1. Properties of materials

2. The behaviour of a given material is characterised by the response to a stimulus. Mechanical properties (behaviour under a set of forces) Physical properties (behaviour under action of temperature, electrical or magnetic fields or radiation) Chemical properties (behaviour under the action of chemicals)

3. Mechanical properties studied as: time –independent time-dependent temperature-dependent

4. Applying a force to a structure causes a stress bringing about a strain. STRESS or TENSION  : the ration between force F and the surface A to which is applied (Nm -2 o Pa).  = F/A Three main types of stress: TENSILE, COMPRESSION and SHEAR

7. ELASTIC If, once removed the applied force, the material gains the initial state, such behavior is said to be ELASTIC

8. linear elastic behavior non linear elastic behavior (rubber) Anelastic behavior E elastic Hysteresis

9. LINEAR All materials, for small stresses, show a LINEAR elastic behavior (Hooke’s law) σ = E ε E = elastic modulus (Young modulus, dimensions of a pressure)

10. Curiously, the cause (load) is on the abscissa scale)

12. Covalent or ionic solids Metals Polymers E T melt

14. Tensile measurements: fragile (brittle) materials break beyond the elastic limit (ceramics, glasses) ductile materials (metals, polymers): plastic deformation

15. Fragile Material Ductile material

19. Toughness Toughness measures the energy a material can store before breaking Area under the curve!

20. Indeed, a corrected curve should be used… striction

21. Another measure of the cohesive strength of the material: tenacity Charpy pendulum

23. Time dependent mechanical properties: Creep Fatigue

24. CREEP A constant static load may cause deformation Not so important at ambient temperature, i.e. with biomaterials Relevant process when T > 0,3-0,4T melt (Metals and ceramics) T > T g (Polymers and glasses)

26. FATIGUE Degration in mechanical properties when a material is subjected to cyclic stresses Samples are subjected to different loads, and the number of cycles cause breakdown is measured at each load

27. Often, a limit value for the load (FATIGUE LIMIT) is observed

28. HARDNESS Property of the external layers of a material: resistance to scratching (Mohs’ scale), to abrasion and to plastic deformation upon compression. Measure: i) formation of an indentation by applying a static constant load for a definite time; ii) evaluation of the dimension

29. Rockwell Method

31. Ultimate Tensile strength Relationship between hardness and UTS

32. THERMAL PROPERTIES OF MATERIALS

33. Thermal capacity* Thermal expansion* Thermal c onductivity Resistance to t hermal shocks* * Not really important in biomaterials

34. THERMAL CAPACITY Attitude of a body to store heat Ratio between exchanged heat and change in temperature SPECIFIC HEAT When normalised to unit mass  SPECIFIC HEAT

35. THERMAL CONDUCTIVITY Attitude of a body to transfer heat The thermal conductivity coefficient is defined through Fourier’s law: the heat flux across a unit surface is proportional to the temperature gradient (with inverted sign)

36. THERMAL EXPANSION Usually all solids expand when heated Coefficient of linear thermal expansion ()=

38. Chemical characterization Often surface only

40. Others: HRTEM Adsorption (porous systems)

41. Contact angle: Measures the wettability of a surface by a liquid Usually water or aqueous solutions (hydrophobicity/hydrophilicity) Also the surface tension of the solid

42.   lv  sl  sv BIOGLASS SILANIZED

43. Ways of measuring contact angles

44. ESCA Highly energetic X-rays cause expulsion of the electrons of the inner cores, which have different binding energies, so allowing chemical determination

47. Infrared Spectroscopy: functional groups in a molecule are recognized through their vibrational features A well developed technique, very powerful…

48. Versions of the technique for surface analysis

49. Scanning tunneling microscope

51. The end