Manufacturing processes of aircraft, automobile and electronic components involve a lot of stretch-forming of sheet metals. The processes contain a large amount of straining which, in turn, may lead to plastic instabilities such as necking, slip formation or shear banding. Understanding the instability phenomenon requires the development of constitutive description of material characterizing the plastic instability and post uniform deformation behavior. The previous work on plastic instability usually lacks the experimental verification of the theoretical models. This may be owing to the complexity involved in designing a suitable experimental methodology for accurate measurements of strain in the locally deforming zone as the deformation progresses rather rapidly once the local neck sets in. A review of the important methodologies and analyses that were and are used in investigating instability of sheet metal in uniaxial tension is presented in this paper. Some supporting results are also presented.
Low-density polyethylene (LDPE)-coated sisal fiber prepreg was prepared by using solution coating process. These coated fiber prepregs were consolidated to make composites having different weight fraction of sisal fibers in a hot compression-molding machine. This experimental study reveals that higher loading of sisal fiber up to 57wt% in LDPE-sisal composites is possible by this technique. Mechanical and abrasive wear characteristics of these composites were determined. The tensile strength of composites increased with the increase in sisal fiber concentration. Coating thickness of LDPE was varied by changing the viscosity of LDPE-xylene solution that manifested to different weight fraction of fiber in sisal-LDPE composites. Mechanical, dynamic mechanical, and abrasive wear characteristics of these composites were determined. The tensile strength and modulus of sisal composites reached to 17.4 and 265 MPa, respectively, as compared to 7.1 and 33MPa of LDPE. Storage modulus of sisal composites LD57 reached to 2.7 3 10 9 MPa at 408C as compared to 8.1 3 10 8 MPa of LDPE. Abrasive wear properties of LDPE and its composites were determined under multi-pass mode; pure LDPE showed minimum specific wear rate. The specific wear rate of composites decreased with the sliding distance. Increase of coated sisal fiber content increased the specific wear rate at all the sliding distances, which has been explained on the basis of worn surface microstructures observed by using SEM. POLYM. COM-POS., 34:650-655, 2013. ª FIG. 2. Variation of storage modulus (E 0 ) and loss modulus (E 00 ) against temperature. FIG. 3. Plot for specific wear rate versus sliding distance for different samples under multi-pass mode.
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