In the figure, the load P = 1 N, length L = 1 m, Young’s modulus E = 70 GPa, and the cross-section of the links is a square with dimension 10 mm $$ \times $$ 10 mm. All joints are pin joints.

The stress (in Pa) in the link AB is _______.

$$(Indicate\,\,compressive\,\,stress\,\,by\,\,a\,\,negative\,$$
$$\,sign\,\,and\,\,tensile\,\,stress\,\,by\,\,a\,\,positive\,\,sign)$$

A horizontal bar with a constant cross-section is subjected to loading as shown in the figure. The Young’s modules for the sections AB and BC are 3E and E, respectively.
For the deflection at C to be zero, the ratio P/F is ________.

A hypothetical engineering stress-strain curve shown in the figure has three straight lines PQ, QR, RS with coordinates P(0,0), Q(0.2,100), R(0.6,140) and S(0.8,130). 'Q' is the yield point, 'R' is the UTS point and 'S' the fracture point.

The tougness of the material (in MJ/m³) is __________.

A $$200$$ mm long, stress free rod at room temperature is held between two immovable rigid walls. The temperature of the rod is uniformly raised by $$250$$^oC. If the Young's modulus and coefficient of thermal expansion are $$200$$ GPa and $$1 \times {10^{ - 5}}/{}^ \circ C,$$ respectively, the magnitude of the longitudinal stress (in MPa) developed in the rod is _________