EVIDENCE FILE 2 :
Waiting for a Grainy Day
Next , we need to search for clues in the steel ’ s microstructure . To our eyes , metals look shiny and uniform , but under a microscope we can see they are actually made of lots of connected pieces , called grains . The smaller these grains , the stronger the steel . The microstructure may also show us inclusions – these are sneaky blobs of non-metal atoms that clump up between grains . Inclusions make metals weaker , but they can be avoided by reducing the amount of tramp elements . What do you notice about the microstructures in Evidence # 02 ?
EVIDENCE ID : 4QU1L4- # 02
= grain
STEEL AT 200X MAGNIFICATION = inclusion
FUN FACT TRUMPET When it comes to materials , being strong and being tough are two different things ! Strong materials are difficult to deform , and tough materials are difficult to fracture . For example , glass has high strength but poor toughness , while rubber has low strength and very good toughness .
EVIDENCE FILE 3 :
When metals reach their limit , they break in either a brittle or a ductile way , depending on their temperature . Brittle fracture is clean , quick and sudden , like snapping spaghetti . It leaves a flat surface behind . Ductile fracture is slower ; the metal changes shape and it might not break all the way through because it stretches , like pulling apart slime . Metallurgists prefer ductile fracture because that means more energy is needed to break the metal , but engineers of 1912 didn ’ t have a good way to test for this energy . The temperature of the water was -2 ° C when the iceberg struck – at this temperature , was the Titanic tough ? Or did it break easily ?
EVIDENCE ID : 4QU1L4- # 03
FUN FACT TRUMPET Take a tin of beans and lift it one metre in the air . You ’ ve just exerted 4 joules of energy : if you put all that energy into a single millisecond , that ’ s how much energy it took to fracture the Titanic hull at -2 ° C . Yikes !
Reaching Breaking Point
SAMPLES AFTER FRACTURING AT ICY WATER TEMPERATURE
Sample __________________ has smaller grains than sample __________________
AWESOME
ACTIVITIES ALERT
The sample with the most inclusions is
__________________ The sample that broke in a brittle way is :
_____________________________________________
The sample that broke in a ductile way is :
_____________________________________________
Words : Bee Rich . Illustration : Yulia Sirotina
SCAN ME
OK , detective , now you ’ ve reviewed all the evidence it ’ s time to arrive at your final verdict . Did Titanic ’ s steel fall short ? The good news is metallurgy knowledge has improved a lot in the last 100 years , making today ’ s ships safer than ever . CASE CLOSED !
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