PSI - Issue 14

Tulsi Chouhan et al. / Procedia Structural Integrity 14 (2019) 883–890 Author name / Structural Integrity Procedia 00 (2018) 000–000

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1. Introduction The significance of powder size and ball milling parameters in powder metallurgy made metallic components is vital. With increasing powder size the mechanical performance of the finished component generally diminishes. Likewise, reducing powder mean diameter enhances the physical and mechanical properties of the component, fabricated by powder metallurgy route. Aluminum owing to its good heat and electricity conduction, moderate to high strength and modulus coupled with low specific gravity has widely been used for applications ranging from automobile, defense to aerospace. Majority of applications only demand quasi-static characterization of metals, but applications from automobile and aerospace also demand the high strain rate characteristics of the metal being used. Formation of low-density metal components using a relatively cost-efficient method is always valued. A number of methods have been attempted to produce low-density metallic components (Peroni et al. 2012)(B. Zhang et al. 2016). Peroni et al. reported that to reduce the weight of automotive and aerospace components Aluminum foams can be a good choice. They developed Aluminum foams through powder metallurgy route and used SHPB to study the compressive dynamic behaviour of Aluminum foam and reported poor strength of porous Aluminum. Zhang et al. (B. Zhang et al. 2016) reported that incorporation of 80  m cenospheres results in 90% higher strength of Aluminum matrix composite compared to 160  m cenospheres. The rate-dependent properties of different materials produced by various techniques have been tested over the last decades. Generally, most of the metals exhibit rate dependent behavior. The rate dependency here refers to increasing mechanical performance of metals as a function of the increasing rate of loading (Behm et al. 2016). This phenomenon of rate dependency is observed not only in metals but also in metal matrix composites, fiber reinforced plastic composites and ceramic reinforced composites (Tan et al. 2007). The effect of mean powder diameter in powder metallurgy made specimen plays a vital role in defining the mechanical properties of a specimen. Razavi-Tousi et al. (2015) studied the effect of ball size on aluminum powder and reported that during initial few hours of milling due to the formation of disc-like structures the average powder size increases before crushing of these large sized powder particles into smaller size powder due to high ball milling time. They also inferred that for any given ball to powder weight ratio there is a limiting powder size which can be attained, beyond which an insignificant reduction in powder size is reported. The rate-dependent behavior of Al under high strain rate loading is presented by Zhang et al. (2008). With increasing strain rate of loading from 600 /s to 7000 /s, the variation in strength characteristics is reported in the form of increasing material properties. Cowper Symonds model was used to fit a model on the material under consideration and a satisfactory match is reported with experimental findings. Literature proves that powder metallurgy can be a good choice for the cost-efficient development of Aluminum matrix based composites. Simultaneously, increasing porosity by the generation of voids or addition of foreign bodies like cenospheres can further aid in attaining the desired properties. Therefore, the aim of presented work was to develop porous Aluminum matrix composite by powder metallurgy method using a relatively cost-efficient scheme. To understand the effect of ball milling a comparative study is conducted between Al powder compacted as received versus powder milled for 24 hours. Also, density variation using high rock salt percent is attempted. To remove the salt from specimen the Al specimens were kept in a boiling water bath. The high strain rate studies were conducted on the Split Hopkinson Pressure Bar (SHPB) set-up.

Nomenclature  r

reflected strain

transmitted strain

 t E

C 0 A B L s

elastic wave velocity in the bars cross-section area of the bar

Young’s modulus of elasticity of bar material cross-section area of the specimen

A S

specimen length

t

time duration Aluminum

SHPB split Hopkinson Pressure Bar MMC Metal Matrix Composite

Al