Mani Maran Ratnam

The relationship between substrate roughness parameters and bond strength of ultra high-performance fiber concrete

The bonding that exists between the old concrete and the new concrete depends largely on the quality of substrate surface preparation. The accurate representation of substrate surface roughness can help determine very precisely the correct bonding behavior. In this work, an experimental investigation was carried out to quantify the normal concrete (NC) substrate roughness parameters and evaluate their relationship with the bonding performance of ultra high-performance fiber concrete (UHPFC), used as a repair material. The bond strength was quantified based on the results of the pull-off test, splitting cylinder tensile test, and the slant shear test. Three types of NC substrate surface preparation were used: as-cast (without surface preparation) as reference, wire-brushed, and sand-blasted (SB); the roughness of which was determined using an optical three-dimensional (3D) surface metrology device (Alicona Infinite Focus). It was observed from the result of the pull-off test that failure occurred in the substrate, even though adequate substrate surface roughness was provided. Moreover, analysis of the splitting cylinder tensile and slant shear test results showed that the substrate surface preparation method had a significant influence in bonding strength between UHPFC and the NC substrate. The composite UHPFC/NC substrate having a SB surface behaved closely as a monolithic structure under splitting and slant shear tests. An excellent correlation (R 2 > 85%) was obtained between the substrate roughness parameters and the results of the splitting cylinder tensile and slant shear tests.

Wear performance and mechanical properties of 80 wt-%Al2O3/20 wt-%YSZ cutting inserts at different sintering rates and soaking times

Abstract A series of ceramic tools with different sintering conditions based on zirconia toughened alumina (ZTA) was produced. Experiments on ZTA cutting tools with different sintering rates and soaking times were carried out. Cutting inserts with80 wt-% alumina (Al2O3)/20 wt-% yttria stabilised zirconia (YSZ), in which Al2O3 and YSZ powders are mixed, was compacted and sintered at 1600°C using solid state sintering. Mechanical and physical properties such as wear resistance, hardness HV30, fracture toughness and microstructure were analysed. Mild steel (AISI 1018) was used as the workpiece for wear resistance study. It was observed that a slower sintering rate induces better mechanical properties on the cutting tool. With increasing the sintering rate from 2 to 8°C min−1, the wear area increased from 0·0443 to 0·118 mm2. The hardness of the samples decreased from 1563·5 to 1313·8 HV, while the fracture toughness also decreased from 4·709 to 3·95 MPa m1/2. For the effect of increasing sintering soaking time from 120 to 300 min, the wear area decreased from greatest (0·1939 mm2) to lowest (0·0797 mm2). Similarly, microstructural coarsening within ZTA was found to produce a fracture toughness increase from 3·95 to 6·374 MPa m1/2. The influence of phase polymorphic transformation on the improvement of the mechanical properties is discussed.

Error-based autofocus system using image feedback in a liquid-filled diaphragm lens

A liquid-filled diaphragm (LFD) lens system that uses image feedback for automatic focus control has been designed and developed. The edge slope width (ESW) of the pixel intensity profile across a binary target was selected as the focus measure parameter. An algorithm was developed to achieve single- and dual-direction autofocus control. An improved autofocus method, which is based on the error between the expected ESW value for a focused image and the ESW value for the current (unfocused) image, was introduced to improve the performance of the system. An empirical equation of the focus measure error was used to predict the number of autofocus operation steps required to approach a near-focus region. A stepper motor was used for actuating a syringe-driven pump mechanism that injects or withdraws fluid into (or out of) the fluid lens chamber. The lens diaphragm was made of polydimethylsiloxane (PDMS) polymer that covers the fluid chamber. A monochrome CCD camera was attached to the LFD lens to capture live images of the target. The autofocus experiments carried out using the new differential error-based algorithm proved the viability of the algorithm in determining the near-focus region. A maximum reduction of time operation was also recorded to be 40 s in comparison with the normal autofocus algorithm.

Force‐guided robot in automated assembly of mobile phone

This paper describes how force‐guided robot can be implemented in the automated assembly of mobile phone. A case study was carried out to investigate the assembly operations and strategies involved. Force‐guided robot was developed and implemented in the real environment. Proportional‐based external force control with hybrid framework was developed and implemented to perform the compliant motion. In order to perform assembly operations, three basic force‐guided robotic skills are identified. These are stopping, alignment and sliding skills, where the motions are guided by the force feedback. The force‐guided robotic skills are combined and reprogrammed with fine motion planning to perform notch‐locked assembly. The system is optimized for high assembly speed while considering the constraints and limitations involved.

Large In‐plane Deformation Mapping and Determination of Young's Modulus of Rubber Using Scanner‐Based Digital Image Correlation

We propose a novel scanner-based digital image correlation (DIC) method to determine the full-field in-plane displacement as well as the Young’s modulus of elastomeric materials at strains up to 350%. A low-cost charged-couple device flatbed scannerwas used as the image acquisition device instead of a digital camera in the conventional DIC method. A motorized loading fixture was designed to act as the specimen clamp as well as the tensile load applicator. The rubber specimens weremade according to the ASTM:D412-06a standard andmounted into the fixture. Each specimen was scanned at increasing loads and the images were processed to obtain the full-field displacement maps using incremental cross-correlation algorithm. The Young’s modulus of the rubber at strains of 50–350% obtained using the scanner-based DIC method was compared with those obtained from a universal tensile test machine. The comparison shows a maximum deviation in Young’s modulus of 8.9 at 150% strain. The high-resolution flatbed scanner coupled with the built-in lighting was found to be an effective tool for low-cost DIC application for large deformation materials.

An Approach for Nonlinear Damping Characterization for Linear Optical Scanner

Vibratory systems that are used in linear optical scanners are significantly influenced by the properties of the surrounding fluid. Although, the dominant energy loss in scanner vibrations is caused by viscous effects, especially in non-microelectromechanical system (MEMS) scanners, the relative importance of viscous damping model is not well studied. In this study, a piece-wise method for calculating the damping ratio with logarithmic decrement to produce a numerical model which is able to predict the free response of a linear optical scanner is developed. The damping ratio function used in the model was derived by comparing and minimizing the deviation between the amplitude predicted by numerical model and the experimental data. The efficiency of this approach was tested on the basis of a torsional spring scanner. The results show significant improvement whereby the proposed model predicted the free response with a deviation of only 8% while the general exponential damping model produced a deviation of 20%.

Effect of Mo on the High-Temperature Creep Resistance and Machinability of a Recycled Al-Alloy with High Iron Impurity

Reported work focuses on the effect of morphology of the Fe-rich intermetallic phases on the machinability of Al-alloy containing >2wt.% Fe, obtained from automotive scrap. Effect of Mo addition on the microstructure, high-temperature impression creep and thereby the machinability of the Al-recycled alloy were studied. The machinability of the recycled alloy was estimated by investigating the built-up-edge (BUE) and surface roughness (Ra). SEM-EDS and TEM-SADP studies have shown that the crystal structure (BCC) of the Al8Fe2Si phase remained unchanged; however, Mo replaced few Fe atoms with little effect on the lattice dimension. It has been found that the addition of Mo to the recycled alloy suppresses the formation of β-phase (Al5FeSi) by suppressing the peritectic transformation of α (Al8Fe2Si) phase. Such suppression is found to improve the high-temperature creep resistance and the machinability with the increase in the Mo addition level.

An Improved Method of Projected Area Determination in Nanoindentation Using Image Processing With Sub-Pixel Edge Location

We propose a novel approach to determine the precise indent area using image processing with sub-pixel edge location in nanoindentation hardness testing. The impressions made by nanoindentation on copper and mild steel specimens were captured using a high-resolution optical microscope. Each indent area was cropped out and subjected to pixel-level edge detection using the Canny operator. Based on the detected edge the invariant moment sub-pixel edge location method was applied to determine the precise location of the edges of the indent using combined vertical and diagonal scanning. The projected area was then determined directly from the enclosed contour to sub-pixel accuracy. The hardness value was determined by dividing the load with the area determined using the proposed approach. Comparison of the hardness values was made using the area determined by sub-pixel edge location and that determined from the nanoindentation tests showed a maximum difference of about 3.74% for the copper specimen and 4.17% for mild steel specimen. Unlike in the actual nanoindentation test, the proposed method of determining hardness does not assume that the indentation area is triangular, thus resulting in higher accuracy hardness values.

The Effects of Cr2O3 Addition on Fracture Toughness and Phases of ZTA Ceramic Composite

Fracture toughness and phases of ceramic composites produced from alumina, yttria stabilized zirconia and chromia oxide system was investigated. The Cr2O3 weight percent was varied from 0 wt% to 1.0 wt%. Each batch of composition was mixed, uniaxially pressed 13mm diameter and sintered at 1600 C for 4 h in pressureless conditions. Studies on on their mechanical and physical properties such as Vickers hardness and fracture toughness were carried out. Results show that an addition of 0.6 wt% of Cr2O3 produces the best mechanical properties. Results of the highest fracture toughness is 4.73 MPa.m1/2,

Simulation of surface roughness and topography in finish turning using digital image subtraction

Most surface roughness prediction models based on mathematical approach assume a geometrically well-defined nose profile, i.e. either circular or elliptical. Such simple models cannot be applied in cases where the tool nose develops different wear patterns or have non-geometric arbitrary profile, such as those caused by manufacturing tolerances in the nose radii. In this study, a digital simulation method using binary image subtraction is used to generate the work piece surface topography, and from which the common roughness parameters of the work piece are determined. Comparison of the digital simulation method with the theoretical models using ideal nose shape shows a maximum difference of 4.7% in the average roughness value.