On The Fabric Roughness From The Surface Texture Composition

Roughness sensation of fabrics is the human feeling of smooth or rough when skin contacts fabric surfaces. It is a comprehensive physical and psychological reaction caused by the surface morphology and texture features that act on the skin and tactile organs of human body. The roughness sensation of fabrics is one of the primary tactile texture perceptions. It influences the style of fabrics and wear comfort. The evaluation of fabric roughness includes physical, physiological, psychological as well as many other factors.In previous studies, the evaluation of fabric roughness adopted sensory evaluation or statistical inference between subjective and objective tests. However, there is not a consensus on the relationship between roughness sensation and mechanical and physical properties. There are following two reasons. On one hand, sensory evaluation lacks of means of quantitative description. For example, the KES system tests only the geometrical roughness and friction properties of fabric surface to predict roughness. On the other hand, previous studies could not identify the basic stimulus responsible for the generation of roughness sensation. As results, the types of statistical relations varied with the objective testing methods and sensory evaluation results. From the results of psychophysical experiments from such object as grating and sand paper, cognitive scientists have discovered that roughness sensation is not only correlated with the average height of object surface textures, but also the textures spacing and harmonic wave components of surface profiles. By analyzing the rough surface consisting of Sine or square waves, it is found that the perceived short wavelength roughness magnitude is decided by the basic components of wave curve's FFT amplitude, and the long wavelength roughness sensitivity depends on the greatest magnitude of harmonic components. Therefore, it is not enough for analyzing fabric roughness from the average height of surface textures, but needs considering the textures spacing and harmonic wave characteristics.Considering the harmonic components of surface morphology contributed to different roughness sensations and based on the curve of fabric surface texture by KES surface morphology test, the present study includes:(1) Calculate the average roughness of fabric samples, as well as the inter-peak distance of different levels of amplitude, obtain harmonic wave components by a FFT analysis, and then compare the correlations between the average geometrical roughness, inter-peak distance and height of surface textures with roughness sensation. From the morphology curve (height and inter-peak distance) and harmonic amplitude to characterize roughness sensation of fabric, the study explores the basic physical stimulation formation of roughness sensation. The results indicate that fabric roughness sensation is related to both the average geometrical roughness and the inter-peak distance of surface textures. Also, the correlation between roughness sensation and maximum amplitude of harmonic wave is significantly higher than that with the morphology curve.(2) The nature that skin mechanoreceptors sense the roughness of fabric surfaces is to convert the mechanical stimulation energy acting on the cell surface receptors to electrochemical energy. In viewing of this, the present study explores the relationship between the fabric surface fluctuation curve and roughness sensation by a power spectrum analysis method. Combined with sensory evaluation tests, the study analyzes the effects of harmonic wave power on roughness sensation. A new approach is made to measure fabric roughness by means of the power spectral density. Comparing with the average roughness by KES it is shown that the inter-peak distance of surface textures, maximum amplitude and power of harmonic wave have a better correlation with sensory evaluation. It also shows that the average roughness cannot accurately reflect the fabric roughness. The results indicate that roughness sensation of fabric is closely related to the fluctuation power of surface morphology curve, and that the intensity of roughness sensation depends mainly on the maximum power of harmonic wave components. The study of roughness sensation in the perspective of the amplitude and energy component of harmonic waves can not only reflect the characteristics of fabric texture, but also conforms with the physiological mechanism of human tactile perception.From the studies on the relationship between surface texture characteristics of fabric samples and roughness sensation, the following conclusions are obtained:(1) The difference of fabric roughness sensation depends on the inter-peak distance of surface textures and the maximum amplitude of harmonic wave components. The structure of harmonic is the basic stimulus contributing to the difference of surface roughness sensation.(2) When fabric surface roughness are perceived by the touch manner, it shows that the higher the maximum power of harmonic wave is, the rougher the hand of the fabric surface is. The correlation between roughness sensation and the maximum power (or the maximum amplitude component) of harmonic wave is higher than that between roughness sensation and the average geometrical roughness.