Stretchable strain sensors have promising potentials in wearable electronics for human motion detection, health monitoring and so on. A reliable strain sensor with high flexibility and good stability ...should be designed to detect human joints motions with a large deformation. Here, a simple and facile solution mixing-casting method was adopted to fabricate a highly stretchable strain sensor based on composites mixing polydimethylsiloxane (PDMS) with hybrid carbon nanotubes (CNTs) and carbon black (CB) conductive nanofillers (CNTs-CB). Bridged and overlapped hybrid CNTs-CB nanofillers structure was achieved in the composite on the basis of the morphology observation. In monotonic stretching test, the CNTs-CB/PDMS composites strain sensors exhibited high stretchability, strain-dependent sensitivity in a wide strain sensing range (ca. 300% strain) and an excellent linear current-voltage behavior. During stretching-releasing cycles, the strain sensors presented excellent repeatability, good stability and superior durability (2500 cycles at 200% strain). Combined with the above outstanding strain sensing performances, the fabricated stretchable strain sensors were attached onto different joints of human body to monitor the corresponding human motions, demonstrating their attractive perspective in large human motions detection.
•Steel–precast UHPC composite beam performs better than conventional counterpart.•Composite beam shows similar load–slip relationship to push-out test with connector fracture.•Rigid plastic analysis ...models are proposed to predict the flexural capacity.
Two types of steel–precast ultra-high-performance concrete (UHPC) composite beams were investigated in this study, which can be vastly used in accelerated bridge construction (ABC). One of them contains full-depth slabs with stud shear connectors embedded in shear pockets, while the remaining one adopts demountable slabs with high-strength friction-grip bolts (HSFGBs). Four-point bending tests were conducted on six large-scale composite beams to investigate the interfacial shear and flexural performance of such innovative types of steel–precast UHPC composite structures. The failure modes, vertical deflection, horizontal interfacial slip and the stain distribution at mid-span cross-section were investigated. The experimental results indicated that the cracking patterns and failure modes of the composite beams were highly dependent on the slab concrete types and the degrees of shear connection. The composite beams adopting UHPC slabs achieved larger cracking resistance and higher ultimate strength than those containing normal-strength concrete slabs and favorable ductility. Similar trends were also presented by the composite beams with large degrees of shear connection. The composite beams with HSFGBs showed enhanced load capacities and larger vertical deflections and horizontal interface slips at peak load than those adopting stud shear connectors. Additionally, the composite beams that failed in shear connector fractures presented shear resistance–interface slip relationships comparable to their push-out counterparts. Finally, theoretical formulas based on rigid plastic analysis were proposed for predicting the flexural capacity of both types of composite beams.
The aim was to evaluate the effect of short glass-fiber/filler particles proportion on fracture toughness (FT) and flexural strength (FS) of an experimental flowable fiber-reinforced composite ...(Exp-SFRC) with two methacrylate resin formulations. In addition, we wanted to investigate how the fracture-behavior of composite restorations affected by FT values of SFRC-substructure.
Exp-SFRC was prepared by mixing 50wt% of dimethacrylate based resin matrix (bisGMA or UDMA based) to 50wt% of various weight fractions of glass-fiber/particulate filler (0:50, 10:40, 20:30, 30:20, 40:10, 50:0wt%, respectively). FT and FS were determined for each experimental material following standards. Specimens (n=8) were dry stored (37°C for 2 days) before they were tested. Four groups of posterior composite crowns (n=6) composed of different Exp-SFRCs as substructure and surface layer of commercial particulate filler composite were fabricated. Crowns were statically loaded until fracture. Failure modes were visually examined. The results were statistically analysed using ANOVA followed by post hoc Tukey’s test.
ANOVA revealed that ratio of glass-fiber/particulate filler had significant effect (p<0.05) on tested mechanical properties of the Exp-SFRC with both monomer systems. Exp-SFRC (50wt%) had significantly higher FT (2.6MPam1/2) and FS (175.5MPa) (p<0.05) compared to non-reinforced material (1.3MPam1/2, 123MPa). Failure mode analysis of crown restorations revealed that FT value of the substructure directly influenced the failure mode.
This study shows that short glass-fibers can significantly reinforce flowable composite resin and the FT value of SFRC-substructure has prior importance, as it influences the crack arresting mechanism.
The goal of our research was to develop a continuous glass fibre-reinforced epoxy matrix self-sensing composite. A fibre bundle arbitrarily chosen from the reinforcing glass fabric in the composite ...was prepared to guide white light. The power of the light transmitted by the fibres changes as a result of tensile loading. In our research, we show that a selected fibre bundle even without any special preparation can be used as a sensor to detect deformation even before the composite structure is damaged (before fibre breaking).
A novel additive manufacturing approach is herein reported for manufacturing high mechanical strength continuous carbon fiber‐reinforced silicon carbide (Cf/SiC) composite materials. Continuous ...carbon fibers were coated with polycarbosilane (PCS) using a colloidal evaporative deposition process and then coextruded with high solid content SiC ink. The zeta potential of the SiC ink was adjusted to optimize the printing ability of the suspension. During sintering, small SiC grains and whiskers were generated in the gaps in and around the PCS‐coated carbon fibers, which led to the improved flexural strength and density of the composites. Meanwhile, the PCS coating on the surface of the carbon fibers prevented the carbon fibers from reacting with SiO gas generated by reactions between the SiC matrix and SiO2 and sintering additives (Al2O3 and Y2O3), effectively preserving the structural integrity of the carbon fibers. Compared to the SiC specimens containing uncoated carbon fibers, the density of the specimens fabricated with coated carbon fibers was increased from 2.51 to 2.85 g/cm3, and the strength was increased from 190 to 232 MPa.
Carbon fibre reinforced polymer (CFRP) composite structures may experience light surface damage such as shallow surface scratch around 50 μm or less in applications. In this study, critical bending ...loads of 2D woven CFRP panels with and without shallow surface scratches were assessed under three-point-bending (3-p-b) conditions and then modelled by a simple strength theory for composite fracture. This closed-form tensile strength solution is a non- Linear Elastic Fracture Mechanics (LEFM) model derived specifically for heterogeneous composites. Direct tensile tests of the CFRP panels (without shallow surface scratch) were also performed, and measured tensile strength was compared with that from 3-p-b tests. The relative error between the two different tests was only around 6.7%. The ply thickness around 140 μm was selected as the controlling composite microstructure parameter or characteristic composite unit Cch in this non-LEFM model. This simple model shows that a suitable composite characteristic microstructure measurement such as Cch = ply thickness can significantly simplify composite fracture analysis. A simple statistical analysis using a 2D normal distribution methodology for strength measurements was also introduced so that the experimental scatters can be analysed. The 95% reliability band can be conveniently used in safe design of composite structures.
The main focus of this review is on soft composites, relatively new to the literature. The ballistic fabrics, mechanism of ballistic energy absorption and parameters affect the ballistic performance ...of fabrics are reviewed. Adding shear thickening fluid (STF) and natural rubber (NR) to fabric and their potential to enhance the impact performance of woven fabrics are considered. Shear thickening mechanism, parameters influence the Shear thickening and impact response of fabric/STF composite are explored. Numerical modelling techniques for the estimation of impact resistance of fabric/STF are outlined. Also the role of shear thickening fluid in energy absorption of fabric/STF composite was investigated. Moreover mechanical and impact characteristics of elastomeric composites which contain one rubbery part as either matrix or completely separate media are explored as well, which have not been considered within previous review papers so far.
Presents the latest strategies in the development and use of composite materials for large structures and the effects of defects Practical Design and Validation of Composites Structures: Effects of ...Defects offers an important guide to the use of fiber-reinforced composites and how they affect the durability and safety of engineering structures such as aircraft, ships, bridges, wind turbines as well as sporting equipment. The text draws on the authors' direct experience in industry and academia to cover the most recent strategies in the development of composite structures and uniquely integrates the assessment of the effects of defects introduced during production. This comprehensive resource builds on an essential introduction to the characteristics of composites and the most common types of defects encountered in production. The authors review the recent manufacturing methods and technologies used for inspecting composite structures and the design issues related to an analysis of their failure and strength incorporating the variability of processing. The text also contains information on the latest regulatory requirements and the relevant standards associated with the testing and design within a robust design philosophy and approach. This important resource: Offers a comprehensive review of the most current regulatory developments in the use of composites for the construction of complex composite structures Presents information on the basic characteristics of composites Includes testing strategies for determining the impacts of production defects Reviews the most current manufacturing methods and inspection technologies in the field Contains methods for statistical analysis and processing of experimental effects of defects test data Written for professional engineers in mechanical engineering, automotive engineering, aerospace engineering, civil engineering, and energy engineering as well as industry and academic researchers, Practical Design and Validation of Composites Structures: Effects of Defects is the hands-on text that covers the essential information needed to understand the use of composites and how they affect complex engineering projects using composites.
Particle-reinforced aluminum matrix composites were produced from powder mixtures of aluminum and silicon by using multiple passages of friction stir processing (FSP). In the composites, the Si ...particles with an average size of ∼1.5
μm are uniformly dispersed in the aluminum matrix which has a fine-grained structure (∼2
μm). The strengthening mechanism of the composites is discussed. It indicates that the fine grain size of aluminum, the Orowan strengthening due to intragranular particles and the dislocations generated by thermal mismatch all contribute significantly to the composite yield strength.
The conventional repairing of CFRP (continuous fiber-reinforced polymer composites) includes complicated steps of patching, splicing, repairing, and post-curing. Intensive labor work needs to be ...conducted, and poor surface quality and weak interfacial adhesion are usually observed. This work mainly introduces an in situ online repairing method using AM (additive manufacturing) facilitated composite fabrication. With the advances of the robotic-assisted AM process, the surface roughness and accuracy during the repairing process can be evaluated online upon layer-by-layer process. In order to fulfill the efficient and on-site requirements for repairing damage in structural components, this study explores the method including in situ repairing, laser point clouds online collection, and repairing path planning based on multi-axial additive manufacturing of composites. A repair algorithm is proposed incorporating point clouds collection, measurement evaluation, and path planning. Furthermore, relevant mechanical measurements have been conducted, so as to assess the interface degree of recovery. A rapid online evaluation and surface conformal repairing method have been proposed to overcome the technical bottleneck of in situ automatic repairing of damaged composites. It expands the application of multi-axial robot-assisted CFRP AM.
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