Abstract The present research investigates optimizing the impact resistance of functionally graded sandwich structures using experimental and numerical approaches. The low‐velocity impact (LVI) responses of functionally graded sandwich composite (FGSC) with different configurations with skin material jute/rubber/jute (JRJ) and core material having epoxy and sea sand by volume fraction of sea sand at 0%, 10%, 20%, and 30%. Sandwich structures were impacted with LVI (5.89, 10.92, and 15.18 m/s), with the impactor dropped from heights of 0.5, 1, and 1.5 m with precompressed spring loads. FGSC samples are considered a deformable body, and the impactor is modeled as a rigid body using commercially accessible dynamic explicit software. The burn‐out test and weight method were used to test the core's gradience; both methods' results substantially matched, and the variance in gradation could be observed. The proposed sandwich structure characteristics are examined by energy absorption, peak force, energy loss percentage, and coefficient of restitution. Results showed that SC30S provides greater energy absorption and superior damage resistance when tested on LVI. To evaluate the accuracy of experimental findings in predicting the indentation behavior of the sandwich structure, the finite element analysis was used to compare with the experimental results. According to the examination of these proposed FGSC overall performance, they could potentially be employed as sacrificial materials for LVI applications like claddings to shield major structural components. The systematic approach used in this work serves as a standard for choosing and using FGSC effectively for LVI applications. Highlights Low‐velocity impact behavior of sandwich structures was investigated. Combining flexible skin and epoxy core enhances energy absorption. Based on impact energy levels, impact damage areas were determined. Examined sandwich structure advantages in structural and aerospace uses. In terms of time and cost, the numerical analysis method would be useful. 

Experimental and numerical investigation on low‐velocity impact response of sandwich structure with functionally graded core

We designed three‐dimensional (3D) structures through a combination of glass fiber cloth and in situ formation of nano polyphenylene oxide (PPE) fibers during the fabrication process of thermosetting cyanate ester/bismaleimide composites and developed a self‐stitching technique based on PPE fiber and interpenetrating polymer networks (IPNs) for aiding the crack self‐healing. The building of 3D structure effectively improves the interface interaction between fiber and matrix and suppresses the crack propagation process in composite, leading to significant enhancement in the mechanical properties. When PPE content is 20%, the interlaminar shear strength, flexural strength, impact strength, and tensile strength of the resulting composite are 98%, 74%, 95%, and 101% higher than those of the composite without PPE. The resulting composites possess excellent thermomechanical and lower dielectric properties. Because IPNs within composites can create interspaces and easily deform above glass‐transition temperature, PPE components may penetrate through the interspaces under thermal expansion force, and the contraction stresses of polymers generate strong locking effects in composite after cooling to room temperature, then the crack surfaces of composites can be stitched by PPE fibers, significantly recovering the mechanical properties. The healing efficiency of the composite with 30% PPE after impact and then heating at approximately 280°C can reach 96%.
3D structures were constructed during the fabrication process of glass‐fiber‐reinforced thermosetting cyanate ester/bismaleimide composite.
A self‐stitching technique was developed for aiding the crack self‐healing of composite.
3D structures significantly improved the interface interaction between fiber and matrix in laminated composite.
The mechanical properties of the resulting composite could be significantly improved by 3D structures.
The healing efficiency of the healed composite could reach 96%.


Designing a 3D structure and a self‐healing technique for advanced polymer composites with outstanding mechanical properties and healing ability

This work investigates the low‐velocity impact (LVI) and self‐healing behavior of carbon fiber composite laminates interlaced with electrospun polyacrylonitrile core–shell nanofibers (PAN@CFRP). The main goal is to investigate the influence of different stacking configurations of core–shell nanofibers on the impact resistance and self‐healing properties of composite laminates. To achieve the purpose, three different stacking configurations were designed and tested alongside virgin specimens. The damage mechanism and self‐healing of laminates following LVI were determined using ultrasonic C‐scan and cross‐sectional microscopy examinations. At an impact energy of 14.1 J, the flexural strength of the post‐healing PAN‐3@CFRP specimen reached 95.0% of the initial value, whereas at an impact energy of 21.8 J, severe impact damage was observed in the laminates with different configurations. Among the laminates, the PAN‐1@CFRP specimen had the highest flexural strength after healing, which reached 80.1% of its pre‐impact strength. As observed, the impact resistance and self‐healing capacity of composites could be significantly enhanced by optimizing the distribution configuration of core–shell nanofibers for various impact energies.
The introduction of electrospun core–shell nanofibers has not significantly compromised the mechanical properties of the composites, but rather enhanced their toughness.
The addition of core–shell nanofibers significantly enhances the impact resistance of the composites and imparts excellent self‐healing properties to the material.
The flexural strength of impact‐damaged specimens with different stacking configurations can be restored up to 95% of the undamaged specimen after repair treatment.
Significantly improved impact resistance and self‐healing ability of laminates by optimizing the distribution configuration of core–shell nanofibers between composite layers.


Low‐velocity impact response and post‐impact assessment of self‐healing composites with different stacking configurations of core–shell nanofibers

Abstract Strategies for strengthening the characteristics of naturally inspired multilayer composites are being sought, including inorganic platelet alignment, enhancing interlaminar collaboration between polymeric solution and printed platelets, and optimizing soft phase materials. The former tactic is significant because a particle reinforcement can use high in-plane modulus and strength of inorganic mineral bridges and asperities as much as possible. Fly ash is an immense amount of environmental waste from thermal power plants and other industries that can be effectively employed as particle reinforcement in nature-inspired composites. Herein, the study demonstrates an anomalous phenomenon combining soft microscale organic polylactic acid (PLA) components with inorganic micro grains fly ash (FA) hierarchically designed by natural organisms through dual 3D printing technique (fused deposition modeling &amp; direct ink writing). Our investigation of composite deformation reveals that sheet nacreous architecture exhibits the highest flexural and tensile modulus, whereas foliated structure shows better impact resistance. Remarkably, as fly ash filler increases, the mechanical behavior of composites improves as large as 882 MPa and 418 MPa, flexural and elastic modulus, respectively. 

Harnessing Fly Ash as Particle Reinforcement in Nature-Inspired Multilayer Composites

Abstract Drawing inspiration from carp scales to manufacture specimens, we investigated the effect of embedding aluminum mesh on the two‐point low‐velocity impact (LVI) and compression‐after‐double‐impact (CAI) behavior of glass fiber‐reinforced polymer (GFRP) laminates, fabricated via the hot‐pressing process, varying lay‐up angle of both fiber and aluminum mesh. INSTRON 9340 performs LVI loading tests at the same impact distance and with four different incidence energies. Further, in addition to their post‐impact damage characterized by an ultrasonic C‐scan, their failure evolution of compression after impact was presented according to strain contour obtained from the digital image correlation (DIC) and scanning electron microscope (SEM) technique. After comparing the response history and damage morphology of various panels, it was found that the addition of aluminum mesh could improve the ductility of the panels and promote their performance in low‐velocity impact events. This enhancement stems from the ability of the ductile aluminum mesh net to effectively absorb and redistribute impact energy in the vicinity of the impact point. It is noteworthy that the damaged area of specimens with different layup angles following low‐velocity impact exhibits the following pattern: VG8VAl &gt; VG8IAl &gt; IG8IAl. Highlights Mechanical behavior on two‐point LVI test of laminates varying layup angles. The LVI and CAI performance was analyzed by C‐scan, SEM, and DIC. Compressive failure mode is brittle fracture at the impact area. The resin fills holes in the aluminum mesh to improve sample impact property. Laminates with aluminum mesh have less damage but a larger damage area. 

Experimental investigation on the compression‐after‐double‐impact behaviors of <scp>GFRP</scp> laminates embedded with aluminum mesh

Exploration of impact response and damage mechanism of discontinuous CFRP laminates subjected to low velocity impact

Since the advent of semiconductor detectors, they have been developed for several generations, and their performance has been continuously improved. In this paper, we propose a new silicon drift detector structure that is different from the traditional spiral SDD structure that has a gap between the cathode ring and the width of cathode ring, increasing gradually with the increase of the radius of the cathode ring. Our new structure of spiral SDD structure has equal cathode ring gap and a given surface electric field, which has many advantages compared with the traditional structure. The novel SDD structure controllably reduces the area of silicon oxide between the spiral rings, which in turn reduces the surface leakage current due to the reduction of total oxide charge in the silicon oxide and electronic states on the silicon/silicon oxide interface. Moreover, it has better controllability to adjust this spiral ring cathode gap to achieve better surface electric field distribution, thus realizing the optimal carrier drift electric field and achieving the optimal detector performance. In order to verify this theory, we have modeled this new structure and simulated its electrical properties using the Sentaurus TCAD tool. We have also analyzed and compared different spiral ring cathode gap structures (from 10 µm to 25 µm for the gap). According to the simulation results of potential, electric field, and electron concentration, we have obtained that a spiral ring cathode gap of 10 µm has the best electrical characteristics, more uniform distribution of potential and surface electric field, and a more smooth and straight electron drift channel.

/pdf/novel-spiral-silicon-drift-detector-with-equal-cathode-ring-25a4bwdz.pdf

Novel Spiral Silicon Drift Detector with Equal Cathode Ring Gap and Given Surface Electric Fields

In our previous studies, the silicon drift detector (SDD) structure with a constant spiral ring cathode gap (g) and a given surface electric field has been partially investigated based on the physical model that gives an analytical solution to the integrals in the calculations. Those results show that the detector has excellent electrical characteristics with a very homogeneous carrier drift electric field. In order to cope with the implementation of the theoretical approach with a complete set of technical parameters, this paper performs different theoretical algorithms for the technical implementation of the detector performance using the Taylor expansion method to construct a model for cases where the parameter “j” is a non-integer, approximating the solution with finite terms. To verify the accuracy of this situation, we performed a simulation of the relevant electrical properties using the Sentaurus TCAD tool 2018. The electrical properties of the single and double-sided detectors are first compared, and then the effects of different equal gaps g (g = 10 μm, 20 μm, and 25 μm, respectively) on the electrical properties of the double-sided detectors are analyzed and demonstrated. By analyzing and comparing the electrical characteristics data from the simulation results, we can show that the double-sided structure has a larger transverse drift electric field, which improves the spatial position resolution as well as the response speed. The effect of the gap size on the electrical characteristics of the detector is also analyzed by analyzing three different gap bifacial detectors, and the results show that a 10 μm equal gap is the optimal design. Such results can be used in applications requiring large-area SDD, such as the pulsar X-ray autonomous navigation. in the future to provide navigation and positioning space services for spacecraft deep-space exploration.

Optimized Design of a Hexagonal Equal Gap Silicon Drift Detector with Arbitrary Surface Electric Field Spiral

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Exploration of impact response and damage mechanism of discontinuous CFRP laminates subjected to low velocity impact

Novel Spiral Silicon Drift Detector with Equal Cathode Ring Gap and Given Surface Electric Fields

Optimized Design of a Hexagonal Equal Gap Silicon Drift Detector with Arbitrary Surface Electric Field Spiral