the device. Concurrent spatial mapping is conducted on homogeneous and heterogeneous specimens, and the related data analysis is performed on the measured results to extract their elasticity. The obtained results demonstrate the feasibility of concurrent spatial mapping of the spatially-varying elasticity of heterogeneous soft materials via this polymer-based microfluidic device.

scholarly journals Time-dependent mechanical characterization of poly(2-hydroxyethyl methacrylate) hydrogels using nanoindentation and unconfined compression

2008 ◽  
Vol 23 (5) ◽  
pp. 1472-1481 ◽  
Author(s):  
Jessica D. Kaufman ◽  
Gregory J. Miller ◽  
Elise F. Morgan ◽  
Catherine M. Klapperich
Keyword(s):  
Stress Relaxation ◽  
Material Properties ◽  
Viscoelastic Model ◽  
Soft Materials ◽  
Elastic Model ◽  
Equilibration Time ◽  
Hydroxyethyl Methacrylate ◽  
Unconfined Compression ◽  
Cross Linker ◽  
Relaxation Curves

Hydrogels pose unique challenges to nanoindentation including sample preparation, control of experimental parameters, and limitations imposed by mechanical testing instruments and data analysis originally intended for harder materials. The artifacts that occur during nanoindentation of hydrated samples have been described, but the material properties obtained from hydrated nanoindentation have not yet been related to the material properties obtained from macroscale testing. To evaluate the best method for correlating results from microscale and macroscale tests of soft materials, nanoindentation and unconfined compression stress-relaxation tests were performed on poly-2-hydroxyethyl methacrylate (pHEMA) hydrogels with a range of cross-linker concentrations. The nanoindentation data were analyzed with the Oliver–Pharr elastic model and the Maxwell–Wiechert (j = 2) viscoelastic model. The unconfined compression data were analyzed with the Maxwell–Wiechert model. This viscoelastic model provided an excellent fit for the stress-relaxation curves from both tests. The time constants from nanoindentation and unconfined compression were significantly different, and we propose that these differences are due to differences in equilibration time between the microscale and macroscale experiments and in sample geometry. The Maxwell–Wiechert equilibrium modulus provided the best agreement between nanoindentation and unconfined compression. Also, both nanoindentation analyses showed an increase in modulus with each increasing cross-linker concentration, validating that nanoindentation can discriminate between similar, low-modulus, hydrated samples.

scholarly journals Light-Actuated Liquid Crystal Elastomer Prepared by Projection Display

Materials ◽  
2021 ◽  
Vol 14 (23) ◽  
pp. 7245
Author(s):  
Juan Chen ◽  
Oluwafemi Isaac Akomolafe ◽  
Jinghua Jiang ◽  
Chenhui Peng
Keyword(s):  
Liquid Crystal ◽  
Three Dimensional ◽  
Topological Defects ◽  
Soft Materials ◽  
Liquid Crystal Elastomer ◽  
Projection Display ◽  
Liquid Crystal Elastomers ◽  
Spatially Varying ◽  
External Stimuli ◽  
3D Shapes

Soft materials with programmability have been widely used in drug delivery, tissue engineering, artificial muscles, biosensors, and related biomedical engineering applications. Liquid crystal elastomers (LCEs) can easily morph into three-dimensional (3D) shapes by external stimuli such as light, heat, and humidity. In order to program two-dimensional (2D) LCE sheets into desired 3D morphologies, it is critical to precisely control the molecular orientations in LCE. In this work, we propose a simple photopatterning method based on a maskless projection display system to create spatially varying molecular orientations in LCE films. By designing different synchronized rotations of the polarizer and projected images, diverse configurations ranging from individual to 2D lattice of topological defects are fabricated. The proposed technique significantly simplified the photopatterning procedure without using fabricated masks or waveplates. Shape transformations such as a cone and a truncated square pyramid, and functionality mimicking the responsive Mimosa Pudica are demonstrated in the fabricated LCE films. The programmable LCE morphing behaviors demonstrated in this work will open opportunities in soft robotics and smart functional devices.

Characterization of frozen hydrated biological specimens by low-loss EELS

1992 ◽  
Vol 50 (2) ◽  
pp. 1572-1573
Author(s):  
Songquan Sun ◽  
Richard D. Leapman
Keyword(s):  
Water Content ◽  
Direct Method ◽  
Internal Standard ◽  
Dry Weight ◽  
Dark Field ◽  
Protein Solutions ◽  
Subcellular Compartment ◽  
Differential Shrinkage ◽  
Electron Energy Loss

Analyses of ultrathin cryosections are generally performed after freeze-drying because the presence of water renders the specimens highly susceptible to radiation damage. The water content of a subcellular compartment is an important quantity that must be known, for example, to convert the dry weight concentrations of ions to the physiologically more relevant molar concentrations. Water content can be determined indirectly from dark-field mass measurements provided that there is no differential shrinkage between compartments and that there exists a suitable internal standard. The potential advantage of a more direct method for measuring water has led us to explore the use of electron energy loss spectroscopy (EELS) for characterizing biological specimens in their frozen hydrated state.We have obtained preliminary EELS measurements from pure amorphous ice and from cryosectioned frozen protein solutions. The specimens were cryotransfered into a VG-HB501 field-emission STEM equipped with a 666 Gatan parallel-detection spectrometer and analyzed at approximately −160 C.

A Simple Real-Space Channelling Theory for Electron Diffraction and HREM

1990 ◽  
Vol 48 (1) ◽  
pp. 64-65
Author(s):  
D. Van Dyck
Keyword(s):  
High Resolution ◽  
Electron Diffraction ◽  
Direct Method ◽  
Real Space ◽  
Zone Axis ◽  
Phase Object ◽  
High Resolution Images ◽  
The Many ◽  
Analytical Expressions ◽  
Electron Wavefunction

The computation of the many beam dynamical electron diffraction amplitudes or high resolution images can only be done numerically by using rather sophisticated computer programs so that the physical insight in the diffraction progress is often lost. Furthermore, it is not likely that in this way the inverse problem can be solved exactly, i.e. to reconstruct the structure of the object from the knowledge of the wavefunction at its exit face, as is needed for a direct method [1]. For this purpose, analytical expressions for the electron wavefunction in real or reciprocal space are much more useful. However, the analytical expressions available at present are relatively poor approximations of the dynamical scattering which are only valid either for thin objects ((weak) phase object approximation, thick phase object approximation, kinematical theory) or when the number of beams is very limited (2 or 3). Both requirements are usually invalid for HREM of crystals. There is a need for an analytical expression of the dynamical electron wavefunction which applies for many beam diffraction in thicker crystals. It is well known that, when a crystal is viewed along a zone axis, i.e. parallel to the atom columns, the high resolution images often show a one-to-one correspondence with the configuration of columns provided the distance between the columns is large enough and the resolution of the instrument is sufficient. This is for instance the case in ordered alloys with a column structure [2,3]. From this, it can be suggested that, for a crystal viewed along a zone axis with sufficient separation between the columns, the wave function at the exit face does mainly depend on the projected structure, i.e. on the type of atom columns. Hence, the classical picture of electrons traversing the crystal as plane-like waves in the directions of the Bragg beams which historically stems from the X-ray diffraction picture, is in fact misleading.

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