The tensile strength of pure titanium is 265-353 MPa, and that of general titanium alloy is 686-1176 MPa, up to 1764 MPa at present. Titanium alloys have the same strength as many steels, but much better strength than titanium alloys. Here, specific strength refers to the strength of a material divided by its apparent density, also known as strength-weight ratio. The international unit of specific strength is (N/m2)/(kg/m3) or N.m/kg. The ratio of tensile strength to apparent density of materials is called specific strength. The ratio of strength (tension) to density at fracture point. The compressive strength of titanium and its alloys is not lower than their tensile strength. The compressive yield strength and tensile yield strength of industrial pure titanium are approximately equal, while the compressive strength of Ti-6Al-4V and Ti-5Al-2.5Sn alloys is slightly higher than the tensile strength. The shear strength is generally 60%-70% of the tensile strength. The compressive yield strength of titanium and titanium alloy sheets is 1.2-2.0 times of the tensile strength. In normal atmosphere, the rupture strength of processed and annealed titanium and titanium alloys is (0.5-0.65) times the tensile strength. The durable strength of annealed Ti-6Al-4V was 0.2 times of tensile strength when 107 fatigue tests were carried out in notch state (Kt=3.9). The hardness of the highest purity processed industrial pure titanium is usually less than 120HB, while the hardness of other purity processed titanium is 200-295HB. The hardness of pure titanium castings is 200-220 HB. The hardness of titanium alloy under annealing is 32-38HRC, which is equivalent to 298-349HB. The hardness of as-cast Ti-5Al-2.5Sn and Ti-6Al-4V alloys is 320HB, and that of low gap impurity Ti-6Al-4V castings is 310HB. Tensile elastic modulus of industrial pure titanium is 105-109 GPa, and that of most titanium alloys is 110-120 GPa under return condition. Age hardening titanium alloy has a slightly higher tensile modulus than annealed titanium alloy, and the compressive modulus is equal to or greater than the tensile modulus. Although the stiffness of titanium and titanium alloys is much higher than that of aluminium and aluminium alloys, it is only 55% of that of iron. The specific modulus of elasticity of titanium alloys is the same as that of aluminium alloys, which is second only to beryllium, molybdenum and some superalloys. The torsional or shear modulus of industrial pure titanium is 46 GPa, and the shear modulus of titanium alloy is 43-51 GPa. In order to improve the strength of titanium alloy and increase the content of interstitial elements, the impact resistance and fracture toughness of the alloy will be harmful. According to the different types and states of titanium alloys, the impact strength of Charles notch of industrial pure titanium is 15-54J/cm2, and the casting state is 4-10J/cm2. The impact strength of titanium alloy under annealing is 13-25.8J/cm2, and the aging state is slightly lower. The impact strength of Cast Ti-5Al-2.5Sn alloy with V-notch is 10J/cm2, and that of Ti-6Al-4V alloy is 20-23J/cm2. The lower the oxygen content is, the higher the value is. Many titanium alloys have high fracture toughness, or good crack propagation resistance. The annealed Ti-6Al-4V alloy is a kind of material with excellent toughness. When notch concentration factor Kt = 25.4mm, the ratio of notch tensile strength to non-notch tensile strength is greater than 1. Titanium alloys can also maintain certain properties at high temperatures. General industrial titanium alloys can maintain their useful properties at 540 C, but they can only be used for a short time. The temperature range for a long time is 450 – 480 C. Titanium alloys for use at 600 C have been developed. Titanium alloys can be used as missile materials for a long time at 540 C and for a short time at 760 C. Titanium and titanium alloys can maintain their original mechanical properties at low and ultra-low temperatures. With the decrease of temperature, the strength and ductility of titanium and titanium alloys increase gradually. Many annealed titanium alloys have sufficient ductility and fracture toughness at – 195.5 C. Ti-5Al-2.5Sn alloy with very few interstitial elements can be used at – 252.7 C. The ratio of notched tensile strength to non-notched tensile strength is 0.95-1.15 at – 25.7 C. Liquid oxygen, liquid hydrogen and liquid fluorine are important propellants for missiles and cosmic devices. The low temperature properties of materials used to make cryogenic gas containers and cryogenic structures are very important. The ductility of titanium alloy is still above 5% when the microstructure is equiaxed and the content of interstitial elements (oxygen, nitrogen, hydrogen, etc.) is very low. Most titanium alloys have poor ductility at – 252.7 C, while the elongation of Ti-6Al-4V alloys can reach 12%.