Pullout test fabrics

Pullout test is also a method, providing useful information about fabric tearing, its ability to absorb energy especially in ballistic applications, lllnishing efCbiency, bending, and shearing hysteresis of the fabric and Qially the frictional behavior of the fabric. 

In yam pullout test a rectangular fabric sample (for simplicity a plain pattern is considered here) is clamped to the two opposite side of a U frame. The pullout force is applied to a single yam (for instance at the middle) with a specific free end length as shown in Figure 1. The yam is pulled out in three steps, the detail of which will be given in the discussion part of the chapter. 

FIGURE 1 Schematic of fabric deformation in yam pullout test. 

The pullout test repeated Qve times for each fabric. In the execution of the yam pullout test, a fabrie sample was clamped to each side of a U form frame. The weft yams of the fabric were free. The frame was connected to the movable lower head of a Zwick tensiometer model 1440-60 . The middle weft yam was tied to the stationary upper head while a free length at the end was set to be 1 cm. The length of the yams between the upper head and the fabric was set to be 6 cm for all samples. The lower head moved down at a velocity of 10 mm/min. The pullout force was measured by a load cell with a maximum capacity of 500 N while the pulled yam fully pulled out of the weave. 

Figure 8 illustrates a comparison between experimental proQes of the pullout test and the theoretical model. The diagrams are related to one selected sample of each fabric. 

In this study the yam pullout test is applied to investigate internal mechanical properties of the plain woven fabrics. In the first step an analytical model was developed, inputs of which employs simple mechanical properties such as the fabric modtrlus, the weave angle, and the fabric deformation angles during the pullout test. This model predicts important mechanical parameters such as the weave angle variations, the yam-to-yam friction coefficient, the normal load in crossovers, the lateral forces, and the opposed yam strain within the fabric. This approach may be extended to other types of the woven fabrics. 

In the next step, the experimental analysis was employed to evalirate the vahdity of the predicted parameters of the force balance model. Here the force displacemerrt pro Qe of the yam pullout test was simulated using the equations of the force balance model, and the characteristics of the plain woven fabric and its yams. 

As a physical study, yam pullout test would be an appropriate approach to realize an estimation of the internal friction forces between the yams within the fabric. Under the circumstances of this test, a pulled yam sUdes along the intersecting perpendicular yams during fabric deformation. 

By three last decades, several models have been presented to simulate the behavior of woven fabrics in a yam pullout test. The advantage of this test is the simulation of internal frictional interactions. Concerning to the principals of the method [38] de-... 

Variation of crimp angle for the opposed yam due to fabric deformation by angle a during pullout test (Figure la) 0 = arctan(tan0 cos a) (7)... 

Five plain woven fabrics, two polyester fabrics, and three cotton fabrics were examined in a yam pullout test, as schematically shown in (Figure 1(a)). Characteristics of these fabrics are presented in (Table 2). Sample PETl is consisted of twisted multi filaments of polyester as weft and warp yams. Sample PET2 has intermingled polyester multi filaments as warp and textured polyester multi filaments as weft yams. The COTl is a scoured cotton fabric with ringspun yams as wefts and warps. The COT2 is a bleached cotton fabric with ringspun weft and warp yams, and finally COTS is a bleached cotton fabric with open-end spun wefts and warps. 

The sample is clamped in a relaxed condition along the warp directiom Therefore, the warp yams are the opposed yams. The middle weft yam with a 10 mm free end was pulled in the pullout test. The pulling velocity was 10 nun/min and it kept Deed until the pulled yam left the weave completely. The pullout force was measured by a Zwick tensiometer model 1440-60 (made in Germany). The test was repeated Q e times for each fabric. 

By measuring 6, in warp direction, yam linear density, and fabric deformation angle in pullout test, /tg, and of oscillation model can be computed using Equa-... 

Valizadeh, M., Hosseini Ravandi, S. A., Salimi, M., and Sheikhzadeh, M. Determination of internal mechanical characteristics of woven fabrics based on the force balance analysis of yam pullout test. Journal of Textile Institute, 99, 3755 (2008). 

Force balance model is capable of predicting the irttemal mechanical parameters of the plain woven fabrics in a similar yam prrllout test based on the force distribution concepts. These parameters are yam-to-yam friction coef ftierrt, normal load at crossovers, lateral forces, lateral strairr, weave angle variatiorrs, arrd pullout force. Crimp angle of yams within the fabric 9 in (Figure 3)), its elastic modulus and linear density and fabric deformation data (a in (Figure 1(a))) are the required empirical factors of force balance model. The main equations of this model are presented in (Table 1) [10] ... 

Carbon fiber/Si3N4 composites were fabricated using slip infiltration of fiber bundles, subsequently stacked in a plaster mold, dried, glass encapsulated and HfPed to form unidirectional composite test bars. Neither chemical reactions between fiber and matrix, nor thermal mismatch cracks in the matrix were observed. The bend fracture behavior of the composites was non-brittle with extensive fiber pullout. 

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