Studies on Friction and Formation of Transfer Layer in HCP Metals

Surface texture plays an important role as it predominantly controls the frictional behavior and transfer layer formation at the contacting surfaces. In the present investigation, basic studies were conducted using inclined pin-on-plate sliding tester to understand the role of surface texture of hard material on coefficient of friction and transfer layer formation when sliding against soft materials. HCP materials such as pure Mg and pure Zn were used as pins while 080 M40 steel was used as plate in the tests. Two surface parameters of steel plates — roughness and texture — were varied in the tests. Tests were conducted in ambient conditions under both dry and lubricated conditions. The morphologies of the worn surfaces of the pins and the formation of transfer layer on the counter surfaces were observed using a scanning electron microscope. It was observed for both the pin materials that the occurrence of stick-slip motion, the transfer layer formation and the value of coefficient of friction as well as its two components, namely, adhesion and plowing, depend primarily on surface texture. The effect of surface texture on coefficient of friction was attributed to the variation of plowing component of friction for different surfaces. Both the plowing component of friction and amplitude of stick-slip motion were highest for the surface texture that promotes plane strain conditions while these were lowest for the texture that favors plane stress conditions at the interface.

The Model Eliciting Activity (MEA) Construct: Moving Engineering Education Research Into the Classroom

A growing set of “professional skills” including problem solving, teamwork, and communications are becoming increasingly important in differentiating U.S. engineering graduates from their international counterparts. A consensus of engineering educators and professionals now believes that mastery of these professional skills is needed for our graduates to excel in a highly competitive global environment. A decade ago ABET realized this and included these skills among the eleven outcomes needed to best prepare professionals for the 21st century engineering world. This has left engineering educators with a challenge: how can students learn to master these skills? We address this challenge by focusing on models and modeling as an integrating approach for learning particular professional skills, including problem solving, within the undergraduate curriculum. To do this, we are extending a proven methodology — model-eliciting activities (MEAs) — creating in essence model integrating activities (MIAs). MEAs originated in the mathematics education community as a research tool. In an MEA teams of students address an open-ended, real-world problem. A typical MEA elicits a mathematical or conceptual system as part of its procedural requirements. To resolve an MEA, students may need to make new connections, combinations, manipulations or predictions. We are extending this construct to a format in which the student team must also integrate prior knowledge and concepts in order to solve the problem at hand. In doing this, we are also forcing students to confront and repair certain misconceptions acquired at earlier stages of their education. A distinctive MEA feature is an emphasis on testing, revising, refining and formally documenting solutions, all skills that future practitioners should master. Student performance on MEAs is typically assessed using a rubric to measure the quality of solution. In addition, a reflection tool completed by students following an MEA exercise assists them in better assessing and critiquing their progress as modelers and problem solvers. As part of the first phase a large, MEA research study funded by the National Science Foundation and involving six institutions, we are investigating the strategies students use to solve unstructured problems by better understanding the extent that our MEA/MIA construct can be used as a learning intervention. To do this, we are developing learning material suitable for upper-level engineering students, requiring them to integrate concepts they’ve learned in foundation courses while teasing out misconceptions. We provide an overview of the project and our results to date.

The Role of Laboratory Experiments in Engineering Education

The role of students experience in laboratory tests as a part of their engineering education is discussed. Nowadays, when computer simulations become an important tool in engineering design, problems solution, and research, students may loose the touch of real-world hardware and challenges. Hence, exposure to experimental work is very significant. It is proposed that at the advanced stages of the first degree studies, experiments related to specific courses will be incorporated as a part of the course material. It is also believed that in studies towards higher degrees, the combination of experimental research with theoretical modeling and analysis is an excellent introduction for the future professional career.

Modeling of Surface Topography for Reduced Friction

The aim of the present research was to investigate surface topography in terms of different surface roughness parameters and to correlate surface topography change to friction of contact surfaces. For this purpose, different 100Cr6 plate samples with different surface topography were prepared. Using different grades and combinations of grinding and polishing samples with similar Ra values, but different Rku and Rsk values were obtained. To evaluate influence of roughness parameters on friction and wear, dry and lubricated pin-on-disc tests were carried out under different contact conditions. Test results indicate that high Rku and negative Rsk values lead to decrease in friction. To investigate the effect of surface texturing on surface roughness parameters, real roughness profiles were virtually altered to achieve virtually textured surfaces. Using NIST SMATS softgauge for calculation of surface roughness parameters, virtually altered roughness profiles were investigated in terms of texture size, shape and spacing, and their influence on surface roughness parameters, especially on skewness and kurtosis. Lower diameter, higher spacing and wedge-shaped dimples reflect in higher Rku and more negative Rsk parameters.

Experimental Determination of Optimal Speeds for Alloy Steels in Plane Turning

In machining, speeds play vital role. The operator should know exactly the speed at which machining should be performed to get the required surface finish. In this paper, an attempt is made to determine the optimal cutting speed for machining of alloy steels. Three work piece materials having different hardness are taken and machined using a round nose tool with a coated tip. The tool dynamometer is attached to the tool post for force measurement. Turning operation on the work piece is performed on lathe at four different speeds, keeping the feed and depth of cut constant. Cutting forces acting on the tool, temperature at the tool and material interface are recorded. Power consumed being determined by a wattmeter and surface roughness values are measured. The same procedure is repeated for the other two work-pieces materials and optimal speeds for machining are determined for the three specimens. The results obtained are compared with the theoretical values and found to be very close.

Educating the Engineer of 2020

How will engineering practice change in the next twenty years? What are the implications to engineering education? Will we have achieved gender equity? These questions will be discussed in the context of three recent reports of the US. National Academy of Engineering – The Engineer of 2020: Global Visions of Engineering in the New Century; Educating the Engineer of 2020: Adapting Engineering Education to the New Century; and Beyond Bias and Barriers: Fulfilling the Potential of Women in Academic Science and Engineering.

A New Generation of Tools for the Design of Tall Buildings Subjected to Wind Loads

Current approaches to the estimation of wind-induced wind effects on tall buildings are based largely on 1970s and 1980s technology, and were shown to result in some cases in errors of up to 40%. Improvements are needed in: (i) the description of direction-dependent aerodynamics; (ii) the description of the direction-dependent extreme wind climate; (iii) the estimation of inertial wind effects induced by fluctuating aerodynamic forces acting on the entire building envelope; (iv) the estimation of uncertainties inherent in the wind effects; and (v) the use of applied wind forces, calculated inertial forces, and uncertainty estimates, to obtain via influence coefficients accurate and risk-consistent estimates of wind-induced internal forces or demand-to-capacity ratios for any individual structural member. Methods used in current wind engineering practice are especially deficient when the distribution of the wind loads over the building surface and their effects at levels other than the building base are not known, as is the case when measurements are obtained by the High-Frequency Force Balance method, particularly in the presence of aerodynamic interference effects due to neighboring buildings. The paper describes a procedure that makes it possible to estimate wind-induced internal forces and demand-to-capacity ratios in any individual member by: developing aerodynamic and wind climatological data sets, as well as aerodynamic/climatological directional interaction models; significantly improving the quality of the design via rigorous structural engineering methods made possible by modern computational resources; and properly accounting for knowledge uncertainties. The paper covers estimates of wind effects required for allowable stress design, wherein knowledge uncertainties pertaining to the parameters that determine the wind loading are not considered, as well as estimates required for strength design, in which these uncertainties need to be accounted for explicitly.

Experimental Study of Static Friction in a Spherical Elastic-Plastic Contact

The elastic-plastic contact between a deformable sphere and a rigid flat during pre-sliding is studied experimentally. Measurements of friction force and contact area are done in real time along with an accurate identification of the instant of sliding inception. The static friction force and relative tangential displacement are investigated over a wide range of normal preloads for several sphere materials and diameters. It is found that at low normal loads the static friction coefficient depends on the normal load in breach of the classical laws of friction. The pre-sliding displacement is found to be less than 5 percent of the contact diameter, and the interface mean shear stress at sliding inception is found to be slightly below the shear strength of the sphere material. Good correlation is found between the present experimental results and a recent theoretical model in the elastic-plastic regime of deformation.

Model-Eliciting Activities: A Research-Based Method for Inquiry Learning and Professional Development in the Engineering Classroom

Attracting students to engineering is a challenge. In addition, ABET requires that engineering graduates be able to work on multi-disciplinary teams and apply mathematics and science when solving engineering problems. One manner of integrating teamwork and engineering contexts in a first-year foundation engineering course is through the use of Model-Eliciting Activities (MEAs) — realistic, client-driven problems based on the models and modeling theoretical framework. A Model-Eliciting Activity (MEA) is a real-world client-driven problem. The solution of an MEA requires the use of one or more mathematical or engineering concepts that are unspecified by the problem — students must make new sense of their existing knowledge and understandings to formulate a generalizable mathematical model that can be used by the client to solve the given and similar problems. An MEA creates an environment in which skills beyond mathematical abilities are valued because the focus is not on the use of prescribed equations and algorithms but on the use of a broader spectrum of skills required for effective engineering problem-solving. Carefully constructed MEAs can begin to prepare students to communicate and work effectively in teams; to adopt and adapt conceptual tools; to construct, describe, and explain complex systems; and to cope with complex systems. MEAs provide a learning environment that is tailored to a more diverse population than typical engineering course experiences as they allow students with different backgrounds and values to emerge as talented, and that adapting these types of activities to engineering courses has the potential to go beyond “filling the gaps” to “opening doors” to women and underrepresented populations in engineering. Further, MEAs provide evidence of student development in regards to ABET standards. Through NSF-funded grants, multiple MEAs have been developed and implemented with a MSE-flavored nanotechnology theme. This paper will focus on the content, implementation, and student results of one of these MEAs.

Adhesive Wear of Duplex-Treated Tool and Structural Steels

Thin ceramic coatings deposited on the surface of tools and machine parts by PVD methods improve considerably their tribological properties. However these hard brittle coatings can be damaged rapidly if plastic deformation initiates in the substrate near the coating-substrate interface when subject to a relatively high load. The logical way how to treat such problems is improvement of the mechanical characteristics of subsurface layers by heat treatment or thermo-chemical treatment such as plasma nitriding. The typical duplex process involves plasma nitriding and PVD coating treatment of steels. Thickness of the nitride layers depends on the activity of nitrogen in the plasma, process temperature and time. The type and thickness of nitrides can influence considerably the quality of the deposited PVD coatings and their adhesion to a nitrided substrate. High-speed steels and Cr-V ledeburitic steels were plasma nitrided and duplex-coated (pulse plasma nitriding + PVD TiN or CrN coating) at various combinations of processing parameters. The wear resistance of the non-nitrided, PVD coated and duplex-coated steel surface was examined by ring-on-plate and plate-on-plate tribological testers. The effect of subsequent PVD–coating performed on plasma nitrided specimens can be considered as very positive when the specimens were severe loaded. The tested duplex treated low-alloy steel 31CrMoV9 was pulse plasma nitrided and then coated by different PVD coatings (TiN, CrN, TiAlN and (CrN-TiN)x3). The results of tribological tests (ring-on-plate tribometer) confirmed the high wear resistance of duplex treated steels.