Effect of nano particle size on mechanical properties

Effect of nano particle size on mechanical properties

1. Effect of Nano-particle size on Mechanical properties Presented by Maria Ashraf Muhammad Ashraf

2. Introduction Effect of Nano-particle size on Mechanical properties Elastic Modulus of Nano-material Hardness and Strength of Nano-material Fatigue and Creep of Nano-material

3. Introduction- What are nanomaterials? Nanomaterials are defined as materials in which on of the dimensions ( x , y , or z ) is in the range (length scale) of 1 – 100 nanometers ( nm m-9) The significance of decreasing grain size in order to improve the mechanical properties of a material is apparent in the production of ultrafine grain materials (UFG) which have one dimension in the order of 100-1000 nm. UFG materials are further deformed to produce nanomaterials .  

4. Effect of Nano-particles size on Mechanical properties

5. Elastic Modulus An  elastic modulus  (also known as   modulus  of  elasticity ) is a quantity that measures an object or substance's resistance to being deformed elastically (i.e., non-permanently) when a stress is applied to it.

6. Elastic modulus is of material is proportional to the bond strength between the atoms or molecules. Structure independent and dependent on temperature and defect concentration. A large increase in vacancy and other defect concentrations can be treated as equivalent to higher apparent temperature. If the temperature is increased, the mean separation between the atoms increase and modulus decreases. Thus , the nanomaterials by virtue of their high defect concentration , may have considerably lower elastic properties in comparison to bulk materials.

7. Nickel powder produced by electroplating with negligible porosity levels had an E value comparable to fully dense conventional grain size Nickel . Subsequent work on porosity-free materials has supported these conclusions, and it is now believed that the intrinsic elastic moduli of nanostructured materials are essentially the same as those for conventional grain siz materials until the grain size becomes very small, less than 5 nm.

8. Hardness and Strength strength ;-capacity of an object or substance to withstand great force or pressure Hardness  is material's resistance to any type of deformation i.e. scratching, bending , compressing etc . It is very easy to make a scratch in plastic than that of steel because steel is harder .

9. Strength and Hardness of nanostructured material increases with decreasing size Grain boundaries deformation

10. Fatigue Fatigue:- When component subjects to fluctuating or repeated load, material tend to develop characteristic behavior which is different from that under steady load. Fatigue is phenomena which lead to fracture Fracture take place under repeated or fluctuating stresses whose maximum value is less than the tensile strength of the materials(under steady load) Fatigue fracture is progressive beginning as minute crake that grow under the action of fluctuating stress

11. Fatigue failure is characterized by three stages Crack initiation Crack propagation Final fracture Addition of nano particles, results in an order of magnitude reduction in fatigue crack propagation rate for systems Fatigue crack propagation rate can be reduced by reducing the diameter and length and improving their dispersion

12. The S-N Curve A very useful way to visual the failure for a specific material is with the S-N curve. The “S-N” means stress verse cycles to failure, which when plotted using the stress amplitude on the vertical axis and the number of cycle to failure on the horizontal axis. An important characteristic to this plot as seen is the “ fatigue limit ”. Materials such as aluminium , copper and magnesium do not show a fatigue limit; therefore they will fail at any stress and number of cycles

13. Creep Creep is the time-dependent permanent deformation that occurs under stress, for most materials, it is important only under, elevated temperature When materials subjected to creep, the materials continue to deform until it’s usefulness is seriously impaired. It is both a time & temperature dependent phenomenon. Creep is probably the most widely studied long-term property

14. Effect of N ano-particles in polymers Many studies shows that the addition of nanoparticles to neat polymers can significantly improve the creep resistance of the polymers at various stress and temperature levels. During creep deformation, the molecular chains are stretched and re-oriented. Creep behavior is affected by molecular weight, degree of crystallinity , and the chemical resistance of the polymer.

15. Creep curve

16. Creep behavior on CNT nano -composite

17. small grain sizes is responsible for low strain rates and higher than expected creep resistance