Journal of Manufacturing Processes 15 (2013) 219–226 Contents lists available at SciVerse ScienceDirect Journal of Manufacturing Processes j ourna l h o me page: www.elsevier.com/locate/manpro Technical paper Modeling tensile strength of materials processed by accumulative roll bonding Justin L. Milner a,∗ , Cristina Bunget a , Fadi Abu-Farha a , Thomas Kurfess b , Vincent H. Hammond c a Department of Automotive Engineering, Clemson University, Greenville, SC 29607, USA b Department of Mechanical Engineering, Georgia Institute of Technology, GA 30332, USA c US Army Research Laboratory, Aberdeen Proving Ground, MD 21005, USA a r t i c l e i n f o Article history: Received 30 August 2012 Received in revised form 14 January 2013 Accepted 4 February 2013 Available online 13 March 2013 Keywords: Accumulative roll bonding Severe plastic deformation Strengthening modeling a b s t r a c t Nanostructured materials are a relatively new class of materials that exhibit advanced mechanical prop- erties, thus improving performance and capabilities of products, with potential applications in the automotive, aerospace and defense industries. Among the severe plastic deformation (SPD) methods currently used for achieving nanoscale structures, accumulative roll bonding (ARB) is the most favorable method to produce grain refinement for continuous production of metallic sheets at a bulk scale. In this article, a model that describes the evolution of material strength due to processing via accumu- lative roll bonding was developed. ARB experiments were conducted on CP-Ti Grade 2 at a selected set of conditions. The results showed significant grain refinement in the microstructure (down to ∼120 nm) and a two-fold increase in tensile strength as compared to the as-received material. The developed model was validated using the experimental data, and exhibited a good fit over the entire range of ARB processing cycles. To further validate the model and ensure its robustness for a wider array of materials (beyond CP-Ti), a review of efforts on ARB processing was carried out for five other materials with different ini- tial microstructures, mechanical properties, and even crystalline structures. The model was still able to capture the strengthening trends in all considered materials. © 2013 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved. 1. Introduction Processing of metals through the application of severe plastic deformation (SPD) is well substantiated for the production of mate- rials with a grain size in the range of submicrometer to nanometer [1,2]. The main objective of the SPD techniques is to generate very large plastic strains within the material, which results in dislocation structures that reorganize to form cells, subgrains, and large-angle grain boundaries, thus leading to progressive grain refinement [3]. The grain refinement confers unique physical and mechani- cal properties such as high strength [4,5], as well as the potential for achieving superplasticity at low temperatures [6–8]. The final grain size obtained from SPD methods depends on the material and processing routes conducted. There are several different man- ufacturing methods of SPD available, such as equal-channel angular pressing (ECAP), high-pressure torsion (HPT), and accumulative roll bonding (ARB) to name a few. ARB is an SPD technique proposed as a method for continuous production of bulk sheets with advanced properties [9]. ARB, which was developed by Saito et al. [10], aims to synthesize ultra-fine grained and nanocrystalline structures with prevail- ing high-angle grain boundaries in metallic materials through an ∗ Corresponding author. Tel.: +1 814 602 7062; fax: +1 864 283 7208. E-mail address: jlmilne@clemson.edu (J.L. Milner). inexpensive and industrially feasible manner (utilizing a conven- tional metal rolling facility). During the ARB process, the metallic strips are repeatedly cleaned, stacked, deformed/bonded, and cut in two. The initial workpiece may consist of two or more stacked layers which are bonded during the rolling process and creates a bulk material/composite. To achieve good bonding of the layers, the surfaces must be treated, usually by degreasing and wire brushing prior to stacking. This is done to remove any debris on the surface which may hinder the bonding between the layers. Furthermore, the layers are roughened to increase friction and surface area which reduces relative sliding between the layers and increases adhesion. Rolling is usually performed at a 50% reduction in thickness, induc- ing severe plastic deformation, during each cycle. After rolling, the strip (elongated to twice its original length) is cut in two, cleaned, and stacked one on top of the other, resulting in a strip with identi- cal dimensions as the starting workpiece. This process is repeated until the target grain size is achieved and, thus, the desired mate- rial properties are realized. Moreover, the ARB process is capable of producing metallic multi-layered composites consisting of alter- nating metal layers or reinforced metal layers that can dramatically improve a wide range of mechanical properties. The resulting increase in the material’s strength produced by the ARB process is predominantly due to strain hardening by dis- locations and grain boundary strengthening (or grain refinement). Previous studies have suggested that the formation mechanism of grain refinement during ARB can be explained in terms of grain 1526-6125/$ – see front matter © 2013 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jmapro.2013.02.001