The slides, written out
AI-drawn illustration. Simplified to explain the idea, not to scale.
Slide 1 · STRONG STEEL
STRONG STEEL. SMART CONNECTIONS.
MATERIAL
TOUGHNESS
&
ALUMINIUM TO STEEL
CONNECTIONS
Tests that assess toughness.
Connections that control corrosion.
KNOW THE TESTS.
BUILD WITH CONFIDENCE.
Slide 2 · HOW DO WE TEST STEEL TOUGHNESS?
HOW DO WE TEST STEEL TOUGHNESS?
THE CHARPY V NOTCH IMPACT TEST
TOUGHNESS ≠ STRENGTH
KG
STRENGTH
Ability to carry load.
TOUGHNESS
Ability to absorb energy and resist fracture, particularly under sudden impact loading.
WHY THE NOTCH?
The V notch creates a standardized stress concentration under controlled test conditions.
It allows the material's notch toughness and impact behaviour to be assessed.
KEY TAKEAWAY
Higher absorbed impact energy
→ Greater toughness
Slide 3 · THE PENDULUM TEST
THE PENDULUM TEST
HOW THE CHARPY IMPACT TEST WORKS
1
PREPARE THE SPECIMEN
A square section specimen is prepared with a V shaped notch on one face.
V-NOTCH
2
POSITION THE SPECIMEN
The specimen is supported on the anvils of the machine, with the notch facing away from the striker.
STRIKER
ANVIL
3
RELEASE THE PENDULUM
A pendulum of known mass is raised to a known height and released.
4
IMPACT & FRACTURE
The striker hits the specimen on the face opposite the notch and fractures it.
5
MEASURE ABSORBED ENERGY
The pendulum continues upward after fracture. A pointer records the height it climbs.
POINTER
BASIC PRINCIPLE
E_absorbed = E_initial − E_remaining
For an ideal pendulum:
E_absorbed = mg(h1 − h2)
Measured in Joules (J)
REMEMBER
The more energy absorbed, the tougher the material.
Slide 4 · STRONG STEEL
STRONG STEEL. SMART CONNECTIONS.
TOUGHNESS CHANGES
WITH TEMPERATURE
A steel that performs well at normal temperature can
become more susceptible to brittle fracture at low temperature.
CHARPY TESTING
Typically, a set of three specimens is tested.
Results are assessed against the applicable:
Average absorbed energy requirements
AND
Individual specimen requirements
LOW TEMPERATURE STEELS
LOW TEMPERATURE STEELS
CHARPY REQUIREMENTS
DEPEND ON
GRADE, THICKNESS
& TEST TEMPERATURE.
Lower temperature
increases the risk
of brittle fracture.
Requirements are specified by the applicable rules,
steel grade, thickness and service temperature.
WHY DOES THIS MATTER AT SEA?
Low temperatures can increase the risk of brittle fracture.
That's why the specified Charpy test temperature matters.
Slide 5 · STRONG STEEL
STRONG STEEL. SMART CONNECTIONS.
JOINING ALUMINIUM
TO STEEL IN SHIPS
Dissimilar metals need smart design to ensure strength, reliability and corrosion control.
THE TWO BIG CONCERNS
01 GALVANIC CORROSION
Aluminium is less noble than steel and acts as the anode in seawater electrolyte, leading to galvanic corrosion.
02 THERMAL EXPANSION
Aluminium has a significantly higher coefficient of thermal expansion than steel. Temperature changes create stresses at the joint.
APPROACHES FOR ALUMINIUM TO STEEL CONNECTIONS
Select the method suitable for the location, loads and service conditions.
01 INSULATED BOLTED JOINT
• Insulating gaskets, sleeves and washers electrically isolate aluminium and steel.
• This breaks the electrical circuit and helps prevent galvanic corrosion.
• Easy to assemble and allows disassembly.
02 ALUMINIUM/STEEL TRANSITION JOINT
• Explosion-bonded composite transition piece is welded to steel on one side and to aluminium on the other.
• Avoids direct fusion weld between aluminium and steel.
• Requires approved specification and control of interface temperature during welding.
03 MECHANICALLY FASTENED JOINT WITH ISOLATION
• Mechanically fastened connections can use suitable insulation between dissimilar metals.
• Reduces galvanic corrosion risk.
• Subject to structural design and classification requirements.
KEY PRINCIPLE
Isolate the metals. Manage expansion. Protect against corrosion.
STRONG CONNECTIONS. SAFE VOYAGES.
Drafted by SailR from our daily lessons. AI-drawn illustration. Simplified to explain the idea, not to scale. Last updated 19 Oct 2026.
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