Soft composite solids are made of inclusions dispersed within soft matrices. They are ubiquitous in nature and form the basis of many biological tissues. In the field of materials science, synthetic ...soft composites are promising candidates for building various engineering devices due to their highly programmable features. However, when the volume fraction of the inclusions increases, predicting the mechanical properties of these materials poses a significant challenge for the classical theories of composite mechanics. The difficulty arises from the inherently disordered, multi-scale interactions between the inclusions and the matrix. To address this challenge, we systematically investigated the mechanics of densely filled soft elastomers containing stiff microspheres. We experimentally demonstrate how the strain-stiffening response of the soft composites is governed by the critical scalings in the vicinity of a shear-jamming transition of the included particles. The proposed criticality framework quantitatively connects the overall mechanics of a soft composite with the elasticity of the matrix and the particles, and captures the diverse mechanical responses observed across a wide range of material parameters. The findings uncover a novel design paradigm of composite mechanics that relies on engineering the jamming properties of the embedded inclusions.
The intensity gradient method (G2 method), namely computing the light intensity gradient-squared, is a widely used non-invasive experimental method to extract stress information from ...quasi-two-dimensional photoelastic granular materials. Previous works show that calibrated G2 is an accurate measure of global stress. However, whether it can be used at the particle scale aside from the special case of diametric loading remains unclear. We test here the applicability and limitations of G2 as particle scale stress indicator and specify its dependence on relevant experimental parameters of the particles, light conditions, and imaging system. We first propose an explicit formula to calculate the relationship between the G2 value and stress based on the linear elasticity and photoelasticity theories, and then validate our formula by numerical and experimental tests. We find that G2 is proportional to ∑ i F ⃗ i , the sum of magnitudes of the contact forces, for disc particles when forces are not large. We also observe that, for large enough resolution, G2 does not change with the number of contacts as well as the direction of the contact forces under same ∑ i F ⃗ i value. However, we find that this relation between G2 and ∑ i F ⃗ i is not universal for any particle shape. As an example, we show that a square particle can have dramatically different values of G2 under the same contact forces with different contact types (point-edge contact and edge-edge contact).
A photoelastic material will reveal its internal stresses when observed through polarizing filters. This eye-catching property has enlightened our understanding of granular materials for over half a ...century, whether in the service of art, education, or scientific research. In this review article in honor of Robert Behringer, we highlight both his pioneering use of the method in physics research, and its reach into the public sphere through museum exhibits and outreach programs. We aim to provide clear protocols for artists, exhibit-designers, educators, and scientists to use in their own endeavors. It is our hope that this will build awareness about the ubiquitous presence of granular matter in our lives, enlighten its puzzling behavior, and promote conversations about its importance in environmental and industrial contexts. To aid in this endeavor, this paper also serves as a front door to a detailed wiki containing open, community-curated guidance on putting these methods into practice (Abed-Zadeh et al. in Photoelastic methods wiki
https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/home
, 2019).
Water supply services (WSSs) are critical to human survival and development. The Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) model enables an integrated, dynamic, and visual ...assessment of ecosystem services at different scales. In addition, Geodetector is an effective tool for identifying the main driving factors of spatial heterogeneity of ecosystem services. Therefore, this article takes the Three Gorges Reservoir Area (TGRA), the most prominent strategic reserve of freshwater resources in China, as the study area and uses the InVEST model to simulate the spatiotemporal heterogeneity of the supply-demand balance of WSSs and freshwater security patterns in 2005, 2010, 2015, and 2018, and explores the key driving factors of freshwater security index (FSI) with Geodetector. The total supply of WSSs in the TGRA decreased by 1.05% overall between 2005 and 2018, with the head and tail areas being low-value regions for water yield and the central part of the belly areas being high-value regions for water yield. The total demand for WSSs in the TGRA increased by 9.1%, with the tail zones and the central part of the belly zones being the high water consumption areas. In contrast, the head zones are of low water consumption. The multi-year average FSI of the TGRA is 0.12, 0.1, 0.21, and 0.16, showing an upward trend. The key ecological function areas in the TGRA are high-value FSI regions, while the tail zones in the key development areas are low-value FSI regions. Industrial water consumption significantly impacts FSI, with a multi-year average q value of 0.82. Meanwhile, the q value of industrial and domestic water consumption on FSI in 2018 increased by 43.54% and 30%, respectively, compared with 2005. This study analyzes the spatiotemporal variation of WSSs and detects the drivers in the natural-economic-social perspective and innovation in ecosystem services research. The study results can guide water resource security management in other large reservoirs or specific reservoir areas.
Dry granular materials, such as sand, gravel, pills, or agricultural grains, can become rigid when compressed or sheared. Under isotropic compression, the material reaches a certain jamming density ...and then resists further compression. Shear jamming occurs when resistance to shear emerges in a system at a density lower than the jamming density. Although shear jamming is prevalent in frictional granular materials, their stability properties are not well described by standard elasticity theory and thus call for experimental characterization. We report on experimental observations of changes in the mechanical properties of a shear-jammed granular material subjected to small-amplitude, quasistatic cyclic shear. We study a layer of plastic disks confined to a shear cell, using photoelasticimetry to measure all interparticle vector forces. For sufficiently small cyclic shear amplitudes and large enough initial shear, the material evolves to an unexpected “ultrastable” state in which all the particle positions and interparticle contact forces remain unchanged after each complete shear cycle for thousands of cycles. The stress response of these states to small imposed shear is nearly elastic, in contrast to the original shear-jammed state.
Accurate and rapid detection of tea shoots within the tea canopy is essential for achieving the automatic picking of famous tea. The current detection models suffer from two main issues: low ...inference speed and difficulty in deployment on movable platforms, which constrain the development of intelligent tea picking equipment. Furthermore, the detection of tea canopy shoots is currently limited to natural daylight conditions, with no reported studies on detecting tea shoots under artificial light during the nighttime. Developing an all-day tea picking platform would significantly improve the efficiency of tea picking. In view of these problems, the research objective was to propose an all-day lightweight detection model for tea canopy shoots (TS-YOLO) based on YOLOv4. Firstly, image datasets of tea canopy shoots sample were collected under low light (6:30–7:30 and 18:30–19:30), medium light (8:00–9:00 and 17:00–18:00), high light (11:00–15:00), and artificial light at night. Then, the feature extraction network of YOLOv4 and the standard convolution of the entire network were replaced with the lightweight neural network MobilenetV3 and the depth-wise separable convolution. Finally, to compensate for the lack of feature extraction ability in the lightweight neural network, a deformable convolutional layer and coordinate attention modules were added to the network. The results showed that the improved model size was 11.78 M, 18.30% of that of YOLOv4, and the detection speed was improved by 11.68 FPS. The detection accuracy, recall, and AP of tea canopy shoots under different light conditions were 85.35%, 78.42%, and 82.12%, respectively, which were 1.08%, 12.52%, and 8.20% higher than MobileNetV3-YOLOv4, respectively. The developed lightweight model could effectively and rapidly detect tea canopy shoots under all-day light conditions, which provides the potential to develop an all-day intelligent tea picking platform.
The integrity and health of the ecosystem is the material basis for the common prosperity of different minority areas. Since the acceleration of social and economic growth in the 21st century, ...excessive social development has caused ecological imbalance, climate change and environmental pollution and other problems. The irrational use of natural resources gradually affects the balance between man and nature. In this paper, the characteristics of ecosystem health and four sub-systems of environment, economy, society and management in the Three Gorges Reservoir area are selected to study. The purpose of this paper is to construct an ecosystem health evaluation index system to describe the characteristics of the ecosystem in the Three Gorges Reservoir area. Firstly, a multi-criteria evaluation model was established based on catastrophe theory to evaluate the health of the ecosystem in the Three Gorges Reservoir area. Secondly, the Catastrophe progression method (CPM) was used to describe the overall change trend of the ecosystem in the Three Gorges Reservoir area from 2000 to 2016. The study shows that since 2000, with the development of economy and society and the further strengthening of environmental management, the health of the ecosystem in the Three Gorges Reservoir area has been improved year by year. At the same time, in order to further explore the factors affecting the ecosystem health of the reservoir, the climate factors were added to the control variables, and the model regression analysis was established through panel data. The final conclusion was that the average temperature, rainfall and sunshine time had significant effects on the ecosystem of the reservoir.
In a recent paper (Zhao et al., Phys Rev X, 2022, 12: 031,021), we reported experimental observations of “ultrastable” states in a shear-jammed granular system subjected to small-amplitude cyclic ...shear. In such states, all the particle positions and contact forces are reproduced after each shear cycle so that a strobed image of the stresses and particle positions appears static. In the present work, we report further analyses of data from those experiments to characterize both global and local responses of ultrastable states within a shear cycle, not just the strobed dynamics. We find that ultrastable states follow a power-law relation between shear modulus and pressure with an exponent
β
≈ 0.5, reminiscent of critical scaling laws near jamming. We also examine the evolution of contact forces measured using photoelasticimetry. We find that there are two types of contacts: non-persistent contacts that reversibly open and close; and persistent contacts that never open and display no measurable sliding. We show that the non-persistent contacts make a non-negligible contribution to the emergent shear modulus. We also analyze the spatial correlations of the stress tensor and compare them to the predictions of a recent theory of the emergent elasticity of granular solids, the Vector Charge Theory of Granular mechanics and dynamics (VCTG) (Nampoothiri et al., Phys Rev Lett, 2020, 125: 118,002). We show that our experimental results can be fit well by VCTG, assuming uniaxial symmetry of the contact networks. The fits reveal that the response of the ultrastable states to additional applied stress is substantially more isotropic than that of the original shear-jammed states. Our results provide important insight into the mechanical properties of frictional granular solids created by shear.
The jamming behavior of a system composed of discs has been well documented. However, it remains unclear how a granular system consisting of non-spherical particles transitions between unjammed and ...jammed states. Here, we present compression experiments to study the jamming transition of 2D granular materials composed of photoelastic heptagonal particles and compare these results to data for discs and pentagons. We determine the critical packing fraction of heptagons and make a comparison to discs and pentagons. In the experiment, we subject 618 heptagonal particles to cyclic compression. We track the motion (inlcuding rotations) of the particles, and we measure forces on particles by photoelasticity. We observe a power law relationship between the average contact number (Z) and the pressure (P). Furthermore, we classify the type of contacts by the relative orientation of pairs of contacting particles (creating point-to-face and face-to-face contacts), and we explore the evolution of the contacts during jamming.
We present a novel Couette shear apparatus capable of generating programmable azimuthal strain inside 2D granular matter under Couette shear. The apparatus consists of 21 independently movable ...concentric rings and two boundary wheels with frictional racks. This makes it possible to quasistatically shear the granular matter not only from the boundaries but also from the bottom. We show that, by specifying the collective motion of wheels and rings, the apparatus successfully generates the desired strain profile inside the sample granular system, which is composed of about 2000 photoelastic disks. The motion and stress of each particle is captured by an imaging system utilizing reflective photoelasticimetry. This apparatus provides a novel method to investigate shear jamming properties of granular matter with different interior strain profiles and unlimited strain amplitudes.
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