B. Zhu

Theoretical Modeling of Large Shear Deformation and Wrinkling of Plain Woven Composite

In hot stamping operations, the primary deformation mode of plain woven textile composite is shear deformation between yarns. In-plane picture frame test is an effective method to characterize the materials shear behavior. By proposing theoretical models based on our experimental study [19,20], the present article estimates the non-linear stiffness of the textile fabric during large shear deformation and the onset of wrinkling under additional yarn tension/compression at various temperatures. The relevant properties of materials are determined from experiments, and general mathematical expressions are formulated to predict the shear energy and the critical shear angle for textile composite fabrics of similar types. In addition, the size effect of the test sample is also investigated.

Novel fabric pressure sensors: design, fabrication, and characterization

Soft and pliable pressure sensors are essential elements in wearable electronics which have wide applications in modern daily lives. This paper presents a family of fabric pressure sensors made by sandwiching a piece of resistive fabric strain sensing element between two tooth-structured layers of soft elastomers. The pressure sensors are capable of measuring pressure from 0 to 2000?kPa, covering the whole range of human?machine interactions. A?pressure sensitivity of up to 2.98 ? 10 ? 3?kPa ? 1 was obtained. Theoretical modeling was conducted based on an energy method to predict the load?displacement relationship for various sensor configurations. By adjusting the Youngs modulus of the two conversion layers, as well as the geometrical dimensions, the measurement ranges, and sensitivities of the sensors can be quantitatively determined. The sensors are being used for pressure measurements between the human body and garments, shoes, beds, and chairs.

Flexible pressure sensors for smart protective clothing against impact loading

The development of smart protective clothing will facilitate the quick detection of injuries from contact sports, traffic collisions and other accidents. To obtain real-time information like spatial and temporal pressure distributions on the clothing, flexible pressure sensor arrays are required. Based on a resistive fabric strain sensor we demonstrate all flexible, resistive pressure sensors with a large workable pressure range (0?8?MPa), a high sensitivity (1?MPa?1) and an excellent repeatability (lowest non-repeatability ?2.4% from 0.8 to 8?MPa) that can be inexpensively fabricated using fabric strain sensors and biocompatible polydimethylsiloxane (PDMS). The pressure sensitivity is tunable by using elastomers with different elasticities or by the pre-strain control of fabric strain sensors. Finite element simulation further confirms the sensor design. The simple structure, large workable pressure range, high sensitivity, high flexibility, facile fabrication and low cost of these pressure sensors make them promising candidates for smart protective clothing against impact loading.

Soft Fiber Optic Sensors for Precision Measurement of Shear Stress and Pressure

This paper reports a soft fiber optic sensor based on polymer fiber Bragg gratings (PFBGs) for simultaneous measurement of shear and normal stresses. The sensor comprises two PFBGs embedded in soft polydimethylsiloxanes (PDMS) matrix, and one of them is horizontally placed while the other is tilted. The transduction principle is that applied normal and/or shear stresses lead to deformation of the matrix and induce strains on gratings. Finite element simulation reveals non-uniform strain distribution along two fibers for direct imbedding that is verified by theoretical analysis, and therefore four gaskets are used to stretch polymer optical fibers from two ends and to produce strains on gratings. The fabricated sensor is tested by concurrently applying normal and shear forces, and Bragg wavelength shifts of two gratings were found to be linearly dependent on stresses in two directions. The measured pressure sensitivity is 0.8 pm/Pa in the range of 2.4 kPa and the shear stress sensitivity is 1.3 pm/Pa for a full range of 0.6 kPa. Such soft sensors are especially suitable for high precision measurement of contact stresses involving human skins and tissues because they are similar in Youngs modulus to the used PDMS.

Large Shear Deformation of E-glass/ Polypropylene Woven Fabric Composites at Elevated Temperatures

Stamping operation of textile composite sheets in industry involves a process of heating and cooling of the material. In the present article, the in-plane large shear deformation of woven fabric composite sheets at elevated temperatures is studied. Using the modified ‘picture frame’ test, the effects of temperature on the shear behavior of the material and the onset of wrinkling were investigated. In addition to the reduction in yarn width, the change of physical and mechanical properties of polypropylene (PP) fibers with temperature also plays a significant role. The initial shear stiffness of the composite sheets and the onset of wrinkling are reasonably explained by inter-yarn friction measurement. To simply consider the temperature effect, the introduction of a temperature-dependent factor for the simulation of stamping operation is suggested.

Fabrication and evaluation of a notched polymer optical fiber fabric strain sensor and its application in human respiration monitoring

This paper describes an intensity-based notched polymer optical fiber (POF) fabric strain sensor and its application in human respiration monitoring. A mechanical analysis illustrates geometrical profiles of constrained fiber loops on the fabric substrate. V-shaped notches are made by laser ablation on the sides of the POFs. The effects of loop parameters and processing conditions on the sensing performance are investigated. The experimental results show that the fabric sensor is more sensitive to strain with notches on the outer side of the loops, a small radius of the loops and a low scanning speed of laser. This fabric sensor exhibits a large measurable strain range of up to 21%. The achieved strain sensitivity is 3.77. The temperature and relative humidity have little effect on strain sensitivity between 0℃ and 60℃. A belt has been fabricated by integrating the fabric sensor for monitoring human respiration. The evaluation trials show a strong correlation between the belt system and a clinic monitor.

DEFORMATION ANALYSIS AND FAILURE MODELLING OF WOVEN COMPOSITE PREFORM IN GENERAL BIAS EXTENSION

A series of bias extension tests was carried out on balanced plain woven composite preforms with various aspect ratios, disclosing that different aspect ratios may result in different initial failures. An energy method is adopted to quantify several deformation modes. By the competition of the required energies, the initial failure is predicted, showing a good accordance with the experimental observation. The results of the present research are valuable for the further understanding of the material’s behaviour in bias extension test. It also provides an effective way for modelling the material’s formability in other more complicated forming processes.

Large Deformation and Failure Mechanism of Plain Woven Composite in Bias Extension Test

Large shear deformation of plain woven composite sheets and corresponding failure mechanism are investigated by bias extension test. Digital image correlation analysis was conducted on a series of photos taken during the test. Four typical phases were identified, and a theoretical model of the large deformation is proposed from energy point of view. Numerical simulations have also been carried out, but it will be reported in a subsequent paper.