Mohammad A. Irfan

Novel experimental techniques for investigating time resolved high speed friction

Abstract The paper presents some recent advances in experimental methods to investigate the phenomenon of high speed friction. In particular, two novel experimental methods are employed in the present study: (a) the plate impact pressure–shear friction experiment, and (b) the torsional Kolsky bar friction experiment. Using these experimental configurations, dynamic frictional characteristics of Carpentor Hampden tool-steel/Ti6Al4V and Carpenter Hampden tool-steel/7075-T6 Al are investigated under conditions of high interfacial normal pressures (100 MPa to 2 GPa), high slip speeds (1 to 60 m/s) and elevated temperatures. The results of these experiments provide some new insights into the role of the applied normal pressure, interfacial slip speeds, interfacial temperature, and the surface roughness in controlling the tribology of dry sliding interfaces.

Dynamic deformation and fracture behavior of novel damage tolerant discontinuously reinforced aluminum composites

Abstract Extrinsically toughened discontinuously reinforced aluminum composites are processed with the objective of enhancing damage tolerance of conventional particle reinforced aluminum composites. The approach consists of producing a composite microstructure in which discrete ductile phases have been incorporated into the particle reinforced metal matrix via traditional powder processing routes. The present study focuses on investigating the effects of volume fraction and flow strength of the ductile phase reinforcements in determining dynamic deformation and fracture characteristics of these extrinsically toughened composites. The dynamic compression behavior of the composites is examined by employing the split Hopkinson pressure bar. The measured dynamic stress–strain response of the composites is correlated with the macro- and micro-damage mechanisms inferred from post examination of the impacted specimens. The dynamic fracture characteristics of the composites are obtained by impact loading pre-cracked three point bend specimens in a modified Hopkinson bar apparatus. The measured load-point force versus load-point displacement curves are used to, (a) estimate the energy required for dynamic crack initiation, and (b) understand the interaction of the dynamically propagating crack tip with the ductile phase reinforcements. The results indicate that the extrinsically toughened DRA composites absorb significantly greater energy during the crack propagation as compared to the conventional DRA composites. Also, the level of extrinsic toughening introduced in the composites is affected by the location, volume fraction and mechanical properties of the ductile phase reinforcements. Amongst the relatively larger volume fraction ductile-phase reinforced composites, the ductile phase reinforcements comprising low flow strength commercial purity aluminum fail primarily in a ductile manner, whereas the ductile phase reinforcements comprising high strength Al alloy fail in a cleavage manner by inter-granular fracture.

State and Rate Dependent Friction Laws for Modeling High-Speed Frictional Slip at Metal-on-Metal Interfaces

In the present paper the applicability of state and rate dependent friction laws in describing the phenomena of high speed slip at metal-on-metal interfaces is investigated. For the purpose of model validation, results of plate-impact pressure-shear friction experiments were conducted by Irfan in 1998 and Irfan and Prakash in 2000 using a Ti6Al4V and Carpenter Hampden tool-steel tribo pair are employed. In these experiments high normal pressures 1–3 GPa and slip speeds of approximately 50 m /s were attained during the high-speed slip event. Moreover, these experiments were designed to investigate the evolution of friction stress in response to step changes in normal pressure and also in the applied shear stress during the high-speed slip event. A step drop in normal pressure is observed to result in an exponential decay of the friction stress to a new steady-state characteristic of the current normal pressure and the current slip velocity. A step drop in applied shear stress is observed to lead to an initial drop in friction stress, which later increases toward a new steady-state friction stress level. In response to the step drop in applied shear stress the slip velocity initially increases and then decreases to a new steady-state level consistent with the new friction stress level. A modified rate and state dependent friction model that employs both velocity and normal stress dependent state variables is used to simulate the experimental results. A good correlation is found between the experimental results and the predictions of the proposed state and rate dependent friction model. DOI: 10.1115/1.2401217

Assembly Features: Definition, Classification, and Instantiation

Form features are defined for different aspects. One of the aspects is robot assembly. Robot assembly process is defined and then simulated using form features defined on the parts of the product to be assembled. Owing to this, form features are used here in the definition and mathematical representation of assembly feature while using the concept of assembly intent. Moreover, a classification and instantiation of assembly features is provided that can help in the integration of CAD and assembly planning

New solar radiation Atlas for Saudi Arabia

The paper presents one of the first discussions on the new Solar Atlas of Saudi Arabia which was launched in Feb 2104. The solar atlas data comprises of live data recording from 70 stations across the country. The current paper presents the solar maps of the country through various months. The solar maps show that the DNI in various regions of the country ranges from approximately 9.0 kWh/m2/ day in the summer months to 5.0 kWh/m2/ day in the winter months. GHI in various regions can go as high as 8.3 kWh/m2.A comparison of local temperatures recordings in 2013 shows good agreement with the GEO Satellite data. Finally a brief is presented about the recording station at Qassim University and its results are discussed.

Transient thermo-mechanical interactions during high-speed slip at metal-on-metal interfaces

Abstract The paper describes results obtained from plate-impact pressure-shear friction experiments to investigate the phenomena of high-speed slip at metal-on-metal interfaces. Using a CH tool-steel/Ti-6Al-4V tribo-pair the authors have studied the effects of normal pressure, slip-speed, temperature and surface roughness on the evolution of the dynamic slip-resistance. Moreover, a finite-element procedure is developed to simulate the evolution of thermo-mechanical fields and understand their relationship to the observed slip response. Next, the pressure-shear friction experiments are extended to investigate the behavior of CH tool-steel/7075-T6 Al alloy tribo-pair. This material combination allows dynamic friction characteristics to be studied in the near-melt and the fully melt temperature regime of the lower-melting-point metal (7075-T6 Al alloy) comprising the tribo-pair. Besides providing information on the slip-velocity versus friction-stress relationship under extreme interfacial conditions, the experiments provides critical information on the shearing resistance of confined molten metal films under high pressures and extremely high shearing rates.

Dynamic crack propagation and arrest in rapid prototyping material

Purpose – The purpose of this paper is to find the response of micro‐layered rapid prototyping material under impact loading.Design/methodology/approach – A modified Hopkinson Bar was used to impart impact loading in velocities ranging from 2‐7 m/s. Strain gages and stress wave theory were employed to calculate the load‐point force and displacement. Hence the dynamic crack initiation and propagation energies were calculated.Findings – It was found that the crack deflection and inter layer delamination mechanisms lead to greater absorption of crack propagation energy and hence offer better resistance to crack propagation as compared to monolithic acrylonitrile butadiene styrene (ABS).Practical implications – The finding will lead to greater confidence for the use of rapid prototypes as direct‐use parts subjected to low velocity impact.Originality/value – Although the static properties of ABS material used in rapid prototyping are well documented, this paper is one of the first reported researches in measur...

Assembly Features: definition, classification, and usefulness in sequence planning

Unique definition and classification of assembly feature are presented. Assembly features definition is provided using the concept of assembly intents. Assembly features classification is done based on useful assembly-specific information. Assembly features provide information that result in a smaller number of assembly sequences that have to be checked in assembly sequence optimisation. Due to the reduction in assembly sequences, AND/OR graph not only reduces considerably but also becomes very simple. This can result in a significant reduction in the computation time for assembly sequence planning. Real-life examples are given to demonstrate how assembly features are useful in sequence planning.

Impact Behavior of Extrinsically Toughened Discontinuously Reinforced Aluminum Composites

Discontinuously reinforced aluminum (DRA) composites with enhanced fracture toughness have recently been developed at ALCOA. The approach consists of producing a composite microstructure in which discrete ductile phases have been incorporated into the DRA through traditional powder processing routes. In the present paper, the high strain rate behavior of these toughened composites is investigated by obtaining (i) the dynamic flow characteristics at various levels of elevated strain rates using a split Hopkinson compression bar, and (ii) energy absorption during dynamic crack initiation and crack propagation using three-point bend specimens loaded on a modified Hopkinson bar configuration.

Frequency analysis of volumetric porosity in aluminum castings at high and low cooling rates

Abstract Three dimensional porosity analysis was conducted using computed tomography for Al-Si alloy castings. Statistical analysis was performed to compare the porosities of the castings at high and low cooling rates. It was observed that the cooling rates strongly affect the formation of pores for both small and large pores. The incidence of small pores measuring 0.00003 mm3 to 0.0004 mm3 can be up to six times higher in castings formed at low cooling rates. For large pores measuring 300 μm to 360 μm, it was observed that lower cooling rates give rise to larger pores, which are known to be detrimental to castings as potential failure initiation sites.