Dating and random bits Flashcards

Question

What is pattern welding

Answer 1

patterns are a by product of process. Sword made from thin sheets of carburised iron – thin sheet allows a homogeneous C-content to be achieved. “Piling” / welding sheets  sword with varying properties E.g. Nydan sword 3rd century AD. Surface carburised strips could be forged together  make a layered structure with a more homogeneous C content (up to ~ 0.5%)

Answer 2

1) Medium -C core (0.5% C) 2) Backed either side with soft iron strip 0.1% C 3) Either side are 6 piled & twisted strips (0.1-0.5% C) 4) Cutting edge made from plain C-steel

Answer 3

pattern welding with finer steel strips & more of them. Suggested that it takes 25 hours to make, 128 reheats to weld pieces together

Answer 4

damascening using layers of higher C steel (contains cementite), or fragments of cast iron mixed with low-C bloom steels

Answer 5

Bars of wrought iron are packed together in furnace (c.1100) for ~ 1 week. Carbon diffused into steel  0.1% C (blister steel). Bars, cut, forged and reheated to create a more homogeneous composition (shear steel).

Answer 6

1) Carburised wrought iron, solid: low C, carburisation | 2) Decarburised cast iron, decarburisation of High C cast iron

Answer 7

Hunstman (1740) developed process where coke used as fuel (de-volatilised coal), to obtain high furnace temp. Blister steel (~0.1%C) was melted in pots with a flux, and cast to shape. As a liquid is involved, carbon pick-up from coke occurred, increasing C content of the steel

Answer 8

method for reducing C-content of liquid cast iron by blowing in air. Oxygen reacts with C in iron  CO2, lowers C-content, subsequent deoxidisation process is required to remove residual oxygen dissolved in the melt (otherwise embittle the steel)

Answer 9

Iron as Fe2O3 & Fe3O4 reduced by reaction with C, from coke; Fe203+3CO --> 2Fe +3CO2 In blast furnace at high temperature, high carbon content liquid iron. Steel has low C content (0-1.4wt %) reduce C content a lace is used to blow oxygen trough liquid steel: O2 +2C = 2CO. Liquid steel contains too much O, reduced by added element with strong preference for reaction with O: Si + O2 = SiO2 2Al + 3O2 = 2Al2O3 Deoxidisation products should float out from steel – removed with the slag, mat become trapped as inclusions. Final stages i) Degassing to remove N under vacuum ii) Removal of impurities S,P by reaction with slag iii) Alteration of composition by addition of ferroalloys Mn, Cr, Ni… iv) Stirring with Ar gas to make T & composition uniform

Answer 10

White cast iron with pearlite matrix. Subsequent annealing causes (metastable) cementite to decompose to graphite. 3 forms : • Whiteheart malleable – heating casting to 900°C in an oxidising atmosphere results in surface decarburisation. • Blackheart malleable – heating casting to 900°C in a neutral atmosphere results in decomposition of iron carbide into a graphite rosette shape, (which does not have the disadvantages of graphite flakes in cast iron). • Pearlitic malleable – heating to 900°C and then rapid quenching produces a pearlitic or martensitic matrix.

Answer 11

implicit model of the human past based upon diffusion items dated by association

Answer 12

king-list of Persia to astronomical events, (e.g., the helical rising of Sirius), however, this only extends back to about 800 BC

Answer 13

initially thought to be built by Mycenaeans - corralled roofs dated the Egyptian chronology 1500BC so must be later (giving time to sail) so around 1200BC

Answer 14

relative dating method , if object found at same archeological level as another assumed to be form the same period, older objects found below

Answer 15

absolute dating method developed in late 1940's by willard libby living organisms take up C, C-14 has half life of 5730 yrs c14 in atmosphere produced by cosmic ray neutrons interacting with n14. at point of plant death organism has same amount of c14 as in atmosphere dating by measuring amount of c14 present now and relating to amount of stable 12C by emissions of beta, or mass spectroscopy

Answer 16

because 14C content in the atmosphere is not constant past c14 data achieved from long lived trees that could be dated by counting growth rings

Answer 17

(i) . The calibration curve is not smooth, but has plateaus in it. This means applying the calibration curve results in a range of equally possible dates. (iii) . Different types of samples give different results. (iv) . Fractionation. Where different C isotopes, having different atomic masses, are processed in different ways. (v) . Reservoir effects. For example, molluscs extract carbonate dissolved in sea water, which is depleted of 14C; molluscs were a valuable contribution to the diet and are thus often radiocarbon dated, but this would make them appear older than they actually are

Answer 18

uses the 86Sr / 87Sr ratio nature of the geology influences the diet, which is expressed by measurement of the Sr isotopes in the tooth enamel of skeletons. Knowing the Sr isotope ratio one can assign a possible origin for an individual

Answer 19

trees grow I bark ring per year, can be thick or thin depending on the climate sereis has been put together dating back to 26,000 yrs ago gives precise date for wood, if the bark is still attached

Answer 20

Indentor is forced into the surface of a material, until it reaches an equilibrium depth. The diameter of the impression is then measured, and related to an arbitrary hardness scale

Answer 21

uses a steel ball indentor, the Rockwell and Vickers test use conical and pyramid-shaped indentors, respectively. The Knoop tests uses an elongated pyramid for determination of micro-hardness

Answer 22

material must plastically deform, and flow away from the moving indentor. The hardness test measures: ability of a material to elastically and plastically deform, relationships between the measured hardness of a material, and its tensile properties.

Answer 23

Materials will creep (i.e., deform) under a low load, particularly at elevated temperatures. In creep terms, elevated temperatures means at T > 0.4 Tm

Answer 24

turbine blades in jet engines. These are operated at temperatures close to their melting point, and under great stress due to the high density of the material, (a Ni-based alloy), and the centrifugal forces that consequently occur during operation

Answer 25

improved by directional solidification; this aligns columnar crystals in the direction of loading, which means that the grain boundaries are aligned parallel to the centrifugal force the blades experience

Answer 26

standard specimen is held in a furnace at the temperature of interest, (with an inert atmosphere if necessary) and its deformation recorded as in a tensile test. This gives rise to the characteristic creep curve, which shows regions of primary creep, secondary creep, and tertiary creep, leading to failure creep accelerated as usually takes place over a number of years

Answer 27

due to cyclic loading with a stress below the normal failure stress of the material

Answer 28

at defined stress amplitudes, where the stress varies from a maximum to a minimum, giving a characteristic stress amplitude; S = stress.a = (stress.max - stress.min)/2 The number of cycles to failure is recorded, which can be typically in the range of 105 to 106, and plotted on an S-N curve.

Answer 29

originate from a flaw, often a surface flaw concentration of the applied stress occurs at the tip of such a flaw; crack can initiate from this point and slowly grow across the section with each application of the cyclic load. Once CSA< an area below that which can support the applied load, the crack propagates rapidly across the section, leading to sudden failure

Answer 30

by concentric rings

Answer 31

(i) . improving the surface finish to reduce surface flaws that might act as crack initiators. (ii) . Eliminating internal defects, such as pores or inclusions, that could also act as crack initiators. (iii) .design modifications to reduce stress raisers (iv) . surface treatments (in metals) such as shot-peening or carburising, which will impart compressive residual stresses to the surface and reduce surface-related crack initiation.

Answer 32

A standard specimen is placed in a fixture, and a weighted arm released to swing down and impact on the specimen. The specimen is notched to ensure its fracture, and the height to which the arm reaches, after passing the specimen, is used as a measure of the energy absorbed by fracturing the specimen

Answer 33

ductile-brittle transition caries with steel composition, generally around -30oC to -50oC

Answer 34

use at low temperatures sinking of the liberty ships in WW2 because of the welded construction, and in the sinking of the titanic