Weifeng Jiang

Study of the knife stab and puncture-resistant performance for shear thickening fluid enhanced fabric

This work developed a shear thickening fluid enhanced fabrics and the influence of the shear thickening fluid types on the knife stab and puncture resistance performance were investigated. The rheological properties of the shear thickening fluids were tunable by varying both the dispersing particles (silica, polymethylmethacrylate and polystyrene-ethylacrylate) and the mediums (ethylene glycol, polyethylene glycol 200 and polyethylene glycol 600). The mechanical properties of the shear thickening fluid reinforced fabrics were evaluated by the knife and spike drop tower testing, respectively. The hardness of the particles was the dominant factor for the knife stab resistance, while the inter-yarn friction played as the critical role for improving the puncture resistance. In comparison to neat fabric, the knife stab and puncture resistance of the shear thickening fluid-fabrics exhibited significant enhancement, which can be proven by the results of yarn pull-out testing and optical microscope images investigation. The enhancing effect was systematically discussed and the improving mechanism was analyzed. Because the influencing factors for the knife stab resistance and puncture resistance were different, the enhancing effect of the dispersing particles and the mediums for the shear thickening fluid-fabrics should be also different.

Stress pulse attenuation in shear thickening fluid

The stress pulse attenuation of the 62 vol/vol. % dense silica particle-ethylene glycol suspension was investigated by using a modified spilt Hopkinson pressure bar. In comparison to the neat ethylene glycol solution, the transmission pulse of the shear thickening is much weaker under the same impact condition. No energy loss is progressed for the neat ethylene glycol solution, thus it can be concluded that the energy dissipation behavior was happened in the silica particle based shear thickening fluid. In this work, the energy dissipation of the shear thickening fluid was reversible.

Multifunctional polymer composite with excellent shear stiffening performance and magnetorheological effect

A novel multi-functional polymer composite (MPC) with both excellent shear stiffening (ST) performance and magnetorheological (MR) effect is prepared by dispersing magnetic particles into shear stiffening polymer matrix. Besides having the magnetically dependent mechanical properties (MR effects), this multi-functional MPC automatically changes its rheological behavior in response to external shear stimuli. The mechanical properties of this smart composite can be alternatively achieved by varying the particles types and contents. Upon applying a shear stress with excitation frequency from 1 Hz to 100 Hz, the storage modulus (G′) of the MPC increases from 102 to 106 Pa, demonstrating an excellent ST effect. Interestingly, the ST effects of the MPC are also tunable by varying the external magnetic field, and the area of G′ could be greatly increased and precisely controlled. Based on the experimental results, a possible mechanism is proposed and discussed. It is believed that the “cross bonds” and the particle chains induced by the magnetic field are due to the excellent multi-functional stimulus-response properties.

Rate-dependent and self-healing conductive shear stiffening nanocomposite: a novel safe-guarding material with force sensitivity

A novel rate-dependent and self-healing conductive composite with a well-defined shear stiffening (S-ST) effect was facilely fabricated by dispersing multi-walled carbon nanotubes (MWCNTs) into a shear stiffening polymer matrix. The storage modulus (G′) of the multi-functional composite automatically increased 4 orders of magnitude when encountering external shear stimuli and the G′max was over 1 MPa, demonstrating an obvious shear stiffening effect and good safe-guarding performance. It was found that the electrical conductivity changed accordingly when shear stiffening occurred, therefore it can be applied as a force sensor during the attacking process. The rate-dependent piezoresistance effect of the composite was investigated. In quasi-static compression and high rate impact tests, different force signals can be obtained because of the negative and positive piezoresistivity effect. Self-healing tests indicated that the as-prepared composite can maintain its mechanical and electrical properties after destruction and healing treatments. Owing to the shear stiffening performance, the rate dependent conductive composite could both absorb impact energy and sense the attacking forces. Finally, a mechanism was proposed and it was believed that the glass transition induced by B–O interactions and the changes in the microstructure during the external action can be attributed to the S-ST performance and rate dependent electrical conductivity, respectively.

The role of shear in the transition from continuous shear thickening to discontinuous shear thickening

Dense non-Brownian suspension has rich rheology and is hard to understand, especially for distinguishing continuous shear thickening (CST) from discontinuous shear thickening (DST). By studying the shear stress dependent rheology of a well-known DST suspension of cornstarch in water, we find that the transition from CST to DST could occur not only by increasing the volume fraction ϕ but also by increasing the shear stress σ. For the recovery process of jammed suspension, we observe that the shear activates the time-dependent nature of particle rearrangement. DST can then be interpreted as the consequence of shear-induced jamming. Based on the test data, we plot the schematic phase diagram in the ϕ-σ plane and find out that ϕ and σ perform almost the same effect on flow-state transition.

MAGNETORHEOLOGICAL ELASTOMERS BASED ON POLYURETHANE/SI-RUBBER HYBRID

A kind of magnetorheological elastomers based on polyurethane (PU)/silicone rubber (Si-rubber) hybrid is fabricated without applying magnetic fields. The MR effect is improved by optimizing preparation conditions, in particular by adjusting PU/Si-rubber ratio, and improving compatibility between PU and Si-rubber. The influences of the preparation condition and the relationship between the microstructure and MR effect of this kind of magnetorheological elastomers are discussed in detail. The results show that this kind of MR elastomers has better MR effect than that of MR elastomers based on pure Si-rubber or PU matrix with same testing conditions. SEM analysis indicates that the former forms a peculiar interpenetrating microstructure in the presence of PU in the matrix. The maximum increase in shear modulus of this kind of MR elastomers can be up to 0.5MPa when exposed to a magnetic field of about 0.2T.

Strain rate-induced phase transitions in an impact-hardening polymer composite

An impact-hardening polymer composite that is promising as a protective equipment material for its excellent performance and comfortable characteristics is shown. Falling weight impact experiments are performed to characterize its protective behavior, which is realized by absorbing energy and resisting deformation. From the mechanical tests in different strain rate, it is seen to undergo transitions from a viscous-liquid behavior to a rubbery behavior, then to a glassy behavior. These phase transition are found to be essential for their practical applications in the energy absorption and the deformation resistance.