Mechanics of Composite, Hybrid and Multifunctional Materials, Volume 5

In this chapter, the microstructural formation and static/cyclic compression behavior of recycled Alumix (aluminum alloy) matrix hybrid composites reinforced with TiB₂, TiC, and B₄C are studied. It is aimed as an alternative to traditional alloys/composites used in the aeronautical industry. These composites are generally produced by using a combined sintering + forging process. The static and dynamic properties are evaluated in detail, taking into account the relevant scanning electron microscopy microstructures (including the distribution of reinforced elements).

Within the framework of the common research project, the mechanical properties and fatigue behaviour of recycled thin sheet Ti-Al-based composites reinforced with atomized scrap aluminium (AA7075) and Nb elements have been evaluated. All the thin sheet sandwich structures were produced by the hot forging process, which is a semi-solid-forming process similar to partial melting hot forging. The effect of the chemical bonds during the production of these multifunctional sandwich composite structures was analysed using 3-point bending tests under static and dynamic (fatigue) loading conditions. Additional tensile tests have been carried out to evaluate the mating effect. Interface and microstructure of these composites have also been evaluated using scanning electron microscopy.

Among the various renewable energy sources, wind energy offers an effective solution to energy providers. Onshore wind turbines are generally designed for sites with low wind resources, while offshore wind turbines can be more efficient in producing energy, thanks to their longer blades that provide more than 10 MW of rated power. Offshore wind turbine blades are subjected to significantly higher stresses and harsh environmental conditions. Therefore, self-healing composites can offer cost-effective and long-lasting solutions for wind turbine blade manufacturers since self-healing is a prominent mechanism used in various industrial applications to repair the structures in the presence of a crack. In this study, the advantage of using self-healing mechanism in laminate composites is studied. Following manufacturing of self-healing microcapsules, they are incorporated into laminate composites by means of vacuum-assisted resin transfer molding (VARTM) method. Then, mechanical characterizations and microscopic examinations are carried out through tensile and Charpy impact tests. In this study, it is intended to examine the mechanical influence of using the self-healing microcapsules, as well as the curing scenario is analyzed in detail by comparing the test results. It is seen that the self-healing agent ratio of 2.5% has the optimum ratio when we compare it with 5% and 7.5% healing agent ratio. In addition to that, curing temperature of 100 °C increases the UTS when it is compared with 80 °C.

A new recycled hybrid composite has been designed by using a special doping process and a combined method, “sintering + forging” of recycled “AA 7075 + AA1050” and basically used rice husk as a fine powder and graphene nanoplatelets. Static and cyclic behaviours of these composites and also time-dependent behaviour called modified fatigue behaviours have been evaluated under compression solicitation. A detailed damage analysis has been performed using scanning electron microscopy.

In this study, the microstructural formation and static/cyclic compression behavior of “Ni-Al+AA7075+AA1050”-based composites reinforced with ceramics (TiC-TiB₂) have been evaluated. It is aimed at creating a new design to be an alternative to traditional alloys/composites used in the aeronautical industry. These composites are generally produced using a combined method that we call “sinter + forging processes”. The static and dynamic properties and also the microstructure (including the distribution of reinforcement elements) are evaluated in detail.

In this research, the mechanical properties of recycled aluminum (A356-A7075)-based composites reinforced with Nb₂Al-ZrO₂-TiAl have been evaluated. Different amounts of Nb₂Al doped with ZrO₂ were mixed with atomized recycled aluminum matrix containing “AA356-A7075” and processed by ball milling. The mixture was then sintered followed by hot forging. Static and cyclic stress relaxation compression tests and low velocity impact tests were carried out to evaluate damage behavior. Interface and microstructure of these composites were also evaluated by scanning electron microscope (SEM).

Nowadays, additive manufacturing technologies allow coupling peculiar material properties with complex shapes to obtain cellular materials capable of exhibiting advanced multi-functionalities. Among them, self-sensing materials are increasingly valuable for applications where structural integrity monitoring is needed without external measurement instruments. This study exploits the piezoresistive properties of composite materials coupled with their own 3D-printed shapes. Therefore, understanding and modelling piezoresistive behaviour is getting a need. The piezoresistive behaviour of 3D printed composite material has been investigated under quasi-static and dynamic compression loadings. An innovative split Hopkinson bar set-up is introduced in order to measure the change in electrical resistance of composite material during the high strain rate compression. The strain rate and temperature effects on the material’s piezoresistivity behaviour are discussed. Based on experimental evidence, a strain rate-dependent parameter is introduced into piezoresistivity analytical theory. The analytical findings are compared with the experimental ones.

The use of carbon fiber-reinforced polyetheretherketone (PEEK) produced through additive manufacturing is crucial due to its exceptional physical and mechanical characteristics, such as its high strength, stiffness, temperature resistance, chemical resistance, lightweight, and biocompatibility. This makes carbon fiber-reinforced PEEK a valuable material in various industries like aerospace, automotive, medical, and electronics. This study investigates the effect of short carbon fibers on the mode-I fracture behavior of PEEK composites made through additive manufacturing. The research employed Fused Filament Fabrication (FFF) to create both short carbon fiber-reinforced and non-reinforced PEEK as the baseline. A compact tension fracture test was conducted to measure the mode-I fracture toughness, and elastic-plastic fracture theory was used to calculate the inter-layer and cross-layer crack growth resistance. Unreinforced PEEK samples showed stable crack growth with significant plastic energy dissipation, whereas short fiber reinforcement resulted in unstable crack growth with subtle plastic energy dissipation. For the examined fiber volume fraction and utilized FFF parameters, the carbon fiber caused a significant decrease in the mode-I fracture toughness of 3D-printed PEEK. The inclusion of fiber reinforcement led to a reduction of approximately 50% in elastic fracture energy and about 80% in total fracture energy. This observation can be attributed to the high fiber volume percentage.

Vitrimers are a new class of polymeric materials, which contain exchangeable cross-links. In the recent years, several polymeric reactions and chemical modifications are introduced in the synthesis of vitrimers. Among them, the vitrimers based on thermoplastic materials are of high interest because they exhibit high flowability when heated, while retaining the cross-linked structure at higher temperature. This aids in the preparation of highly rigid vitrimers at relative ease. In this study, vitrimers based on thermoplastic polymeric material poly(butylene terephthalate) are synthesized. Particulate-reinforced composites are prepared from the vitrimers by introducing hollow glass beads (HGB) at different weight percentages. The mechanical behaviour of these innovative materials is studied using Digital Image Correlation (DIC) technique. The experimental campaign shows the potential of these innovative composites in the structural applications.

The deformation and fracture behaviors of polymer-particle composites with high solids loading (≥80% wt.) are dependent on the pressure-dependent viscoelasticity of the polymer, the fracture strength of the particle, and the bonding strength at the polymer-particle interfaces. By performing dynamic compression experiments at intermediate strain rates (<2000 1/s), deformation regimes dominated by characteristics of the polymer, particle, or their interfaces are explored. Composite polymer-particle samples are fabricated by curing polydimethylsiloxane and either silica sand or sodium chloride in a mold at elevated temperature and pressure. To characterize the as-fabricated samples, we present data of particle strength through quasistatic, uniaxial, confined compression experiments and data of the composite stress-strain behavior through quasistatic and uniaxial compression experiments. A new split Hopkinson pressure bar facility has been installed at the Turbomachinery Laboratory Center at Texas A&M University and is used to compress these polymer-particle composites at intermediate strain rates. Preliminary testing across a range of intermediate strain rates provides an initial assessment of bulk deformation and fracture behavior.

This study summarizes a previously developed approach for modeling high-velocity impact on multilayered plain weave composites. This approach is evolved here to include a stochastic mesostructure, which more realistically models a real plain weave composite. The mesoscale modeling approach resolves plain weave architecture with mesoscale detail and applies the continuum assumption to the microscale. Previously developed models include rate-dependent material constitutive, damage and failure behavior, and rate-dependent cohesive interfacial failure. Rate-dependent cohesive traction-separation laws were derived from previously published microscale models of fracture. The modeling approach was validated by comparing the predicted impact versus residual velocity (VI-VR) response to previously published experimental results. In this work, the modified model is used to predict the VI-VR response for a 22-layer composite, and the results are compared with experimental results from the literature. Good correlation is shown between experiment and model predictions.