| With the development of textile science and technology,the dual functional characteristics of textile are becoming increasingly obvious.The fabrics which have the both functionality of wearability and strain sensitivity were developed rapidly,and gradually replacing the implantable sensors to become a kind of dual functional fabric with the same texture and shape.The intelligent sensory fabric "artificial skin",which integrates sensing materials,information science,data processing and storage and ergonomics,has become a research hotspot in the field of high-tech textiles.Textiles are typical wearable materials,while electronic products such as sensors are usually rigid.How to make electronic devices flexible and wearable is an urgent problem.One effective solution is by converting traditional fiber,yarn or fabric as the intrinsic sensitive materials and converting the mechanical or strain information into electrical detection signals.In this paper,functional mechanical sensors with resistance and inductance as the detection signals were constructed by using the metal coated filament as the raw material and taking advantage of the special structure of the spring sheathed composite yarn.The sensitive yarn can be used for human motion detection such as joints bending and the health signals monitoring such as human respiration,as well as the three-dimensional human motion and body reshaping.First of all,the composite yarn with silver plated nylon filament sheath and spandex filament core was prepared by self-made wrapping spinning system.The surface morphology and load-electrical behavior of the composite yarns with different twists were characterized and analyzed.A static and dynamic tensile mechanical model for composite yarn which has a good consistency with experimental results was established,and the conductive mechanism of the composite yarn was further discussed.By in-situ observing the static and dynamic surface morphology of spring sheathed composite yarn with different twists,it is found that the wrapping structure of composite yarn was uniform and stable.The theoretical critical contact twist of spring sheath is 472 ~ 649(twist/10cm),which has a good consistency with the experimental results.The mechanical behavior of spring sheathed composite yarn in the strain range of 0%~100% showed a typical nonlinear tensile mechanical behavior,and the yarn twist has a positive correlation with the modulus.From the dynamic mechanical test results of-80℃ ~ 190℃,it can be seen that the dynamic mechanical properties of the composite yarn in the tensile strain amplitude of 10 μm are close to that of the spandex core yarn.The loss rate of the energy storage modulus E’ reached 96% at 0 ℃.The fatigue data under deformation are fitted by using a double logarithm linear model,and the relationship between stress and fatigue life is exponential in 6000 times of cyclic stretching.Three viscoelastic models for the spring sheathed composite yarns were established,and the best fitted three element structure model which can accurately express the nonlinear tensile mechanical behavior of the composite yarn is selected.By analyzing the composition and influence factors of the conductive channel of the composite yarn,the contact state of the wrapped yarn with different twist and its contribution to the conductive performance of the composite wire are clarified.The resistance model for the composite yarn with different twist is also proposed.Secondly,the strain-resistance variation mechanism for spring sheathed composite yarn with different twists is theoretically analyzed.The sensitivity,linearity,response time and stability of the composite yarn based sensor as well as the influence of structural parameters on the performance were characterized and analyzed.It can be found that the separation of the helix critical contact point,the unfolding of the stacked fibers and the fiber elongation are the three main factors which affect the resistance change of the yarn sensor.The yarn sensor with a twist of 450 ~ 900(twist / 10cm)has an obvious electrical response in the strain range of 0% ~ 100%.The sensitivity of the yarn sensor reaches the maximum value of 64 at 726 twist / 10 cm,and the linear fitting correlation of the composite yarn sensor is higher than 0.99 in the range of 1% ~ 5% strain.A best linearity can be found in the twist of 450 twists / 10 cm with a nonlinearity of only 0.11%.The electrical signal response of the resistance sensor based on the spring sheathed composite yarn is relatively stable when it is stretched for 800 times,which illustrated that the silver coating on the nylon surface was stable and would not suffer obvious damage during the stretching process.Unlike the mechanical fatigue property,the electrical property of the composite yarn has no obvious attenuation,which shows that the resistance change of the composite yarn during the cyclic test mainly results from the strain variation.In addition,by taking advantage of the spring sheathed composite structure,a kind of yarn inductance is prepared by using the spandex elastic yarn as core yarn and polyester coated copper yarn as sheath.By measuring the mechanical and electrical behavior of the composite yarn,the effectiveness and reliability of the composite yarn based self-inductance and mutual-inductance sensors were verified.The stress-strain relationship of the inductive yarn was theoretically analyzed with the viscoelastic mechanical behavior models.According to the electrical signal change in the stretching process,the characteristic curve of strain-inductance change rate is obtained.It is found that the sensor sensitivity was enhanced with the core number increasing.In the strain range of 0% ~ 40% and 60% ~ 100%,the linear fitting correlation was greater than 0.99,indicating a good linearity in these two stages.Moreover,the inductive yarn sensor has a timely and stable inductance signal output.Furthermore,the wireless passive detection of the yarn tensile strain is realized by utilizing the mutual inductance effect between the composite yarn inductance and the adjacent inductance.When the inductive yarn passes through the reading coil,mutual inductance is generated at the resonance frequency of 191 MHz.The tensile strain induced inductance decrease resulted in the resonance frequency increasing,and the resonance frequency shifts to the right.The sensitivity of the resonance frequency of the composite inductor is 0.28 MHz/kPa.With the help of the inductive coupling between the reading coil and the reading coil,the non-contact and wireless passive detection of the tensile displacement and the tensile force is realized through the test of the resonance frequency.By combining the spring sheathed composite yarn sensor with the garment,the human actions such as human joint movements and the health signals such as human breath were real-time monitored.What’s more,the three-dimensional human bodies model for virtual fitting system were established.The sensors can also be used for finger gesture recognition,elbow and wrist joint bending and recovery motion monitoring.When the volunteers wear the tight clothing sewn with the yarn sensor on the upper abdomen,the respiratory frequencies of the volunteers were consistent with the results measured by the traditional respiratory function monitoring instrument,which showed that the yarn sensor could be used to detect the muscle contraction fluctuation caused by the abdominal breathing of the human body;For three-dimensional human body reshaping,combining with the corresponding relationship function between electrical signal and human body movement or body shape signal,the human body gesture can be simulated by the measured electrical signal.The reshaped human body model had a good consistency with the actual results.In this paper,the strain-deformation mechanism,mechanical behavior and conductive mechanism of the spring sheathed composite yarn are systematically analyzed,and the strain-electrical behavior and sensing mechanism of the strain sensor are explored.It has certain scientific value in the discussion of the spring sheath composite wire structure forming,mechanism analysis and intelligent wearing application.These results provided theoretical guidance for intelligent textile which can be used for human motion and health monitoring and human body reshaping. |
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