C18 vs C40

C40 is 1.6 times as stiff as C18. It is 1.3 times as dense. Per unit mass C40 is 1.2 times as stiff. Strength: f_m,k = 18 MPa for C18, f_m,k = 40 MPa for C40.

C18 EN 338:2016 C40 EN 338:2016

Side by side

ratio = C40 / C18 · log scale

Property	C18	C40	Unit	Ratio
E₁ Modulus, direction 1	9	14	GPa	1.56×
E₂ Modulus, direction 2	0.3	0.47	GPa	1.57×
E₃ Modulus, direction 3	0.3	0.47	GPa	1.57×
G₁₂ Shear modulus 1-2	0.56	0.88	GPa	1.57×
G₁₃ Shear modulus 1-3	0.56	0.88	GPa	1.57×
E₀,₀₅ Modulus parallel to grain, 5 % fractile	6	9.4	GPa	1.57×
ρ Density	380	480	kg/m³	1.26×
ρ_k Density, characteristic (5 % fractile)	320	400	kg/m³	1.25×
f_m,k Bending strength	18	40	MPa	2.22×
f_t,0,k Tension parallel to grain	10	26	MPa	2.6×
f_t,90,k Tension perpendicular to grain	0.4	0.4	MPa	1×
f_c,0,k Compression parallel to grain	18	27	MPa	1.5×
f_c,90,k Compression perpendicular to grain	2.2	2.8	MPa	1.27×
f_v,k Shear strength	3.4	4	MPa	1.18×
E/ρ Specific stiffness E/ρ · derived	23.68	29.17	MJ/kg	1.23×
c₀ Bar wave speed √(E/ρ) · derived	4867	5401	m/s	1.11×
f/ρ Specific strength f/ρ · derived	47.37	83.33	kJ/kg	1.76×

Values at the first thickness band or product form of each material (EN 338:2016; EN 338:2016). A minimum and a characteristic value are not the same kind of number — read the ratio as a guide. Each material's page lists every band and every source.