Abu N M Faruk

Prediction of Micro and Nano Indentation Size Effects from Spherical Indenters

In the present work, a micromechanical model based on dislocation mechanics for predicting indentation size effect from spherical indenters is developed and compared with the most widely used Swadener et al. (2002) model. The key idea proposed here while deriving the model is that a nonlinear coupling between the geometrically necessary dislocations (GNDs) and the statistically necessary dislocations (SSDs) can largely correct the deviation of the Swadener et al. models prediction from hardness results for small diameter indents. Furthermore, the model can be used in identifying the material length scale from micro- and nano-indentation data.

Dislocation-based model for predicting size-scale effects on the micro and nano indentation hardness of metallic materials

In micro- and nano-indentation tests for evaluating strength and stiffness properties of engineering materials, a commonly observed phenomenon is the dependence of material properties on the indent size, also known as indentation size effect (ISE). The objective of the present work is to formulate a micro-mechanical based model based on dislocation mechanics for predicting ISE from conical or pyramidal (Berkovich and Vickers) indenters and to compare it with the most widely used Nix-Gao model. The key idea proposed here while deriving the model is a non-linear coupling between the geometrically necessary dislocations (GNDs) and the statistically stored dislocations (SSDs) that eventually allows it to simultaneously predict ISE from both micro- and nano-indentations tests on a wide range of metallic materials while the Nix-Gao model fails to do so. The work also presents a method for identifying the length scale parameter from micro- and nano-indentation experiments and also correlates it with the spacing between dislocations and thus gives a physical interpretation of the material intrinsic length scale.

Application of Nano-Technology in Pavement Engineering: A Literature Review

Nanotechnology is the term used to cover the design, construction, and utilization of structures with at least one dimension measured in nanometers. Initially developed in the fields of physics and chemistry, nanotechnology has established itself as an inter-disciplinary science. However, for the technology to have practical effect in the advancement of humanity, it needs to be applied in areas such as the engineering fields. This paper focuses specifically on current and potential developments in the field of pavement engineering where the unique properties of nanomaterials may be used for the betterment of this field, based on identified needs and challenges in pavement engineering. It is demonstrated that there are several areas where nanotechnology can complement pavement engineering, first, through the development of improved materials to be used in pavement constructions and second, through the use of characterization methods to improve the understanding of the materials. Examples of current and planned research in these areas are cited and discussed. Finally, current challenges in exploiting the unique properties of nanomaterials in pavement engineering are indicated and discussed.

Theoretical Review of Different Asphalt Mix-Design Methods and their Applicability for Developing Countries like Zambia

Asphalt pavements in Zambia have been experiencing premature failures due to distresses such as rutting, fatigue cracking, bleeding, moisture damage, and pot-holing. Most of these failures have been accusingly attributed to poor workmanship of Contractors who fail to adhere to specifications. Literature has, however, revealed that the materials used and the mix-design methods adapted also have a significant effect on the long-term performance of these asphalt pavements. To mitigate for these effects, some developed countries have developed new approaches like Superpave and Balanced Mix Design (BMD) methods that are performance-based, for the design of Hot Mix Asphalt (HMA) with the primary objective of improving the performance of asphalt pavements. By contrast, Zambia, like most developing countries, still uses the empirical Marshall Stability method that has inherent challenges in satisfactorily addressing the above mentioned pavement failures. This paper presents a theoretical review of the material types and mix-design methods currently used in Zambia to verify if premature failures of pavements can be attributed to the materials used and/or the mix-design methods adapted. Different mix-design methods and their characteristic attributes were comparatively reviewed to assess their potential applicability for use in a developing tropical country like Zambia.

Search for a Practical Laboratory Cracking Test for Evaluating Bituminous (HMA) Mixes

As an effort toward developing a simple and practical laboratory cracking test method that can be used routinely, on a daily basis, to optimize Hot-Mix Asphalt (HMA) designs, various monotonic loading single shot cracking tests were comparatively evaluated in the laboratory alongside the repeated (dynamic) loading Overlay Tester (OT R ) test. These monotonic crack tests included the Indirect Tension (IDT) test, Semi-Circular Bending (SCB), Overlay Tester in a monotonic loading mode (OT M ), and Disc-Shaped Compact Tension Test (DSCTT). The research methodology entailed characterizing the cracking resistance potential of various commonly used Texas HMA mixes of known field cracking performance, with different mix-design variables. The corresponding findings indicated that while the monotonic loading tests, particularly the OT M and IDT are much simpler, more practical and more repeatable with lower variability in the test results, the dynamic loading OT R test, where both crack initiation and propagation phases are sufficiently accounted for, exhibited superior screening capabilities in terms of the HMA cracking resistance potential and sensitivity to mix-design variables such as the asphalt-binder content and temperature variations. Overall, the results indicated that both the IDT and OT M could potentially serve as routine surrogate and/or supplementary crack tests to the OTR, subject to field validation.