Papers by Keyword: Tearing

Abstract: Aluminum alloys in the 7000 series are high-strength alloys that are used in a wide variety of products in the transportation equipment and aerospace fields to reduce weight. In particular, the A7075 alloy has the highest strength and is expected to find further applications in a wide range of fields such as aircraft parts and sporting goods. However, low productivity is a problem due to its high deformation resistance, tendency to produce surface defects called tearing on the product surface, and short tool life. Tearing tends to occur under high temperature and high speed conditions, and is thought to be caused by local melting of Zn, an additive element, due to heat generation in processing. In this study, to improve the productivity of A7075 alloy, the profile was cooled during extrusion to prevent recrystallization of extrudate surface grains due to processing heat and to prevent processing heat during forming. In order to investigate the cooling effect, hot extrusion simulation was conducted. The cooling effect successfully suppressed the occurrence of tearing. These results indicate that cooling the extrudate during forming reduces the effect of heat generation during forming and prevents recrystallization of the extrudate surface grains and local melting of Zn.

Abstract: 7000 series aluminum alloy is a high-strength alloy and used in a wide variety of products for the purpose of weight reduction in the field of transportation equipment and aerospace. In particularly, A7075 alloy has the highest strength and is expected to be further applied in a wide range of fields such as aircraft parts and sports equipment. However, it has high deformation resistance and is prone to surface defects called tearing. Tearing affects the productivity because it requires to lower the speed. Tearing is likely to occur under high temperature and high speed conditions. It is thought that the localization of melting of Zn-compounds and additive compounds occur due to heat generated during process leading to tearing. In this study, in order to increase the productivity without tearing, die surface quality was considered to prevent the effect of friction and generated heat at interface between tools and material. In addition, recrystallization was also eliminated by reducing friction because temperature does not increase up to the range of recrystallization temperatures. The AlCrN coating was used to improve die surface quality comparing to Nitriding. It was found that the tearing size and heat generated by using AlCrN coating were small. In addition, grain size was small and observed at the tearing region on the extruded surface. It is thought that the die coating can reduce the effect of friction at interface and prevent the recrystallization of the extruded surface. Furthermore, the localization of melting of Zn-compounds and additive compounds are also decreased. From above results, tearing sensitivity can be decreased by using coating to increase productivity speed of A7075 alloy.

Abstract: Warp yarn of cotton samples were printed with pigment dyes has been investigated. The printed warp yarn was weaved by using white cotton yarn as a weft yarn. The physical properties were evaluated to testing in tensile strength and tearing strength of weaved samples, the test were determined according to ISO standard. The results showed that the tensile strength of three samples are shown to be in the range between 210 and 342 Newtons whereas tearing strength was in the range between 30 and 110 Newtons. The results indicated that the properties of printed samples (handling) were good to very good level.

Abstract: The fracture behaviour of laminated materials was studied in this work. The materials used in this work were low-density polyethylene (LDPE) laminated on polyethylene (PET). The thickness of the LDPE was 27 µm and the PET was 100 µm. Experiments were performed by using a 2-leg trousers specimen to analyse the tearing behaviour of the laminate in relation to the delamination. A clear delamination zone was observed during the crack propagation by tearing. Furthermore, a finite element calculation was performed to simulate the behavior around the crack tip during the tearing. A correlation between adhesion and crack propagation was discussed. Finally, the theory of Essential Work of Fracture (EWF) was used for predicting the specific total work of fracture along the tear path across the plastic zones.

Abstract: Both tensile and tear strength values of PLAxEGMCy blown-film specimens in machine and transverse directions improve significantly and reach the maximum values as their EGMC contents approach an optimum value of 6 wt%. The melt shear viscosity values of PLAxEGMCy resins measured at varying shear rates are significantly higher than those of the PLA resin and increase consistently with their EGMC contents. FT-IR analysis suggest that the carboxylic acid groups of PLA molecules react with the epoxy groups of EGMC molecules during the reactive-extrusion processes of PLAxEGMCy specimens. Further DMA and morphological analysis of PLAxEGMCy specimens reveal that EGMC molecules are phase-separated with PLA molecules at EGMC contents equal to or more than 2 wt%, since distinguished phase-separated EGMC droplets and tanδ transitions were found on fracture surfaces and tanδ curves of PLAxEGMCy specimens, respectively. Possible reasons accounting for the above interesting properties of the PLA/EGMC specimens are proposed in this study.

Abstract: The purpose of this study is to find out the AE characteristics and fracture mechanisms through AE signal analysis for the weldment, PWHT specimen and basemetal of the pressure vessel steel. Charpy sized specimens were taken from the multi-passed weld block. Specimens were given to four point bend and AE tests. Lots of AE signals were emitted from the weldment compared with the basemetal and PWHT specimen. Besides, amplitude for the weldment was the largest, followed by PWHT specimen and basemetal and more AE counts for the weldment were emitted in the process of deformation. Lots of microcracks around the notch for the weldment were formed so that more AE signals were produced. In addition, second phase particle such as MgO for the basemetal acts as AE source. However, in case of weldment, debonding mechanisms between matrix and hard oxides which are formed during welding in air attributed to the emission of AE signals and softened particles for the PWHT specimen cause to produce the low level AE signals.