News Update on Material Engineering : Dec 2020

Tissue Engineering of Bone: Material and Matrix Considerations

When the normal physiologic reaction to fracture does not occur, such as in fracture nonunions or large-scale traumatic bone injury, surgical intervention is warranted. Autografts and allografts represent current strategies for surgical intervention and subsequent bone repair, but each possesses limitations, such as donor-site morbidity with the use of autograft and the risk of disease transmission with the use of allograft. Synthetic bone-graft substitutes, developed in an effort to overcome the inherent limitations of autograft and allograft, represent an alternative strategy. These synthetic graft substitutes, or matrices, are formed from a variety of materials, including natural and synthetic polymers, ceramics, and composites, that are designed to mimic the three-dimensional characteristics of autograft tissue while maintaining viable cell populations. [1]

Bulk amorphous metal—An emerging engineering material

During the last two decades, researchers have developed families of metal alloys that exhibit exceptional resistance to crystallization in the undercooled liquid state. Upon cooling, these alloys readily form glass or vitrify to form bulk amorphous alloys or bulk metallic glasses. The stability of the undercooled molten alloys with respect to crystallization has enabled studies of liquid thermodynamics, rheology, atomic diffusion, and the glass transition previously not possible in metallic systems. Bulk amorphous alloys exhibit very high strength, specific strength, and elastic strain limit, along with unusual combinations of other engineering properties. These factors, taken together, suggest that bulk amorphous metals will become widely used engineering materials during the next decade. [2]

Silkworm silk as an engineering material

While silk exhibits high values of tensile strength and stiffness, these properties are compromised by their poor reproducibility. We present the results of experiments aimed at characterizing the variability of tensile properties exhibited by cocoon silk from Bombyx mori silkworms. Scanning electron microscopy is used to measure an average diameter for individual test specimens; the interspecimen variability of diameter is quantified and found to be inadequately represented by standard deviation. When load‐extension data are converted into stress‐strain curves, a marked improvement in reproducibility is realized if each specimen cross‐section is calculated from diameter measurements specific to that specimen. Nevertheless, a significant variability in fracture stress remains; a Weibull analysis reveals that silkworm silk has a failure predictability comparable with that of glass and nonengineering ceramics. Unloading/reloading tests demonstrate that stiffness is not significantly affected by cumulative deformation, and the stress–strain relationship is not sensitive to strain rate. [3]

Assessment of Strength Characteristics of Concrete Made from Locally Sourced Gravel Aggregate from South-South Nigeria

Aims: The aim of this research is to verify the suitability of local gravel aggregates obtained from the Southern part of Akwa Ibom State for designed concrete production in place of crushed granite aggregate sourced from distance places at exorbitant cost. This paper assesses the strength characteristics of concrete made from two locally sourced gravel aggregates of 10 mm and 20 mm maximum sizes.

Study Design: Three samples of gravels divided into washed and unwashed gravels were used for the research. Concrete mix design of 25 N/mm2 at 28 days of curing was the target mean strength of the research.

Place and Duration of Study: Department of Civil Engineering, Covenant University, Ota –Nigeria, between September 2014 and July 2015.

Methodology: Particle size distribution test, specific gravity test, water absorption test, aggregate crushing value test, flakiness and elongation tests, slump test, compressive strength test were performed on the samples. Concrete cubes150 mm were cast for each gravel size and three specimen tested for 3, 7, 14, 21 and 28 days compressive strength.

Results: The washed gravels with 10 mm and 20 mm maximum size reached the target mean strength with 29.7 N/mm2 and 26.2 N/mm2 respectively while the unwashed gravel with 20 mm maximum size yielded a compressive strength of 24.5 N/mm2 at 28 days.

Conclusion: The results prove that the size, grading, internal bonding and deleterious material contribute immensely to the strength of concrete made from gravel aggregate. [4]

Material Selection for Axial Spring in a Prototype Cam-Follower Mechanism

A prototype cam-follower mechanism was designed and assembled using Pro-Engineer (Pro-E) software. The mechanism is meant for application in a forth-and-back Mode II Operation of a tribotester rig. The mechanism was dynamically simulated in Pro-E to ascertain the dynamic loading status of integral parts. CES EduPack software was applied to select the best material for the spring using the Function-Objectives-Constraints approach. Candidate materials were first screened using design constraints after which shortlisted materials were ranked using design objectives. The final material choice made with reasonable trade-offs was found suitable for intended service environment requirements. [5]

Reference

[1] Khan, Y., Yaszemski, M.J., Mikos, A.G. and Laurencin, C.T., 2008. Tissue engineering of bone: material and matrix considerations. Jbjs, 90(Supplement_1), pp.36-42.

[2] Johnson, W.L., 2002. Bulk amorphous metal—An emerging engineering material. Jom, 54(3), pp.40-43.

[3] Pérez‐Rigueiro, J., Viney, C., Llorca, J. and Elices, M., 1998. Silkworm silk as an engineering material. Journal of Applied Polymer Science, 70(12), pp.2439-2447.

[4] Bamigboye, G., Ede, A., Umana, U., Odewumi, T. and Olowu, O. (2015) “Assessment of Strength Characteristics of Concrete Made from Locally Sourced Gravel Aggregate from South-South Nigeria”, Current Journal of Applied Science and Technology, 12(5), pp. 1-10. doi: 10.9734/BJAST/2016/20365.

[5] Akinluwade, K., Ogwu, G. E., Badamasi, O. T., Taiwo, A. T., Adetunji, A. R. and Adewoye, O. O. (2014) “Material Selection for Axial Spring in a Prototype Cam-Follower Mechanism”, Current Journal of Applied Science and Technology, 4(22), pp. 3134-3142. doi: 10.9734/BJAST/2014/10594.

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