Numerical analysis of plastic deformation of a circular sheet metal subjected to transverse impact loading

Based on the concept of Tensor Code a numerical method is presented for analysis of the plastic deformation process of circular sheet metals subjected to transverse impact loading. In the solution process, the equation of motion is solved explicitly with finite difference method in a series of small time steps over a Lagrangian mesh of zones. Using this method, a code has been developed and utilized for investigation of the deformation behavior of an explosively loaded circular sheet metal under various conditions. Deformation characteristics of a sheet under rectangular and triangular pressure distributions are discussed. It is shown that when these simple distributions are combined with each other, their individual effects on the deformation behavior are also combined in the deformation process. Effects of shape and duration of pressure pulse as well as boundary conditions have been explored. Moreover, results of the numerical simulation have been compared with those of theoretical solution and experiments reported by other researchers. Good agreements between them show the validity of the developed code.     

Numerical and Experimental Investigation of Temperature Effect on Thickness Distribution in Warm Hydroforming of Aluminum Tubes

Reduction of weight and increase of corrosion resistance are among the advantageous applications of aluminum alloys in automotive industry. Producing complicated components with several parts as a uniform part not only increases their strength but also decreases the production sequences and costs. However, achieving this purpose requires sufficient formability of the material. Tube hydroforming is an alternative process to produce complex products. In this process, the higher the material formability the more uniform will be the thickness distribution. In this research, tube hydroforming of aluminum alloy (AA1050) at various temperatures has been investigated numerically to study temperature effect on thickness distribution of final product. Also a warm hydroforming set-up has been designed and manufactured to evaluate numerical results. According to numerical and experimental results in the case of free bulging, unlike the constrained bulging, increase of the process temperature causes more uniform thickness distribution and therefore increases the material formability.     

Copolymerization of ethylene/α‐olefins using bis(2‐phenylindenyl)zirconium dichloride metallocene catalyst: structural study of comonomer distribution

Catalysts have a major role in the polymerization of olefins and exert their influence in three ways: (1) polymerization behaviour, including polymerization activity and kinetics; (2) polymer particle morphology, including bulk density, particle size, particle size distribution and particle shape; and (3) polymer microstructure, including molecular weight regulation, chemical composition distribution and short‐ and long‐chain branching. By tailoring the catalyst structure, such as the creation of a bridge or introducing a substituent on the ligand, metallocene catalysts can play a major role in the achievement of desirable properties. Kinetic profiles of the metallocene catalyst used in this study showed decay‐type behaviour for copolymerization of ethylene/α‐olefins. It was observed that increasing the comonomer ratio in the feedstock affected physical properties such as reducing the melting temperature, crystallinity, density and molecular weight of the copolymers. It was also observed that the heterogeneity of the chemical composition distribution and the physical properties were enhanced as the comonomer molecular weight was increased. In particular, 2‐phenyl substitution on the indenyl ring reduced somewhat the melting point of the copolymers. In addition, the copolymer produced using bis(2‐phenylindenyl)zirconium dichloride (bis(2‐PhInd)ZrCl₂) catalyst exhibited a narrower distribution of lamellae (0.3–0.9 nm) than the polymer produced using bisindenylzirconium dichloride catalyst (0.5–3.6 nm). The results obtained indicate that the bis(2‐PhInd)ZrCl₂ catalyst showed a good comonomer incorporation ability. The heterogeneity of the chemical composition distribution and the physical properties were influenced by the type of comonomer and type of substituent in the catalyst. Copyright © 2010 Society of Chemical Industry     

Investigation of the high velocity impact behavior of nanocomposites

In this article, the ballistic behavior of the glass/epoxy/nanoclay hybrid nanocomposites is studied. The fiber glass used is a plain weave 200 g/m², while the nanoclay is an organically modified montmorillonite nanoclay (Closite 30B). The epoxy resin system is made of Epon 828 as the epoxy prepolymer and Jeffamine D‐400 as the curing agent. 0, 3, 5, 7, and 10 wt% of nanoclay particles are dispersed in the epoxy resin. Ballistic tests are performed using flat‐ended projectiles in impact velocities 134 m/s and 169 m/s. The results show that the energy absorption capability and mechanical properties of the composite can be significantly enhanced by adding nanoparticles. When the impact velocity is 134 m/s, near than the ballistic limit, the most increase in the energy absorption capability is observed in 3 wt% nanoclay while with the impact velocity 169 m/s, beyond the ballistic limit, the highest increase is observed in 10 wt% nanoclay. POLYM. COMPOS., 37:1173–1179, 2016. © 2014 Society of Plastics Engineers     

Inspection error and its effects on single sampling plans with fuzzy parameters

In this paper we have designed an acceptance single sampling plan with inspection errors when the fraction of defective items is a fuzzy number. We have shown that the operating characteristics curve of this plan is like a band having high and low bounds, its width depends on the ambiguity of proportion parameter in the lot when the samples size and acceptance numbers are fixed. A comparison of the single sampling plans with and without inspection errors was done to study the effects upon the characteristics. The results of this comparison show that in the sampling plan with inspection errors, there is a lower operating characteristics band in comparison to a sampling plan without inspection errors for good processing quality. We have also shown that the incorrect classification of a good item reduces the fuzzy probability of acceptance and incorrect classification of a defective item results in a higher fuzzy probability of acceptance.     

A comment on the axial crush of metallic honeycombs by Wu and Jiang

In the paper published by Wu and Jiang (Int. J. Impact. Eng. 19(5/6) (1997) 439), the experimental results of quasi-static and impact tests on six types of honeycomb cellular structures have been compared with theoretical predictions. The values of some of the parameters used in the formulae in their paper, seem to be incorrect. In this paper the cause of inaccuracy and the correct values of these parameters have been presented.     

Polyurethane-SAPO-34 mixed matrix membrane for CO2/CH4 and CO2/N2 separation

SAPO-34 nanocrystals (inorganic filler) were incorporated in polyurethane membranes and the permeation properties of CO₂, CH_4, and N₂ gases were explored. In this regard, the synthesized PU-SAPO-34 mixed matrix membranes (MMMs) were characterized via SEM, AFM, TGA, XRD and FTIR analyses. Gas permeation properties of PU-SAPO-34 MMMs with SAPO-34 contents of 5 wt%, 10 wt% and 20 wt% were investigated. The permeation results revealed that the presence of 20 wt% SAPO-34 resulted in 4.45%, 18.24% and 40.2% reductions in permeability of CO_2, CH_4, and N₂, respectively, as compared to the permeability of neat polyurethane membrane. Also, the findings showed that at the pressure of 1.2 MPa, the incorporation of 20 wt% SAPO-34 into the polyurethane membranes enhanced the selectivity of CO₂/CH₄ and CO₂/N₂, 14.43 and 37.46%, respectively. In this research, PU containing 20 wt% SAPO-34 showed the best separation performance. For the first time, polynomial regression (PR) as a simple yet accurate tool yielded a mathematical equation for the prediction of permeabilities with high accuracy (R² > 99%).     

Forming Limit Diagram Prediction of Tailor-Welded Blank Using Experimental and Numerical Methods

The forming limit diagram (FLD) is a useful method for characterizing the formability of sheet metals. In this article, different numerical models were used to investigate the FLD of tailor-welded blank (TWB). TWBs were CO₂ laser-welded samples of interstitial-free (IF) steel sheets with difference in thickness. The results of the numerical models were compared with the experimental FLD as well as with the empirical model proposed by the North American Deep Drawing Research Group. The emphasis of this investigation is to determine the performance of these different approaches in predicting the FLD. These numerical models for FLD are: second derivative of thinning (SDT), effective strain rate (ESR), major strain rate (MSR), thickness strain rate (TSR), and thickness gradient (TG). Results of this research show necking will be happened, when the value of MSR, TSR, ESR criteria is maximum, TG????0.78 and SDT criterion has the first peak in forming process time. The value of dome height of TWB samples at failure was predicted based on the numerical models for samples with different widths. These numerical predictions were compared with the experimental results. The SDT model indicates a better agreement with experimental results in prediction of both the FLD and the limit dome height (LDH) in comparison to the other numerical models. Both numerical and experimental results show that minimum of LDH is happened in plane strain condition.     

Modeling Transient Evaporation from Descending Shallow Groundwater Table Based on Brooks–Corey Retention Function

In arid and semi-arid regions a large amount of rainfall and irrigation water that enters into the soil is lost through soil surface via evaporation. In such regions, there are some areas with shallow groundwater table, evaporating huge amounts of water and accumulating salts at the soil surface. Thus, the evaporation phenomenon not only is responsible for water loss but also is a major reason for soil salinization. The objective of this study was to develop and verify an analytical model for one dimensional transient unsaturated upward flow from water table to soil surface. Consequently, an analytical solution was developed based on the Richards equation with initial and boundary conditions governing evaporation phenomenon. The parametric Brooks and Corey retention function was used to describe water status in the vadose zone. Based on the proposed model, the saccumulative evaporation is estimated as function of water table drawdown and soil retention parameters. To collect the data required for model verification, nine large lysimeters were constructed and packed with sandy loam, silty clay loam, and silty clay soil textures. The results indicated reasonable agreements between the experimental data and those predicted with the proposed model. Although the overall predicted results were well resemble the real conditions, there were some underestimations for a certain period. This can be attributed to evaporation from side gap of columns, upward flow due to vapor phase movement of moisture, and the collapse of macropores resulting from soil packing.