Summary
Highlights
The video introduces the tensile test according to DIN EN ISO 6892, showcasing the testing machine and monitor setup. It highlights different tensile test specimen shapes, including flat, round cylindrical, and shorter cylindrical rods.
The first test is performed on a material with a defined yield strength. The process involves marking the original length (l0) and measuring the original diameter (d0) to calculate the original cross-sectional area (s0). The specimen is then secured in the testing machine, and an extensometer is attached for precise extension measurement.
The stress-strain curve for a material with defined yield strength is explained. It begins with a linear elasticity stage (Hooke's law), followed by the yielding region (flow region), and then the strain hardening range, culminating in the ultimate tensile strength (UTS or rm). Necking occurs after UTS, leading to fracture.
After fracture, the specimen shows a cone-cup fracture. The stress-strain diagram is further detailed, highlighting the upper yield strength (reh), lower yield strength (rel), and ultimate tensile strength (rm) with their corresponding formulas. Strains at ultimate tensile strength (ag, agt) and fracture (a, at) are also discussed.
The second test is conducted on a material without a distinct yield point. The setup and initial measurements are similar to the first test. The accompanying stress-strain diagram shows the basic physical quantities of force and elongation.
For materials without a yield point, Young's modulus is determined from the initial straight line's slope. Strain hardening leads to maximum tensile strength, followed by necking and ultimately shear fracture, characterized by a fracture surface at below 45 degrees to the loading axis.
Since there's no distinct yield strength, the 0.2% proof stress (Rp0.2) is used as a substitute, calculated by a parallel offset at 0.2% strain. The video then demonstrates manually determining the elongation after fracture (Lu) and the diameter after fracture (Du) to calculate the percentage reduction of area.
A direct comparison of the two stress-strain curves reveals clear differences: the first curve shows a pronounced yielding region, while the second directly transitions to strain hardening. Differences in ultimate tensile strengths, elongations to fracture, and a significant difference in Young's modulus (a 3:1 ratio) are observed.