This work aimed to investigate progressive collapse behaviors and mechanisms of the 3D printed thin-walled composite structures under quasi-static compression and dynamic impact conditions. The thin-walled structures were manufactured by fused deposition modeling technique, using polyamide and fiber-reinforced polyamide-based composite. Four kinds of configurations (circular, triangular, quadrangular and hexagonal cross-sections) were studied. The experimental tests were carried out by a universal material testing machine for quasi-static compression (10 mm/min) and a drop hammer testing system for low-velocity impact (10 m/s). It was found that thin-walled composite structures presented progressive stable and regular plastic deformation mode under quasi-static compression. Under low-velocity impact condition, the thin-walled structures presented the progressive brittle crack-to-fractured collapse mode. The collapse mechanisms analysis revealed that plastic deformation mode consisted of bending deformation and membrane deformation. The fractured mode involved micro fiber breakage, fiber–matrix debonding and matrix cracks. With increasing the loading velocity, peak crushing force increased, while specific energy absorption decreased. The hexagonal structures made by carbon-fiber-reinforced material presented the best energy absorption performance under both quasi-static compression and dynamic impact conditions. • Half-wavelength of progressive collapse mode under quasi-static compression was investigated. • The progressive collapse mode showed ductile-to-brittle transition with increasing the loading velocity. • The strain rate effect increased the mechanical properties but decreased the energy absorption performance. • The collapse mechanisms for structures under quasi-static compression and dynamic impact conditions were studied. • The hexagonal carbon-fiber-reinforced structure presented the highest energy absorption under multi-conditional loading. 

Progressive collapse behaviors and mechanisms of 3D printed thin-walled composite structures under multi-conditional loading

A class of bionic gradient thickness (BGT) tubes with 2 cross-sectional shapes (circle and rectangle) are proposed. The energy absorption and deformation modes of four thin-walled tubes, including a bionic circular tube (BCT), and a bionic rectangle tube (BRT) with gradient thickness, and the counterpart uniform-thickness (UT) tubes, namely circular tube (CT) and rectangle tube (RT), are analyzed by Ls-Dyna. Before detailed analysis, the simulation and bionic design are verified by quasi-static experiments, which show that the BCT has better deformation than the CT, and the experimental curves also are well consistent with the simulation. The BCT has a better energy absorption capacity when subjected to different oblique loading angles. The selection and parameterization of sample points are studied based on full-factor tests. The design factors significantly affect the specific energy absorption (SEA) and peak force (PF) of the BCT under multi-angle oblique loading. Finally, the multi-objective optimization design considering the load angle is conducted to obtain the optimal design of the BCT. The optimum BCT has a 9.3% higher SEA compared with CT. Moreover, there is a mass reduction of 4% than the CT.

Experiment and numerical simulation study on the bionic tubes with gradient thickness under oblique loading

Crashworthiness analysis of gradient hierarchical multicellular columns evolved from the spatial folding

A new type of axially varying thickness lateral corrugated tube (AVTLCT) is proposed. The crashworthiness of the AVTLCT under axial impact has been systematically studied. The studies show that the initial peak crushing force (PCF) increases as the amplitude increases and axial variation coefficient (k) decreases. The starting positions of all folds of the AVTLCT with axial variation coefficient k>0 are near the impact end. As the number of corrugations increases, the number of folds decreases and the fluctuation of the AVTLCT increases during the impact. Compared with the AVTLCT with k = 0 , the AVTLCT with k>0 has absolute advantages in the two key crashworthiness indicators, PCF and crush force efficiency (CFE). PCF is reduced by up to 44.53%, and CFE is increased by up to 81.72%. Finally, a surrogate model of the AVTLCT is constructed using the radial basis function approximation, and the interactive effects of structural parameters on crashworthiness indicators are analyzed. The nondominated sorting genetic algorithm II is used to perform multiobjective optimization under unconstrained and constrained conditions.

Energy absorption characteristics of axially varying thickness lateral corrugated tubes under axial impact loading

Quasi-static and low-velocity impact behavior of the bio-inspired hybrid Al/GFRP sandwich tube with hierarchical core: Experimental and numerical investigation

A review of the crashworthiness performance of energy absorbing composite structure within the context of materials, manufacturing and maintenance for sustainability

Nanofluids are promising heat transfer fluids, which possess superior heat transfer properties compared with those of conventional fluids such as water, ethylene glycol, and engine oil. Nanofluids ...

Thermal and electrical conductivity of silicon carbide nanofluids

This study was designed to experimentally measure the thermal and electrical conductivities of Aluminium Nitride/Ethylene Glycol (AlN/EG) nanofluids. Transmission electron microscopy (TEM) was used to characterize the shape of AlN nanoparticles. Nanoﬂuids with different particle volume concentrations of 0.5%, 1%, 2%, 3%, 4%, and 5% were utilized. The thermal and electrical conductivities of the nanofluids were measured using a KD2-Pro thermal analyser and electrical conductivity meter, respectively. The obtained results revealed that the thermal conductivity of the nanofluids increased at the higher volume concentration of the nanoparticles. Thus, at 5% volume concentration, the maximum thermal conductivity enhancement of 25% was obtained. The addition of AlN nanoparticles to the EG base fluid resulted in a significant increase in the electrical conductivity of the nanofluid. An enhancement in the electrical conductivity of approximately 520 times relative to the base fluid was attained by loading a 0.5% volume concentration of AlN in EG at 28°C.

http://www.ijnd.ir/article_668325_e320ca0ae3dbaaf4e8273d77d6d109fd.pdf

Thermal and electrical conductivity of Aluminium Nitride nanofluids

The quest for effective and efficient heat exchange systems has been a subject of recent research. Nanofluids are high performance ultra-modern heat transfer fluids with superior properties compare...

Experimental investigation on viscosity of AlN and SiC nanofluids

ABSTRACT
 The quest to have an effective and efficient heat transfer fluids has been a subject of great research interest for several decades. Nanofluids are preeminent fluids that have garnered increased attention recently due to their enhanced thermal properties. Moreover, viscosity is an essential characteristic of nanofluids and for this reason, many research works have been conducted on this subject over the last few decades. In this work, attempt is made to present the viscosity model of nanofluids. In addition, efforts are put forth to examine the existing empirical, semiempirical, and analytical correlations utilized for the evaluation of viscosity of nanofluids. Furthermore, there are a number of factors influencing the viscosity of nanofluids which has necessitated this review work. These factors not only feature the nanoparticle concentration, sizes, and types, they also include the temperature of the nanofluid as well as the base fluid surfactant and stability. This review also discuss several industrial applications of nanofluids such as those used for electronic cooling, solar applications, heat exchangers, and automotive industry. The available experimental results show that the above mentioned parameters have considerable effect over viscosity of nanofluid. However, there is no general trend to describe the influence of particle sizes on increase in viscosity. The lowest enhancement in viscosity with increase in nanoparticle concentration in literature was graphite/engine oil nanofluid with improvement of 6.25% with volume concentration increasing from 1 to 5.5%. It has also been observed that many empirical models have been formulated on viscosity of nanofluid; however, there is no universally accepted model. This review leads to some directions for future research in nanofluids.

Chidozie Ezekwem

Papers

A review of the crashworthiness performance of energy absorbing composite structure within the context of materials, manufacturing and maintenance for sustainability

Thermal and electrical conductivity of silicon carbide nanofluids

Thermal and electrical conductivity of Aluminium Nitride nanofluids

Experimental investigation on viscosity of AlN and SiC nanofluids

A Recent Review of Viscosity Models for Nanofluids