Search

Ceramic matrix composites have garnered significant attention in aerospace and other fields due to their outstanding properties. However, as a common and critical defect, density defect often results in non-uniform matrix distribution and internal pore formation, posing a substantial risk to component safety. This paper presents a novel method aimed at deliberately inducing varying degrees of density defects in SiC f /SiC. The feasibility of this method is validated using infrared thermography and computed tomography. As density defects aggravate, the porosity of the sample's defective region gradually increases, with both the number of micropores and the dimensions of larger pores expanding. This trend underscores the decreased compactness of the SiC matrix. Additionally, there is an initial decline in tensile strength followed by stabilization, while the tensile elastic modulus exhibits a continued decrease. The retention rates of the minimum tensile strength and tensile elastic modulus are 83.89 % and 64.77 %, respectively, compared to those of the defect-free samples. In terms of compressive properties, both compressive strength and compressive elastic modulus exhibit progressive decreases, culminating in final retention rates of 76.54 % and 72.02 %, respectively. Density defects reduce the matrix cracking stress and introduce new defects such as delamination, thereby altering the material's damage mechanism. This study provides innovative perspectives for risk assessment and lifespan prediction of density defects, especially concerning more complex components like turbine blades. • Artificial defects containing locally varying density values are controlled in SiC f /SiC for the first time. • Tensile strength demonstrates higher tolerance to more severe density defects than compressive strength. • Evaluating density defects by correlating pore geometry with material mechanical properties offers a novel approach. [ABSTRACT FROM AUTHOR]

The use of Textile-Reinforced-Matrix (TRM) systems is gaining consensus as a possible technical solution for strengthening masonry structures. In this context, the use of natural fabrics (among which those made of flax) instead of synthetic ones can have a positive impact on several sustainability-related aspects, such as renewability, recyclability, biodegradability, low price. However, both mechanical properties and durability performance of natural fibres and fabrics needs to be further investigated with the aim to make it possible their use in composites for construction. Furthermore, this paper reports the results of a fundamental study on a bidirectional flax fabric eventually intended as the reinforcement in cement-based composite systems. Specifically, it aims at determining the tensile strength of flax of fibres, threads and the fabrics, and investigating how they are influenced by various environmental exposures and aging processes. The results in the experimental tests reported herein show that fibres and fabrics suffered no significant reduction in tensile strength due to the considered environmental exposure. Despite the common belief that natural fibres may be affected by durability issues, the results demonstrate that the flax fabric under investigation can be utilised as a reinforcement in TRM systems, which is the main novelty and original contribution of this paper. [ABSTRACT FROM AUTHOR]

Abstract Fiber-Reinforced Polymer (FRP) represents one of the most diffuse and effective strengthening technique for retrofitting columns in existing buildings when presenting insufficient mechanical properties. In fact, the confinement effect provided by wraps with high-tensile strength and stiffness induces significant enhancement of the mechanical behaviour. In this paper experimental results of axial compression tests on both un-confined and FRP-confined prismatic yellow tuff masonry columns are presented. In particular, two types of masonry arrangements, regular and irregular, were reproduced in order to investigate the effectiveness of the confinement on column typologies widely used in the past in Southern Italy and Mediterranean basin. The performed experimental tests allowed to obtain the constitutive axial and transversal stress-strain laws and to evaluate the improvement of the mechanical behaviour, in terms of strength and ductility, due to FRP confinement. The results have highlighted a significant difference in the shape of the constitutive law for confined masonry with respect to the one of confined concrete. Contrary to FRP confined concrete members, in the case of confined masonry members specific theoretical constitutive model has been not yet developed. To this aim, in this paper the various stress-strain laws developed for FRP-confined concrete elements has been applied to masonry elements too and a comparative analyses between experimental and theoretical results has been carried out. [ABSTRACT FROM AUTHOR]

A kind of epoxidized natural rubber (ENR)/CNCs composites without using conventional crosslinking agents was successfully fabricated in this paper, in which a supramolecular network based on hydrogen bonds is formed. FTIR confirmed that parts of hydroxyl groups of CNCs reacted with the epoxy group of ENR and hydrogen bonds were developed between CNCs and ENR. This made CNCs involve in the formation of supramolecular network, effectively improving the mechanical properties and endowing the ENR/CNCs composites with superior self-healing capacity simultaneously. The tensile strength of ENR/CNCs composites with 20 wt% CNCs rises to 1.19 MPa, almost 2 times than that of the neat ENR. Importantly, the ENR/CNCs composite with a filler loading of 20 wt% exhibits impressive self-healing efficiency of 83% of the its original strength and 95% of the original extensibility without any external stimulus at room temperature. Healing behavior is strongly influenced by CNCs contents, healing temperature, healing time and its times. [ABSTRACT FROM AUTHOR]

In the typical structures of carbon-fibre-reinforced plastics (CFRP), multiple layers are stacked together with a particular sequence in order to give specific mechanical characteristics. Layers are organized with different angles, different sequences and different technological processes to obtain innovative materials. This paper introduces a new parameter, able to improve mechanical properties of composites. It analyses an unconventional fibres orientation combined with the through-the-thickness stitching on the in-plane mechanical properties of CFRP. Conventional carbon fibres orientation is generally referred to a Cartesian coordinate system, in which fibres are arranging in bundles along different angle orientations respect to the zero lamina. In this paper a polar coordinate system of continue carbon tow is introduced to create specimens as well as complex geometry components in an easy way. Five different configurations are studied: two are classified as traditional composites (unstitched and Cartesian orientation of woven carbon cloth), three are defined as innovative composites (stitched laminates and continue carbon tow organized in polar or Cartesian system). The application of this technique aims to introduce some advantages in the material's manufacturing process and if compared with the conventional strategy seems to be very promising since it appears to be very efficient in stopping delamination phenomenon. [ABSTRACT FROM AUTHOR]

Abstract The present paper is dealing with the reinforcement of epoxy and high density polyethylene (HDPE) matrices using stainless steel flakes (SSFs). Particulate composite specimens of different wt SSFs contents up to 10% were produced for each case of polymer matrix. The so-obtained SSFs/epoxy and SSFs/HDPE composites underwent tensile, three-point bending and compression tests. The tensile and flexural performance of the composites of both matrices seemed to be negatively affected by the SSF loading. However, the response on plastic deformation under tensile loading for the SSFs/HDPE composites was considerably enhanced for low SSFs contents. The compression response was enhanced in the case of SSFs/HDPE composites as well. The tensile, flexural and compression performance is being explained on the basis of the microstructural observations for each case of reinforced matrix. [ABSTRACT FROM AUTHOR]

Abstract In recent years, the use of industrial by-products and waste-based materials in the construction industry has received significant attention to develop eco-friendly and greener construction materials with the aim of reducing the impact of construction industry on the environment. The development of new concretes where cement is replaced with industrial by-products, such as ground granulated blast furnace slag (GGBS) and fly ash (FA), and natural sand (NS) is replaced with waste-based sands, such as lead smelter slag (LSS) and glass sand (GS), would lead to enormous environmental and health benefits by enabling the use of abundant wastes, reducing the extraction of non-renewable natural resources, and reducing the CO 2 emissions associated with concrete production. This paper presents an experimental study on the properties of geopolymer mortars prepared with FA/GGBS, LSS, and GS under ambient curing condition. A total of 12 batches of geopolymer mortars were manufactured and experimental tests were conducted to determine the flowability, hardened density, compressive strength, direct tensile strength, water absorption, and drying shrinkage of each batch together with the alkali-silica reaction (ASR) expansion of batches containing GS. Microstructural analysis was undertaken to describe the reasons for the obtained experimental results. The results show that the compressive and tensile strength of geopolymer mortars increase with an increase in the amount of GGBS. The results also show that an increase in the GGBS amount leads to a decrease in the water absorption of geopolymer mortars. Owing to the lower void amount at the binder-sand interaction zones, LSS- and GS-based geopolymer mortars containing up to 50% GGBS exhibit superior mechanical properties compared to those of their NS-based counterparts. These highly promising findings suggest that the full replacement of NS by LSS and GS can provide an attractive avenue to reduce the environmental impact of abundant waste products and conserve non-renewable natural resources. [ABSTRACT FROM AUTHOR]

Abstract To overcome the shortness of organic bonding in fiber-reinforced polymer (FRP) retrofitting, textile-reinforced mortar (TRM) has been studied as an alternative composite for retrofitting structural concrete. However, the brittleness of mortar brings the conflict between the efficient using of FRP and durability performance of TRM. To solve this problem, Engineering Cementitious Composite (ECC) can potentially be used to replace mortar in TRM, due to its "ductile" property. The new textile-reinforced composite is named as TR-ECC. In this paper, the tensile failure mechanism and mechanical properties of TR-ECC composite, which was composed of basalt textile grids and one kind of ECC, Ultra High Ductility Cementitious Composite (UHDCC) as the matrix, was investigated. The uniaxial tensile tests on 24 TR-ECC specimens (eight groups) were carried out. The variables include thickness of UHDCC per layer, textile grid geometry configuration and volumetric ratio of textile grids. The influence of variables on the failure pattern, initial elastic and hardening modulus, crack tensile stress, ultimate tensile strain and stress of TR-ECC were analyzed. Finally, the stress-strain behavior and strength of TR-ECC were compared with that of traditional TRM. The test and comparison results show that ECC can largely improve the textile reinforcement effect than the mortar and well control the cracking width. [ABSTRACT FROM AUTHOR]

Abstract Geopolymer mortar refers to the mortar manufactured with sand and geopolymer, which is composed by the base materials containing affluent aluminium and silicon that was activated by adopting alkaline solution to serve as a binder. The investigation of the properties and application of the geopolymer mortar has attracted more and more attention of the researchers and cement based industries because of its sustainability advantages. This study reviews the properties of the geopolymer mortars including fresh performance (workability, setting time, and temperature of fresh mortar), physical properties, mechanical properties (compressive strength, tensile strength, elastic properties, flexural performance, bonding behavior, and fracture behavior), durability properties (acid resistance, resistance to elevated temperature, frost resistance, water absorption, and shrinkage properties) and microstructure analysis. This study also reviews the properties of different types of geopolymer mortars prepared using various source materials as base materials. The current study results indicate that the geopolymer mortar has exhibited significant feasibility and application prospect to be used as an environmental friendly building material, which may be an appropriate replacement to the traditional cement mortar in the future. Highlights • 119 papers are reviewed on the properties of geopolymer mortars. • Fresh and physical properties of geopolymer mortars are discussed. • Mechanical properties and durability of geopolymer mortars are also addressed. • Microstructure analysis of geopolymer mortars is reviewed. [ABSTRACT FROM AUTHOR]

Abstract This paper presents an experimental/analytical investigation to examine the feasibility of hybrid fibers in self-consolidating concrete containing different fiber types (industrial steel fiber, recycled steel fibers, and Polypropylene fiber), contents (0.5%, 0.75%, 1%, 1.5% in Vol.), and combinations (as single and blended fibers). Fresh and hardened properties of the fiber reinforced self-consolidating concrete were assessed, considering total fiber volume fraction of 1.5%. The fresh state properties were assessed in terms of flow slump diameter and T 500. Moreover, the hardened state properties of specimens were characterized by using the ultrasonic pulse velocity, the compressive strength, the splitting tensile strength, the flexural strength, and the impact resistance. Then, a statistical method based two-parameter Weibull and an optimization procedure were executed on the collected experimental results. The results showed an enhancement of mechanical properties and impact resistance in self-consolidating concrete by the addition of fiber, which was significantly governed by fiber type, content, and combination. Moreover, the optimization procedure revealed that the best performance in terms of maximum mechanical properties and impact resistance, as well as the minimum cost, was achieved in the mixture reinforced with 1.5% recycled steel fiber (Rst1.5) as mono-fiber and the mixture reinforced with 1% industrial steel fiber and 0.5% recycled steel fiber (St1Rst0.5) as hybrid fiber. In addition, the statistical study showed that the two-parameter Weibull could be adopted to analyze the distribution of the first crack (FC) and ultimate crack (UC) impact resistance. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

In this paper, an experimental study has been performed on thick, ±55° filament wound glass/epoxy tubes using quasi-static tests to examine their offshore applications. A new design for the experimental test is developed in which the end tabs and fixture system are made in a way that the stress concentration at the edges of the composite pipe can be reduced. Split disk uniaxial tensile test has been performed on composite pipes with 86 mm of the internal diameter and the thickness of 6.2 mm, in order to evaluate the mechanical properties and to quantify the effect of geometric non-linearities. These pipes can be subjected to different phenomena which can result in introducing a defect in the structure. Two types of pipe specimens are tested which include the composite with notch and the other without notches. The objective of the using a notched specimen is to examine the evolution of the damage and to study the mechanical properties as a function of this damage. The experimental results are described as the influence of the number and the size of notches on the mechanical behavior. These results have shown that the yield stress decreases and yield strain increase with increasing of the notch size and number. The evolution of damage showed that the presence of notches plays an unfavorable role in the integrity of the structure. [ABSTRACT FROM AUTHOR]

Composites utilising long fibres as reinforcement are the most effective from the point of view of the toughening effect. A brittle matrix reinforced by brittle fibres was investigated in this work. Polysiloxane resin was used as matrix precursor in the studied composite, while continuous basalt fibres served as reinforcement. An optimised pyrolysis process conducted at 650 °C under nitrogen atmosphere turned the polymeric precursor into the so-called hybrid matrix consisting of nano-domains of pyrolytic SiOC glass and of non-transformed polysiloxane polymer. The pyrolysis temperature of 650 °C was found to be optimal, resulting in the fracture toughness attacking the level of 20 MPa m 1/2 and the strength reaching the value of 1 GPa. The main aim of this paper is to investigate microstructural changes occurring during long-term (1000 h = 41.7 days) exposition to an oxidative air atmosphere at temperatures from 250 °C to 600 °C and to describe the effect on the mechanical properties of the studied hybrid-matrix composite. The increasing exposition temperature leads to a significant embrittlement of the composite, while the elastic properties (modulus) remain unchanged. Chemical or microstructural changes in the basalt fibres were not detected after the long-term exposition to the tested high temperatures. Nevertheless, fibre embrittlement can be estimated from the tests. Both matrix and fibre-matrix interface were found to suffer from the applied exposition. Distinct changes in chemical composition as well as in microstructure were observed for the matrix. Hence, the observed embrittlement of the composite can be ascribed partly to the changes in the hybrid matrix and the fibre-matrix interface, and partially to fibre embrittlement. [ABSTRACT FROM AUTHOR]

The present paper is dealing with the reinforcement of high density polyethylene (HDPE) matrix using pre-dried graphene nanoplatelets (GNPs). Nanocomposites of three different wt GNPs contents, i.e. 1%, 2% and 3%, were produced. The so-obtained extruded GNPs/HDPE nanocomposites underwent both tensile and three-point bending tests. Ultimate tensile strength was not affected by the GNPs content. However, the response on plastic deformation under tensile loading differed in each case, depending on the microstructure of the produced nanocomposites. Due to the weak Van der Waals forces that bond the graphene layers into a GNP, these layers are allowed to slip in the in-plane level and they were observed dislocated after tensile loading. Pores with high GNPs concentration were detected for GNPs contents greater than 1%. The flexural response was enhanced and flexural strength values were also correlated with the dimensions of the pores formed. [ABSTRACT FROM AUTHOR]

HPFRC/UHPC are today widely applied as repair and reinforcement materials for structures. One of the drawback of commercial HPFRC/UHPC is that any modification of the matrix-fibers mix design, due to the market requirements, affects the mechanical properties of the hardened concrete and therefore the data obtained testing the previous version of the concrete are useless. Prediction models that link the properties of both fibers and matrix to the performances of the hardened concrete are of great practical interest. This paper present a simple and effective model to account for the effect of fibers on the compressive and tensile strengths of HPFRCs as the aspect ratio and volume of fibers changes, extending the range of application of the few existing models. [ABSTRACT FROM AUTHOR]

The paper reports manufacturing of a multi-layer graphene embedded composite of aluminium alloys by direct exfoliation of graphite into graphene with the help of Friction Stir Alloying (FSA). The formation of this nano-composite and optimization of the process parameters led to an approximately two-fold increase in the strength, without loss in ductility, due to the dispersion of the graphene in aluminium. The manufacturing process is scalable and cost effective as it uses graphite powder and aluminium sheets as the raw materials. The presence of graphene layers in the metal matrix was confirmed using Raman spectroscopy as well as TEM. The graphene sheet thickness was measured using AFM after extracting it from the composite. Molecular dynamic simulation results reveal the evolution of newer structures and defects that have resulted in the enhanced properties of the nano-composite. These findings open up newer possibilities toward efficient and scalable manufacturing of high-strength high-ductility metal matrix based graphene nano-composites. [ABSTRACT FROM AUTHOR]

Present paper investigates the simulation of quasi-static response of fabric materials subjected to uniaxial tensile loading. The purpose of this research is to simulate the fabrics mechanical behavior accurately determining the quasi-static elastic and failure properties of fabric yarn and to rank, from the analysis point of view, the parameters which influence the fabric behavior. In particular, a meso-scale approach was employed to model the behavior of different para-aramid fabrics using LS-DYNA software whereas the Nelder & Mead Simplex optimization algorithm was implemented for the determination of material model's parameters by the fitting of numerical and experimental tensile loading curve. [ABSTRACT FROM AUTHOR]

Fused Deposition modelling (FDM) is one of the additive manufacturing (AM) technologies used extensively for modelling and prototyping applications. In commercial FDM setup, filament wire is uncoiled from wire spools and plastic based material is supplied to produce the part. The application area of FDM is limited presently due to selective material availability in market. Some researchers have highlighted the use of reinforced composite wires as FDM filament. But hitherto no work has been reported on the effect of Single particle size (SPS), Dual particle size (DPS), Triple particle size (TPS) of Al 2 O 3 (as reinforcement) in Nylon-6 matrix to be used as feed stock filament for FDM. In this paper, effect of SPS, DPS, and TPS of Al 2 O 3 (as reinforcement) in Nylon-6 matrix on mechanical properties (like: percent age elongation, tensile strength, yield strength, Young's modulus) has been studied. Further, empirical relations have been developed for above mentioned properties and a surface characteristic of developed wires has been observed with SEM image. [ABSTRACT FROM AUTHOR]