Anna Boczkowska

Microstructure-property relationships of urethane magnetorheological elastomers

Studies on the structure of urethane magnetorheological elastomers (MREs), with respect to their magnetic and mechanical properties, are reported. MREs were obtained from a mixture of polyurethane gel and carbonyl-iron particles cured in a magnetic field of 100 and 300 mT. Samples with different numbers of particles (1.5, 11.5 and 33 vol%) were produced. The microstructure and magnetic properties of the obtained MREs were studied. Also, the displacement of the samples in an external magnetic field was examined using a specially designed experimental set-up. The influences of the number of ferromagnetic particles and their arrangement in relation to the external magnetic field were investigated. It was found that the microstructure of the MREs depends on the number of ferrous particles and the fabrication conditions. The orientation of the iron particles into aligned chains is possible for a lower volume content of the ferromagnetic fillers. The high carbonyl-iron volume content in the matrix leads to the formation of more complex microstructures, similar to three-dimensional lattices. The magnetic measurements also confirmed the existence of the microstructure anisotropy for the MREs with 1.5 and 11.5 vol% of iron particles. The structural and magnetic anisotropy has not been found in the MREs with 33 vol% of Fe. To evaluate the effect of the external magnetic field on the magnetorheological properties, the displacement under magnetic field, the compressive strength, and the rheological properties were measured. The experiments showed that both the particle content and the field strength used during curing have a significant effect on the microstructure of the MREs and, in consequence, on their properties.

The effect of carbon nanotubes on epoxy matrix nanocomposites

The paper concerns thermal properties of epoxy/nanotubes composites for aircraft application. In this work, influence of carbon nanotubes on thermal stability, thermal conductivity, and crosslinking density of epoxy matrix was determined. Three kinds of nanotubes were used: non-modified with 1- and 1.5-μm length, and 1-μm length modified with amino groups. Scanning electron microscopy observations were done for examining dispersion of nanotubes in the epoxy matrix. Glass transition temperature (Tg) was readout from differential scanning calorimetry. From dynamic mechanical analysis, crosslinking density was calculated for epoxy and its composites. Also, thermogravimetric analysis was done to determine influence of nanotubes addition on thermal stability and decomposition process of composites. Activation energy was calculated from TGA curves by Flynn–Wall–Ozawa method. Thermal diffusivity was also measured. SEM images proved the uniform dispersion of carbon nanotubes without any agglomerates. It was found that nanotubes modified with amino groups lead to the increase of epoxy matrix crosslinking density. The significant increase in Tg was also observed. On the other hand, addition of carbon nanotubes leads to the decrease of thermal stability of polymer due to the increase of thermal diffusivity.

Microstructure and Properties of Magnetorheological Elastomers

Magnetorheological elastomers (MREs) belong to the new group of the functional materials called “smart”. Although smart materials are known since long time, their intensive development started in the end of the XXth century. The term smart materials, intelligent materials or less frequently used adaptive materials or multifunctional materials, was introduced in the eighties of the twentieth century, when some materials, which were included in the group were already known. Till today there is no accepted universal definition of smart material, it is also not included in the encyclopedia devoted to these materials, published in 2002 [1, 2].

Analysis of Vibration Measurements in a Composite Material Using an Embedded PM-PCF Polarimetric Sensor and an FBG Sensor

Low frequency vibration measurements in composite materials using embedded optical fiber sensors are presented in this paper. The two types of fiber sensors embedded are a polarization maintaining photonic crystal fiber (PM-PCF) polarimetric fiber sensor and a fiber Bragg grating (FBG) sensor. A glass fibre reinforced polymer composite material sample is fabricated with both fiber optic sensors embedded in it. A comparison between the performance of both the PM-PCF polarimetric fiber sensor and the FBG sensor embedded in the composite material is also presented.

Tuning Active Magnetorheological Elastomers for Damping Applications

Magnetorheological elastomers (MREs) were obtained by mixing soft polyurethane and carbonyl-iron particles. The effect of the volume fraction of the ferromagnetic particles on the MREs microstructure and properties, as well as their arrangement in relation to the external magnetic field were investigated. As a ferromagnetic component carbonyl–iron powder, with particle size from 6-9µm, was used. The amount of the carbonyl iron particles was varied from 1.5 to 33.0 %(v/v). The samples were produced with randomly dispersed and aligned carbonyl iron particles. Scanning electron and light microscopy techniques were used for the MRE microstructure observations. The rheological properties (G’, G’’ and tan δ) of the MRE were tested without and with the application of the magnetic field. It was found that the microstructure of MREs, particularly the amount and arrangement of the carbonyl-iron particles, has a significant influence on their rheological and damping properties.

Urethane Magnetorheological Elastomers - Manufacturing, Microstructure and Properties

In this paper studies on urethane magnetorheological elastomers (MREs) microstructure in respect to their magnetic and mechanical properties are reported. MREs were obtained from a mixture of polyurethane gel and carbonyl-iron particles cured in a magnetic field of 100 and 300 mT. The amount of particles was varied from 1.5 to 33 vol. %. Samples with different arrangements of particles were produced. Effect of the amount of ferromagnetic particles and their arrangement on microstructure and properties in relation to the external magnetic field was investigated. The microstructure was studied using scanning electron microscopy. Magnetic properties were measured using vibrating sample magnetometer. Rheological and mechanical properties under compression were also examined.

Effect of the processing conditions on the microstructure of urethane magnetorheological elastomers

The aim of the study was to develop an innovative processing method of magnetorheological elastomers (MRE). This method comprises optimization of the MRE structure in the context of their performance in the magnetic field. The influence of the amount of ferromagnetic particles and their arrangement in relation to the external magnetic field was investigated. As matrixes various elastomers, with different stiffness, were used. Their properties were compared with commercially available silicone rubbers. It was found that the structure of the MRE produced depends on the viscosity of the matrix before curing and the magnetic field strength applied. Two different magnetic field strengths were used: 100 and 300 mT. The amount of the carbonyl iron particles was equal to 1.5, 11.5 and 33.0 vol. %. Scanning electron and light microscopy techniques were used for the MRE microstructure observations. The influence of curing conditions on the thermal properties of the MRE was investigated. To evaluate the external magnetic field effect on the magnetorheological properties a deflection under magnetic field was measured. The experiment showed that application of the magnetic field increases stiffness of the material.

Novel MRE/CFRP sandwich structures for adaptive vibration control

The aim of this work was the development of sandwich structures formed by embedding magnetorheological elastomers (MRE) between constrained layers of carbon fibre–reinforced plastic (CFRP) laminates. The MREs were obtained by mechanical stirring of a reactive mixture of substrates with carbonyl-iron particles, followed by orienting the particles into chains under an external magnetic field. Samples with particle volume fractions of 11.5% and 33% were examined. The CFRP/MRE sandwich structures were obtained by compressing MREs samples between two CFRP laminates composed. The used A.S.SET resin was in powder form and the curing process was carried out during pressing with MRE. The microstructure of the manufactured sandwich beams was inspected using SEM. Moreover, the rheological and damping properties of the examined materials with and without a magnetic field were experimentally investigated. In addition, the free vibration responses of the adaptive three-layered MR beams were studied at different fixed magnetic field levels. The free vibration tests revealed that an applied non-homogeneous magnetic field causes a shift in natural frequency values and a reduction in the vibration amplitudes of the CFRP/MRE adaptive beams. The reduction in vibration amplitude was attributed mainly to the stiffening effect of the MRE core and only a minor contribution was made by the enhanced damping capacity, which was evidenced by the variation in damping ratio values.

The influence of thermal expansion of a composite material on embedded polarimetric sensors

Some of the most critical issues of the influence of the thermal expansion of composite materials on embedded polarimetric sensors for measurements of strain and temperature are studied in this paper. A composite material sample with polarimetric fiber sensors embedded in two distinct layers of a multi-layer composite structure is fabricated and characterized. The polarimetric fiber sensors used in this study are based on Panda type fiber and polarization maintaining photonic crystal fiber (PM-PCF). The temperature sensitivities of polarimetric fiber sensors with acrylate buffer coated and buffer stripped polarization maintaining optical fibers are measured in free space and compared with those for sensors embedded in the composite material. It is found that a polarimetric fiber sensor with an acrylate coating embedded in the composite material shows the same response as the one in free space while the coating stripped fiber polarimetric sensor shows significant temperature sensitivity when embedded in the composite material. This is due to the stress induced change in birefringence created by the thermal expansion of the composite material, while in the case of a buffer coated fiber, the effect is considerably reduced as the thermal stress is largely eliminated by the buffer coating. The results obtained in this study demonstrated that thermal expansion of the composite material is the main source of error in strain and temperature measurement using embedded polarimetric fiber sensors and that more accurate strain and temperature measurements can be obtained with buffer coated polarimetric fiber sensors.

Polyurethanes from crystalline prepolymers

Abstract Cast, segmented urea–urethane polymers, obtained from crystalline urethane prepolymers in a reaction with water, were studied. Hitherto the reaction with water was conducted exclusively with liquid prepolymers. If the polycondensation reaction with water is carried out with the prepolymer solidified as a result of its crystallization, rather than the liquid prepolymer, in the cast products the formation of discontinuities in the polymer bulk as carbon-dioxide gaseous phase is eliminated or significantly suppressed. A similar method of cast polyurethane preparation is not known from available literature. Terathane 2000 oligomer was used for prepolymer preparation. The prepolymer was crystallized at various temperatures, and subsequently chain-extended with water. The crystalline polymers thus produced were examined prior to, and after samples were heated to transform the soft-segment crystalline phase into an amorphous state. The effect of prepolymer crystallization temperature and of the chain-extension conditions on the structure of the polymers obtained was investigated. Relations between certain structural features and mechanical properties of the polymers studied were learned. The polymer structure, hence soft-segment crystalline phase content and the degree of phase separation were found to be affected by the prepolymer crystallization point. An analogous effect of crystallization point on the Terathane 2000 oligomer and its prepolymer structures was observed. The effect of prepolymer crystallization point on the crystallizability of hard segments was also revealed.