Maziar Ramezani

Numerical simulation of sheet stamping process using flexible punch

Abstract Different from the conventional stamping process, rubber forming uses a rubber pad contained in a rigid box to act as a punch. The main attraction of the process is its simplicity, and it can be used for prototype development or for low-volume production. In this study, an axisymmetric rubber-pad forming operation is investigated via numerical simulations and experiments. Some key process parameters, such as rubber material, hardness of flexible punch, stamping velocity, rubber-pad thickness, and friction are studied in detail. Good correlation is achieved between the finite element predicted and experimentally measured thickness—thinning in the formed part. Stress and strain distributions in the specimen are investigated numerically during the process using ABAQUS/Standard.

60NiTi: A Review of Recent Research Findings, Potential for Structural and Mechanical Applications, and Areas of Continued Investigations

Recent advances in the manufacture and processing of high purity NiTinol 60 (60 wt% Ni–40 wt% Ti) has spurred a renewed interest in the use of this alloy for structural and mechanical component applications. NiTinol 60 (60NiTi) exhibits excellent corrosion resistance, can be hardened to high levels, has a low elastic modulus and extensive elastic range that imparts high mechanical contact load resilience. It is dimensionally stable, has good bio-compatibility, can be machined into precision components and is non-magnetic. This unique set of characteristics make the intermetallic 60NiTi suitable for a wide variety of applications in the marine, medical, aerospace and food processing industries. This article surveys and reviews a broad range of historic and recent publications on 60NiTi to highlight what is known and areas that require further study. In particular, recent results indicate a dichotomy in friction and wear behavior. Under good lubrication (liquid or solid) both friction and wear are low but in dry un-lubricated sliding, wear exceeds that of other materials such as steel that have comparable hardness. This unexpected behavior is proposed as an important topic for future investigations before any of widespread adoption in engineering applications.

Pull-out behavior of galvanized steel strip in foam concrete

The interface and bond between concrete and reinforcing steel are the most fundamental problems of reinforced concrete structures. In this paper, the pull-out strength of galvanized steel strips with different geometries and hole patterns in foam concrete blocks are investigated experimentally and numerically. Foam concrete mixtures of 1,200-kg/m3 density were obtained by mixing cement and water in a mortar mixer together with ultrafoam as the foaming agent and Quick-Gel as the viscosifier. A theoretical model is developed to predict the bond-slip relationship between the strip and the concrete. This model is further implemented in a finite element simulation of the pull-out tests through the ABAQUS user subroutine. The results show good correlation between experimental, theoretical, and finite element simulation analyses. The influence of the steel strip geometries on the maximum pull-out force is also studied, and it was found that the strips with the greatest hole area, hole diameter, and circumference areas have higher pull-out forces and the increase is nearly linear.

High strain-rate bulge forming of sheet metals using a solid bulging medium

Abstract The biaxial bulge-forming of sheet metals is a standard test to evaluate the formability and mechanical behaviour of materials. A new dynamic bulge-testing method is simulated and analysed in this study that can be performed on a conventional split Hopkinson pressure bar (SHPB) system. The aim of this work is to develop a numerical and theoretical technique for the analysis of materials and structures, which are dynamically loaded and subjected to the different levels of strain rates. The commercial finite element code ABAQUS/Explicit has been selected as the numerical test bed for the simulation of the dynamic bulging test. In the new bulge-forming technique, flexible rubber is used as the pressure-carrying medium instead of hydraulic fluid. The theoretical analysis is based on conventional hydraulic bulge test principles and SHPB relations. To verify the accuracy of the developed technique, analytical and finite element methods are compared and show good correlation with each other.

Investigation of Polyurethane Bonding to Steel in Sandwich Panels

Sandwich panels made of thin and stiff skins, connected by a thick and soft core are widely used in load-bearing components mainly due to their high strength to weight ratio. To improve the reliability in using sandwich beams, it is necessary to understand their responses under external mechanical and environmental stimuli. This paper investigates the construction of steel-polyurethane-steel sandwich panels and their mechanical properties. Key properties of a sandwich structure are the adhesion between the skins and the sandwich material, and the load transfer from the outer skin to the inner skin. Lap shear specimens were selected to give an indication of the bond strength of the polyurethane to steel, whilst three point bend test specimens were selected to indicate the degree of load transfer between the skins and the bending resistance provided by the sandwich structure.

Reciprocating Sliding Wear Behavior of 60NiTi As Compared to 440C Steel under Lubricated and Unlubricated Conditions

ABSTRACT 60NiTi is a hard (∼60 HRC) and highly corrosion-resistant intermetallic with a relatively low elastic modulus (∼100 GPa). In addition, this alloy exhibits a high compressive strength (∼2,500 MPa) and a high elastic compressive strain of over 5%. These attributes make this alloy an attractive candidate to be employed in structural and mechanical component applications. However, sliding wear behavior of this intermetallic has not yet been studied in a systematic way. In this study, lubricated and unlubricated reciprocating sliding wear behavior of 60NiTi is compared to 440 C steel as a conventional bearing and wear-resistant alloy. Results of experiments carried out under different loads show that 60NiTi, despite having a higher hardness, exhibits a significantly inferior wear behavior under dry conditions in comparison to 440 C steel. These unexpected results indicate that 60NiTi does not follow conventional wear theories where the wear of materials has an inverse relationship to their hardness. On the other hand, under lubricated conditions with castor oil and a synthetic gear oil, 60NiTi exhibits low specific wear rates. These results exhibit the importance of proper lubrication in sliding mode applications where 60NiTi is exploited as a wear-resistant alloy.

High Strain Rate Compressive Behaviour of Selective Laser Melted Ti-6Al-4V

Ti-6Al-4V alloy is one of the most important engineering alloys, combining attractive properties with inherent workability. The aim of this study is to investigate the effect of strain rate on the compressive mechanical properties of Ti6Al4V alloy manufactured by a selective laser melting process. The mechanical tests were performed by means of a compression split Hopkinson pressure bar apparatus under high strain rate ranging from 1400 s-1 to 4500 s-1. The true stress-strain curves obtained from static and dynamic compressive tests show strain rate sensitivity from quasi-static (peak strength 1300MPa) to high strain rate (peak 1500 MPa). Within the high strain rate range tested, the strain rate sensitivity is not remarkable. The fractographic analysis shows a relatively smooth and smeared fractured surface along with a dimple like structure. The observation of elongated dimples confirms the operation of a dynamic shear failure mechanism for the additively manufactured Ti-6Al-4V parts.

Experimental and numerical analysis pull-out strength of steel strip in foam concrete

The structural performance of a reinforced concrete is influenced by the properties of the reinforcing element and the concrete interface. Therefore, investigating the pull-out strength and bond stress vs. slip relationship between components of the reinforced concrete are very important. This paper presents a numerical method to study the pull-out behaviour of galvanised steel strips in aerated concrete. A local bond-slip relationship is determined using experimental and theoretical analyses and is then implemented to the finite element simulation through the user-defined subroutine of ABAQUS software. The effect of strip geometry and mechanical properties of the aerated concrete on the pull-out force is also investigated. Comparison between the experimental, theoretical and FE simulation results shows very good agreement. It was shown that a trilinear bond-slip model is suitable for the modelling of steel strip and concrete interface.

Introduction to sheet metal forming processes

In the last decades several innovative sheet metal forming processes have been introduced. One of the categories of these innovative techniques is the use of unconventional tools such as fluid, gas, viscous medium and elastomer pads as the pressure carrying agents. These flexible tools have been used increasingly in recent years in the design of metal forming processes. The fundamentals of four flexible-die forming techniques, i.e. hydroforming, hot metal gas forming, viscous-pressure forming and rubberpad forming are explained in this chapter and the advantages and drawbacks of each process are noted.

An Investigation on Reasons Causing Inferiority in Unlubricated Sliding Wear Performance of 60NiTi as Compared to 440C Steel

Abstract 60NiTi is gaining recognition as an alternative to 440C steel in ball bearing components due to its intrinsic corrosion resistance and unusually high static load capacity. 440C steel and 60NiTi exhibit comparable Rockwell hardness and would be expected to exhibit similar sliding wear behavior using hardness based models. However, results show that under unlubricated sliding conditions, 60NiTi shows inferior wear properties than 440C steel. In this study, a series of indentation and single pass scratching experiments are conducted to elucidate the reasons behind this unexpected observation. Moreover, sliding wear tests carried out under moderate and extreme tensile stress conditions were used to identify sliding conditions under which these materials exhibit similar and dissimilar behavior. The results show that 440C steel exhibits more microscopic plasticity than 60NiTi, halting the propagation of generated tensile microcracks. In contrast, the intrinsic brittleness of 60NiTi leads to the formation and growth of microcracks between the shear bands causing subsequent wear particle generation. These lead to the occurrence of wear through more aggressive abrasion processes in 60NiTi than 440C steel. These findings help explain why 60NiTi performs well when lubricated. 60NiTi is expected to tolerate ∼912 MPa tensile stress before yielding. Under good lubricated conditions where a perfect lubricating film is formed, friction induced tensile stresses fall below the tensile strength of 60NiTi and wear is prevented. However, inadequate lubrication combined with high contact stress leads to damage and wear.