Composite Strengthening Research Articles

Effect of hemp bio composite strengthening on masonry barrel vaults damage

Masonry vaults are common structural elements of the Italian architectural heritage, significantly vulnerable to seismic loads. For this reason strengthening is often required. In the last decade, the use of traditional reinforcement techniques has been progressively replaced by Fiber Reinforced Polymers (FRP) bonded at the vault extrados/intrados. However, this approach has shown drawbacks mainly associated to the polymeric nature of matrix and physical compatibility between the matrix and the masonry support. Consequently, FRP strengthening evolved to innovative composite materials obtained by cement based matrix, i.e. Fiber Reinforced Cementitious Matrix (FRCM). Moreover, within the growing environmental sustainability issues, the scientific research is focusing on the development of biodegradable composite materials, based on vegetal fibers and natural matrices. This paper presents the results of experimental tests on two full-scale masonry vaults with the same geometry and mechanical properties: one is unreinforced and one is reinforced at the extrados by continuous bidirectional hemp ropes bonded in a layer of cocciopesto matrix (i.e. a mix of ground clay bricks and organic binder). The two models were built and tested in the 3D shaking table system of the Laboratory of Earthquake Engineering and Dynamic Analysis (LEDA) at Enna Kore University. Each vault was subjected to seismic loads and dynamic identification tests: the seismic load was given with increasing amplitude at the base of the two models while the dynamic identification tests were carried out after each seismic sequence in order to evaluate the variation of the dynamic properties, testifying structural damage. The strengthening effectiveness was assessed by comparing the damages detected on the unreinforced and reinforced masonry vaults. Results showed that the proposed bio composite strengthening material is effective for improving the seismic performance of masonry vaults.

A New Method of Strengthening the Compressed Reinforced Concrete Columns Based on the Use of Concrete and Composite Materials

Introduction. For many years strengthening of the compressed reinforced concrete structures was fulfilled by methods based on using reinforced concrete cages and outer metal frames. These are rather time-consuming and expensive processes. The implementation of composite materials in the construction industry made it possible to quicken and simplify the works on strengthening, however with regard to compressed elements it turned to be very resourcedemanding to increase the bearing capacity of rectangular or square section structures. This is primarily due to the limitation in compression strain of the longitudinally located carbon fiber materials and a large decreasing coefficient for transverse composite strengthening. However, the development of new methods of strengthening, including the one considered in this work, will increase the efficiency of composite materials located in the transverse direction by 5–10 times, depending on different variable factors. This article aims to develop and justify a new method of strengthening the reinforced concrete columns by using mixed concrete-composite reinforcement.Materials and methods. This research relies on the results of theoretical calculations. The standard variant of strengthening a compressed reinforced concrete element has been considered and calculated as well as composite materials volume has been specified. Based on the standard calculation results the proposals, which take into account the effect of a new strengthening method, have been made in this article, the detailed methodology of calculation thereof has also been presented. The results of theoretical strength calculations along with comparison of the required volume of reinforcement materials are the key issues in the analysis and drawing conclusions.Results. The research has resulted in development, calculation and justification of the new method of strengthening, which allows reducing the volume of composite materials required for strengthening the compressed reinforced concrete columns.Discussion and conclusion. Three variants of calculating the strengthening of a reinforced concrete column with composite materials have been presented and reviewed in this work. One of which is a standard one, the other two are proposed by the authors. The developed method of strengthening implies rounding of concrete followed by jacketing with composite materials. These roundings can be considered in calculation or can be referred to as structural elements. In any case, the strengthening effect received from the proposed method becomes 5.3 and 10.5 times higher. Besides, further research ideas for continuing the development and study of the method of strengthening the centrally compressed reinforced concrete columns with composite materials are given in conclusion.

Effect of Complex Strengthening on the Continuous Cooling Transformation Behavior of High-Strength Rebar.

The effects of niobium and composite strengthening on the phase transformation characteristics and precipitation behavior of continuous cooling transformation of high-strength rebar during thermal deformation and subsequent cooling were investigated. The results show that when the cooling rate was within 0.3-5 °C/s, ferrite transformation and pearlite transformation occurred in the experimental steels. The Nb content increased to 0.062 wt.%, and the starting temperature of the ferrite transformation decreased. Meanwhile, the ferrite phase transformation zone gradually expanded, and the pearlite phase transformation zone gradually narrowed with the increase in the cooling rate. When the cooling rate was 1 °C/s, bainite transformation began to occur, and the amount of transformation increased with the increase in the cooling rate. It was found that the main precipitates in the experimental steels were (Nb, Ti, V)C, with an average particle size of about 10-50 nm. When the Nb content was increased to 0.062 wt.% and the cooling rate was increased to 5 °C/s, the ferrite grain size was reduced from 19.5 to 7.5 μm, and the particle size of the precipitate (Nb, Ti, V)C could be effectively reduced. The strength of the steel was significantly improved, but the elongation of the steel was reduced. However, the comprehensive mechanical properties of 0.062 wt.% Nb experimental steel was significantly improved at a cooling rate of 5 °C/s.

Numerical investigation of the mechanical behavior of segmental tunnel linings reinforced by a steel plate – Concrete composite structure

Shield tunnels may experience performance degradation caused by uncertainties of the construction conditions and long-term service. Various strengthening methods have been applied to tunnel structures, among which steel plate – concrete composite (SPCC) strengthening is a newly developed approach. It can be applied to strengthen deformed tunnel structures. In this way, a multilayer structure of higher strength and stiffness is obtained. Such strengthened tunnels, however, exhibit a complex mechanical behavior. It is the consequence of the multilayer structure and the existence of joints. A numerical investigation is conducted to study the mechanical behavior of continuous-joint shield tunnels, strengthened by the SPCC strengthening technique. A model with three layers of materials, i.e., a reinforced concrete layer, a layer of self-compact concrete, and a steel plate, is the basis for the analysis of the failure mechanism and the bond forces between different material layers of a strengthened tunnel lining. A parametric study is carried out to investigate the key factors of influence of the structural performance. It is shown that inside the bonds the radial tensile forces reach a maximum at the joints. The tangential shear forces attain a maximum at the joints, with a change of their sign. The results also reveal that the bond strength is the key factor to guarantee the structural strength and ductility. Furthermore, the strength of the steel plates and the degree of damage have a significant influence on the strengthened structure, whereas the strength of the new concrete and the thickness of the concrete layer concerned have a minor influence on the load-bearing performance of the structure. To sum up, this paper contains the presentation of a nonlinear model of a SPCC-strengthened tunnel structure with both reasonable effectiveness and reasonable accuracy. It is validated by experimental tests and refined models. The presented model also provides an effective approach for the analysis of a multilayer composite structure with two interfaces. Furthermore, results from the parametric analysis provide useful suggestions for engineering practice, helping to optimize the strengthening design of existing tunnel structures.

Fatigue behaviour of notched steel beams strengthened by a self-prestressing SMA/CFRP composite

Integrating a NiTiNb-based shape memory alloy (SMA) and carbon fibre-reinforced polymer (CFRP) sheet can achieve a self-stressing SMA/CFRP composite, providing an alternative active (or prestressing) strengthening technology for steel elements. In this study, the effects of retrofitting methods and fatigue load amplitudes on the fatigue behaviour of notched steel beams were experimentally investigated. The retrofitting methods included SMA patch bonding, CFRP sheet bonding, and SMA/CFRP composite bonding. Test results showed that, compared with strengthening methods of CFRP sheets or SMA patches, SMA/CFRP composite strengthening can greatly increase the fatigue lives and slow down the fatigue crack growth rate of steel beam web cracks and interfacial debonding. Besides, the strengthening effect of the SMA/CFRP composite becomes increasingly significant on notched steel beams as the fatigue load amplitude decreases. Additionally, the fatigue life of the SMA/CFRP composite repaired beams was greater than that of the sum of the fatigue life of repaired beams with SMA or CFRP alone. Moreover, SMA/CFRP composite strengthening can effectively reduce the stiffness degradation rate compared with the other two strengthening methods.

Effect of Laser Quenching-Shock Peening Strengthening on the Microstructure and Mechanical Properties of Cr12MoV Steel.

The automobile covering parts mold is a key piece of equipment in the automobile industry, and its drawbead is the core element that affects the life of the mold and the quality of the parts made. Due to the complex structure of the mold cavity for covering parts, there exist differences between material flow characteristics, load conditions, stress strain, failure forms and so on in the surface of different parts of its drawbead and the different directions of the same part of the drawbead, thus putting forward new requirements for material strengthening. For the differentiated lose efficacy forms of the dangerous end faces of the tension bars, this study carried out research into the effect of laser quenching–shock peening strengthening (LQ-LSP) on the organization, plastic deformation resistance and wear resistance of Cr12MoV steel. It was shown that the microhardness (722.30 HV) and residual stress (−383.84 MPa) of the specimens were further enhanced after laser quenching–shock peening composite strengthening. The residual austenite content of the specimen was reduced to 0.8%, and the eutectic carbide distribution morphology was improved. After three rounds of laser composite peening, the specimens had the smallest displacement of the nanoindentation load–depth curve, which exhibited the greatest nanohardness (20.0 Pa) and modulus of elasticity (565.25 Pa), while reducing the coefficient of friction (0.61) and surface roughness (0.152 Ra). The smooth and flat surface of the specimen with shallow and narrow plow grooves improved the resistance of Cr12MoV steel to plastic deformation and wear.

A micromechanical model for the temperature dependent tensile strength of cross-ply fiber reinforced polymer composites

The tensile properties of cross-ply fiber reinforced polymer (FRP) composites at different temperatures have been an essential issue of concern. This work established a temperature dependent tensile strength (TDTS) micromechanical model for cross-ply FRP composites according to the Force-Heat Equivalence Energy Density (FHEED) principle and failure analysis. The combined effects of temperature, fiber strength and its scatter, especially the evolution of constituent’ properties and residual thermal stress with temperature on the tensile strength are considered in the model. The predicted results of TDTS by the model realize a reasonable agreement with the available experimental results. Moreover, the influencing factors analysis regarding the evolution of tensile strength with temperature were performed. This study contributes a reliable theoretical model for predicting the TDTS of cross-ply FRP composites, and provides useful insights for strength evolution with temperature and composite strengthening.

Mechanical and tribological properties of SiC-GNPs composites prepared by oscillatory pressure sintering

SiC-based ceramics, as structural parts and wear-resistant parts, are required to possess outstanding mechanical properties and wear resistant. Herein, to prepare SiC-based ceramics with desirable properties, the effects of graphene nanoplatlets (GNPs) content on the densification, microstructure, mechanical and tribological properties of SiC-GNPs composites by using an oscillatory pressure sintering (OPS) process were investigated. The addition of GNPs could inhibit the growth of SiC grains, and the resultant mechanisms such as crack bridging, deflection, and GNPs pull-out also promoted the strengthening and toughening of such composites. The flexural strength and fracture toughness of the SiC-1.0 wt% GNPs composites attained the maximum values of 515 MPa (∼27% increase) and 7.11 MPa·m1/2 (∼26% increase), respectively. In addition, the friction behavior of SiC-GNPs composites was analyzed by selecting GCr15 steel ball as friction side under drying friction conditions. Compared with pure SiC ceramics, the friction coefficient and wear rate of SiC-1.0 wt% GNPs ceramics were as low as 0.65 (reduced by ∼25%) and 5.17 × 10−7 mm3·N−1·m−1 (reduced by ∼41%), respectively. This phenomenon can mainly be attributed to the lubricating film formed by GNPs during sliding and excellent mechanical properties.

Anti-collision performance of RC columns strengthened with a composite of FRP grid and UHPC

To improve the anti-collision performance of existing reinforced concrete (RC) columns subjected to vehicle impact loading, this paper proposes a composite strengthening method involving the use of fiber-reinforced plastic (FRP) grid and reinforced ultra-high performance concrete (UHPC). An RC column strengthened with the composite of FRP grid and UHPC and an ordinary RC column were prepared to investigate their anti-collision performance under impact loading. Using the methods of numerical analysis and tests, the effects of the vehicle impact velocity, reinforcement layer thickness, and material strength on the anti-collision performance were discussed. The test results showed that the lateral displacement of the RC column significantly decreased after strengthening with the composite. This indicated that the anti-collision performance of RC columns strengthened with the composite of FRP grid and UHPC can be effectively improved. The numerical results showed that the lateral displacement of the strengthened columns was increased by 37.8 % with an increase in the impact velocity from 3.69 m/s to 4.3 m/s; however, the impact velocity had no evident effect on the impact force acting on the surface of the RC columns. In addition, the anti-collision properties of the strengthened RC columns were significantly enhanced with the increase in the FRP grid–UHPC composite thickness and material strength. The lateral displacement of the strengthened RC columns reduced by 7.5 %–13.5 %, and its peak impact force increased by 14.9 %–33.2 % with an increase in the composite thickness from 20 mm to 40 mm. Moreover, the lateral displacement of the strengthened RC columns reduced by 14.5 %–36.1 %, and its peak impact force increased by 10.9 %–46.4 % with the increase in the compressive strength of concrete from 45 MPa to 210 MPa.

Nano-silver modified carbon nanotubes to reinforce the copper matrix composites and their mechanical properties

• The powder electrodeposition technology is employed to synthesize coating material. • CNT-Ag is uniformly distributed in copper matrix. • Ag improves the wettability of carbon nanotubes with copper matrix. • Ag particles played a “pinning” role of the CNTs and improve the load transfer capacity. In ensuring the effective load transfer of carbon nanotubes (CNTs) reinforced copper (Cu)-based composites, good and stable interface contact is a key factor. Powder electrodeposition technology is used in the present study to coat silver (Ag) nanoparticles on CNTs for the first time. Subsequently, by ball milling and spark plasma sintering, uniform distribution of CNTs in the Cu matrix and tight Cu/C interface bonding are successfully achieved. It is found that Ag nanoparticles with a size of 5 nm are evenly embedded in the surface of CNTs. The results reveal that the agglomeration of CNTs is prevented by the addition of Ag nanoparticles and the adhesion between CNTs and Cu matrix is enhanced by the formation of coherent interface. Further, the load transfer of composite materials is effectively realized by the pinning effect of Ag particles on CNTs. The tensile strength, elongation, and conductivity of the 0.75 CNT-Ag/Cu samples were 314 MPa, 24.8%, and 93.6% IACS, respectively, which are 40.1%, 818%, and 3.3% higher than those of the CNT/Cu samples, respectively. The present method provides a new direction for the uniform coating powder materials and the synergistic strengthening of metal matrix composites.

Investigation on steel fiber strengthening of waste brick aggregate cementitious composites

The waste red brick aggregate substituted with natural coarse aggregate can effectively alleviate environmental pollution in engineering concrete constructions. However, its mechanical performance lags far behind natural coarse aggregate due to micro-pore voids and micro-cracks. Three types of steel fiber contents (0, 1%, and 2%) are selected to improve the mechanical behavior of recycled concrete in this study. Cubic compression test, splitting tensile test, prism compression test, and static compressive elastic modulus test are carried out to study the influence of steel fiber content and replacement rate of recycled coarse aggregate. In addition, the stress-strain behavior and failure mechanism of steel fiber recycled brick aggregate concrete are discussed, and microscopic crack development is also analyzed. Test results show that the specimens without steel fiber are prone to aggregate destruction under loading. The cubic and prismatic compressive strength decreased by 48% and 34%, while the splitting tensile strength reduced by 40%. The mechanical properties substantially improve when the steel fiber content is 1%. The finite element model of steel fiber recycled brick aggregate concrete under uniaxial compression is established. The constitutive model for predicting uniaxial compression of steel fiber recycled brick aggregate concrete is also proposed.

Durability of Polyurethane Matrix in Composite Strengthening for Masonry

Earthquakes are highly dangerous for all masonry structures, as they force high deformations that brittle building materials cannot withstand. The solution to such problems may be the use of flexible polyurethane-based technologies (composite strengthening, adhesives etc.). On the other hand, these technologies are relatively new and demand experimental prove, whether they would not lose their properties after being subjected to environmental conditions i.e. temperature fluctuations, humidity, chemically aggressive mortars, solar radiation etc. Herein, we discuss the aspect of durability of Sika PS polyurethane – the polymer used as both composite matrix and an adhesive in flexible protective technologies for masonry.

Study on the strengthening and toughening design of the interlayer interface of GO-based bionic nacre composites and its optimization mechanisms

Inspired by the mineral bridge between hard phase layers of natural nacre, this paper investigates the mechanical properties and optimization strategies of GO-based bionic “brick-mortar” structural composites with interface modification by CNTs. After selectively combining CNTs with GO sheets of different sizes, four biomimetic composites with the same structure but different distributions of strong, medium and weak interfaces were obtained. A comparative study on the mechanical property tests and the finite element simulation results of the samples revealed that the difference in the distributions of different strength interfaces within the material/structure have a significant impact on their localized interfacial failures and subsequent crack extensions, making the deflection of cracks more inclined along the weak interface. Further analysis showed that the targeted and focused optimization of dangerous interfaces with low interfacial bond strength and high stress levels within the material is an effective way to improve the mechanical properties of bionic “brick-mortar” structural composites. The results of the above study will provide useful guidance for the interface optimization and lightweight strengthening and toughness design of composites.

Effectiveness of Concrete Reinforcement with Recycled Tyre Steel Fibres.

The role of searching for industrial waste management solutions in construction is key for environmental protection. Research in recent years has focused on solutions aimed at reducing the carbon footprint. This paper presents the results of tests conducted on concrete reinforced with treated recycled tyre steel fibres (RTSFs) compared to the same amount of manufactured steel fibres (MSFs). The effectiveness of concrete reinforcement with RTSFs was analysed using the fracture mechanics parameters of cementitious composites. Rheological tests, residual flexural tensile strength tests, work of fracture measurements, toughness indices, examinations of the fibre distribution in the concrete, and SEM observations of the concrete fractures with fibres were performed. Determining the work of fracture and toughness indices was an innovative aspect of this paper. As the amount of RTSFs increased, a decrease in the consistency was observed, although the distribution of fibres in the concrete was uniform, as proven by the results of computer tomography tests. Concrete reinforced with RTSFs that is purified and refined during the recycling process might have better properties than concrete reinforced with the same amount of MSFs. The application of RTSFs in construction has environmental and economic benefits in addition to the strengthening of cementitious composites.

Atomistic aspects of load transfer and fracture in CNT-reinforced aluminium

This paper describes atomistic simulations of deformation and fracture of Al reinforced with carbon nanotubes (CNTs). We use density functional theory (DFT) to understand the energetics of Al-graphene interfaces and gain reference data for the parameterization of Al-C empirical potentials. We then investigate the load transfer between CNTs and Al and its effect on composite strengthening. To this end, we perform uniaxial tensile simulations of an Al crystal reinforced by CNTs of various volume fractions. We also study the interaction of the embedded CNTs with a crack. We show that the interaction between CNTs and Al is weak such that, under tensile loading, CNTs can easily slide inside the Al matrix and get pulled out from the cracked surface. This effect is almost independent of CNT length and volume fraction. Little load transfer and consequently no crack bridging are observed during the simulation of pristine CNTs threading the crack surfaces. CNTs that are geometrically fixated inside Al, on the other hand, can increase the fracture stress and enhance plastic dissipation in the matrix. CNTs located in front of a growing crack pin the crack and induce plastic deformation of the Al matrix. Depending on the CNT orientation, these processes can either increase or decrease the failure stress of the composite.

Experimental Investigation of Axial Compression in Composite Strengthened Historical Timber Columns

ABSTRACT This work explores the effectiveness of composite strengthening for historical timber columns, which strengthens the timber columns with near surface mounted steel bars and wrapped CFRP strips. Different numbers of steel bars and two approaches for attaching CFRP strips were compared in tests of 36 timber columns. The failure modes, ultimate load, and ductility of specimens were analyzed. The stress-strain curves and deformation compatibility of each component of specimens were discussed. The results indicate that the composite strengthening effectively enhances the ductility and bearing capacity of strengthened timber columns. Pre-tensioned CFRP strips performed better than the epoxy-bonded CFRP strips in improving the bearing capacity and compression elastic modulus, but not in enhancing deformation performance. Analysis of the strain comparison curves showed that the embedded steel bars and timber can work together in deformation, and that the wrapped CFRP strips can restrain timber columns’ lateral expansion. Overall, reliable and effective strengthening was achieved using the proposed reinforcement method. Finally, according to fitting analysis and related theories about CFRP confined concrete columns, a calculation model of peak loads for strengthened timber columns was established. The reliability of the newly proposed model was verified through the comparison between theoretical and experimental values.

Enhancing strength and electrical conductivity of Cu–Cr composite wire by two-stage rotary swaging and aging treatments

The wide application of Cu–Cr composites is greatly limited by their trade-off of tensile strength and electrical conductivity . In this work, we employed an industrial method of rotary swaging (RS) and subsequent aging to improve the combination of strength and electrical conductivity of Cu-3.11Cr composite wire and reveal the microstructural evolutions during the processes. It is found that the matrix grains of Cu-3.11Cr have been significantly refined and elongated during the deformation and a fibrous structure has been formed. The average diameter of the grains has been reduced to about 3.9 μm after RS processing for an equivalent strain ∼3.5. Moreover, most of the initial micron sized Cr particles are elongated severely along axial direction which plays a role of fiber composite strengthening and reduces the scattering effect of electrons. Besides, lots of nano sized Cr particles re-precipitated in the matrix during the subsequent aging process. After the two-stage swaging and aging, the Cu-3.11Cr composite wire obtained a good comprehensive property with an ultimate tensile strength of 580 MPa and the electrical conductivity of 81.1% IACS (international annealed copper standard). We rationalized the high strength is attributed to dislocation, grain refinement, dispersion and precipitation as well as fiber-composite strengthening. The precipitation of Cr atoms from the Cu matrix during the aging treatment is vital for the enhancement of the electrical conductivity without loss of strength. These findings can provide some new insights in the mass production of the high performance Cu–Cr composites. • Cu–Cr composite wire with enhanced strength and electrical conductivity was prepared. • Two-stage rotary swaging and aging treatments was proposed. • High strength comes from dislocation, grain refinement, dispersion and precipitation.

Microstructure and creep properties of cast near-eutectic Al–Ce–Ni alloys

This study investigates the as-cast and aged microstructures, thermal stability, ambient temperature strengthening, and creep resistance of three ternary Al–Ce–Ni alloys (wt%): near-eutectic Al–10Ce–5Ni (with both eutectic and hypoeutectic regions), hypoeutectic Al-7.5Ce-3.75Ni (with numerous primary Al dendrites), and hypereutectic Al-12.5Ce-6.25Ni (with coarse, blocky primary Al3Ni and Al11Ce3 precipitates and some primary Al dendrites). Depending on the alloy composition and local solidification conditions, the following eutectic morphologies are found: (i) coarse Al–Ce eutectic colonies where Al11Ce3 is in the form of “Chinese script”, (ii) intermingled regions of binary Al–Ce and Al–Ni eutectic colonies, with finer Al3Ni and Al11Ce3 fibers, (iii) large ternary eutectic colonies, where the binary Al3Ni and Al11Ce3 phases are alternating or intertwining within the individual, fine fibers (diameters of ∼60–170 nm, depending on solidification rates), and (iv) ternary eutectic zones (between primary Al dendrites), where fine Al3Ni and Al11Ce3 build up a 3D-interconnected network. The high volume fraction of intermetallic phases and extremely fine eutectic spacing/fiber diameter both contribute to high ambient strengthening (higher as-cast microhardness than binary Al–Ce or Al–Ni), and also provide enhanced creep resistance at 300 and 350 °C. The alloys are coarsening-resistant up to 425 °C for extended periods, with a gradual decrease in microhardness. The alloys aged at 400 °C to 1050 h show fiber fragmentation and coarsening of the resulting particles, with the faster-diffusing Ni driving more rapid coarsening of the Al3Ni particles which engulf finer, more stable Al11Ce3 particles. Severe overaging (performed at 590 °C for 24 h) leads to Al3Ni and Al11Ce3 spheroids which remain submicron-sized in eutectic colonies, but micron-sized at colony boundary and at Al dendrite-eutectic interface. Creep resistance at 300 °C of overaged Al–10Ce–5Ni remains substantial, consistent with load-transfer based composite strengthening being an important strengthening mechanism in these alloys, making them excellent candidates for replacement of heavier steel or titanium parts operating under stress up to 300 °C.

Microstructure and properties of layered metal/rubber composites subjected to cyclic and impact loading

The paper is devoted to investigation of microstructure and mechanical properties of five-layered metal/rubber composites. The composites were produced by hot bonding of alternating low carbon steel or/and aluminum alloy and rubber layers. Metal/rubber composites can be used as vibration and sound absorbing material in constructions of high-speed trains. In order to study mechanical properties of five-layered metal/rubber composites, impact cyclic and fatigue tests of the obtained composites with different structure was carried out. The tear test results indicated that adhesion bond strength of steel/rubber joint is higher than one of aluminium/rubber joint for the reason of activating and passivating effect of oxide films at interfaces. The impact test results shown that layered architecture of the composite with steel (60 vol%) and rubber (40 vol%) component provides holding of composite‘s impact strength at the level of monolithic low carbon steel with reducing the weight of steel products on 30%. The increased resistance of metal-rubber composites to fatigue fracture at ambient temperature under 100,000-cyclic bending was established. Grain-subgrain refinement, increase in dislocation density and fragmentation of large inclusions were realized on the outer steel and aluminium layers of composites under cyclic loading. The microstructure transformation led to strengthening of composites.

Laser powder bed fusion of Mo2C/Ti-6Al-4V composites with alternately laminated α′/β phases for enhanced mechanical properties

Mo2C/Ti64 composites with nearly full densification and enhanced tensile strength were developed by using laser powder bed fusion (LPBF). The addition of 1–3 wt% Mo2C particles with an average particle size of ~ 1 µm enabled the LPBF-printed composites with an alternately laminated α′-Ti/β-Ti microstructure along with Mo2C and in-situ synthesized M23C6 (M was Ti, Al, V, and Mo). During LPBF, most of the Mo2C particles were incorporated into the Ti64 matrix, resulting in the α′-Ti and β-Ti solid solutions. The segregation of Mo contributed to the generation of the β-Ti phase at the melt pool boundaries of the composites, leading to the alternating hard α′-Ti/soft β-Ti phases. Remarkable improvements of 22.8% and 19.5% in the hardness and tensile strength of the Ti64 matrix were achieved, respectively. The strengthening of the LPBF-printed composites was associated with the formation of the laminated α′-Ti/β-Ti structure, solid solution behavior of Mo and C, and presence of the remaining Mo2C and precipitated M23C6. The findings are anticipated to provide insights into the selection of reinforcement materials for additively manufactured composites with nearly full densities and greater mechanical strength.