Question

5. Explain why the stress-strain behaviors of metals measured in a tensile test cannot fully describe true stress-strain behaviors of materials. 6. Why the three point bending test is used to measure the mechanical properties of ceramics? Will the mechanical properties of ceramics be geometry dependent? 7. What is the crystallinity of polymer materials? How this structure gives rise to the unique mechanical properties of polymers? 8. For fibre-reinforced composites, will the material get totally failure after the fracture strain of the fibre phase? 9. Can you differentiate intrinsic and extrinsic semiconductors? What is the main difference between p-type and n-type semiconductors? 10. In our magnetic materials section, we introduced five different types of magnetisms. As an engineer, if you need to use the magnetic functions of materials, justify what type(s) of materials (among these five categories) will be more suitable.

Answer 1

of 5) Ans] The stoems - strain beħaviors metoly measured in a tensile test Cannot fully describe true stoom-strain behaviors of materials because Before doing the tension test, we have to determine the length and diameter of the specimen and we axume there por ometers remain Constant through-out the whole expeaiment. when we concalore the stress + so

necking which takes place who lever i o(atrem) = }(dona) area by the formula : 7 Alcrom-section ☆ Here, we actually colcalore the strenes ( corresponding to differene storing for the given Vakie of diameter which we have colculated in the beginning of expeзi ment • FRese 4tve Srp or coff № 4 such Engineering stress. But, when we do the exposiment he obseare a phenomenon called hecking and till now, we have neglecting any Bye to this, the cross-section specimen has changed as the experiment get the strenses you will be different from the ones we got when we assumed the cross-section อาวา ฉาก ains Constanta proceed further we will

6) ns) Three bajnt bendi); text is used to measure the mechanical properties of ceromics because + Jt poovides volue for the modulug of plasticity in bending, fpe xur of Atren, flexural strain and flexurof-strain response of the materror. + Olt It also gives the advantage of eve of specimen preparation and testing The mechanical properties of a ceromic materiaf affect how it befioveg as it is loaded and is dependent on both the geometru of the specimen and as well as the materially elastic modulus.

strength modulus but reduces its toughney brittle, which increases the mechanical ) Crystallinity of polymer morsing is the norongement of sofy in a well mannered behavicas. when we increase the crystreline our pofymes will become more pohore, gt also in crentes its tremicop desistant ma meeting temperature because with increase in its regularity, will be hard for any sorrent to diffure in it and for heat it to break all the bonds which will increase the temperature. o This stoucture give rise to the umiopio mec # omicaБоре *** * Potymmer because ; + aj Cage you inity in polymer is gevering by the extent of chain ordering or chain folding. If the side gacups of the poty mes backbone are large and chain morement and forsing fienry's །

short fibes do not fracture. Instead to chain secondary bonding there is an is hindered, which reduces the poobability moking mater of forming crysta line domaing In Continuation of the above chain that are arranged in an ordered manner con pack together more officiently which leads to increased crystallmity * Both inter and intra-molecular hydrogen bonding lotny important role in porymer Coyrenmoinning with increased efroin increase in crystallinity of the postymer the olenior stronges. 8) for fibre-reinforced composite, failure mec hanism in fiber composites A funсtоn оf mоn bоzото №8 such as constituent poopostios, lamination geometry istate of strey During Composite facture the ove pulled out of the metrix The work emocrapa with frihet pupp - cus provides an added component to the fracture are etci thegove

D od cling Zoivalent of Work and fins a greare contribute to toughnes. g) Difference between Intrinsic and Extrinsic semiconductor Intrinsic Extrinsic Semicon- Semiconductor ductos It is in pure It is formed by from pentovalent im punity to a pure semiconducten 2) Holes and election He of equal Number of holes are more in p-type and number of free electrons Fermi level lies are more in n-type in bo tween Valence 1 Fermi leves and conduction band dies near valence free ар bond in p-type and nego conduction hand in n-type 4) Roto of majenty and minority courtesy Roto of majority and minority Carriers anity is not unity

3 Difference between p-type and Al- type semiconductor P-type nla type semiconducten semi-conducto » Donor importing Accepto importing are used ore used 2) Taivolent importing Den ovalent importing ove are used Holes are Electrons are generared 11 Fed 4) Holes are 5) Electrons are majority Cossiers I mojority cossiers 10) Anal Five different types of Magnetism are: - al featomagnetism 6) fe & งา) 957et) c vos eኣቅዕ 7 9ካe tam as poromagnetism e) Diamagnetim

୧୧୪ use от engine- if you need to the magnetic function of materiale We preferred Fesvomogne tim materiale Joon and Micked) which can retain their magnetic propesties When the magnetic field is removed (such as Joon and