Tensile testing machine , said machine comprising: - a frame provided with a first fastening element at a first end of a test specimen whose elongation is to be measured along a tensile axis (X1), - tensile means adapted to exert a traction along the tensile axis (X1) and provided with a second fastening element , forming an axial bar, at a second end of the specimen , coaxially to the tensile axis (X1), - a first sliding plate slidably mounted along the second fastening element and on which a first part of elongation measuring means for measurements of said elongation parallel to the tensile axis (X1) is mounted, - a second intermediate plate , which is fixed to the second fastening element and to which a first guide rod is fixed, the first guide rod extending parallel to the tensile axis (X1) and passing freely through the first sliding plate , - a third sliding plate , which is slidably mounted along the second fastening element and to which a second part of the elongation measuring means is fixed, - first and second deflection rods , adapted to sense the first and second fastening elements , respectively, the second deflection rod passing through the first sliding plate and coming to bear against the third sliding plate , to act on it parallel to the tensile axis (X1), so that the elongation measuring means can detect, parallel to said axis (X1), a displacement between the first and third sliding plates , the tensile testing machine characterised in that : - the tensile testing machine further comprises -- an elastic return means returning the first and third sliding plates towards each other axially, -- a second guide rod parallel to the first guide rod , which freely guides the first and third sliding plates axially, by being disposed at their level, and - the first deflection rod is fixed with the first sliding plate through which the second deflection rod passes. - a frame provided with a first fastening element at a first end of a test specimen whose elongation is to be measured along a tensile axis (X1), - tensile means adapted to exert a traction along the tensile axis (X1) and provided with a second fastening element , forming an axial bar, at a second end of the specimen , coaxially to the tensile axis (X1), - a first sliding plate slidably mounted along the second fastening element and on which a first part of elongation measuring means for measurements of said elongation parallel to the tensile axis (X1) is mounted, - a second intermediate plate , which is fixed to the second fastening element and to which a first guide rod is fixed, the first guide rod extending parallel to the tensile axis (X1) and passing freely through the first sliding plate , - a third sliding plate , which is slidably mounted along the second fastening element and to which a second part of the elongation measuring means is fixed, - first and second deflection rods , adapted to sense the first and second fastening elements , respectively, the second deflection rod passing through the first sliding plate and coming to bear against the third sliding plate , to act on it parallel to the tensile axis (X1), so that the elongation measuring means can detect, parallel to said axis (X1), a displacement between the first and third sliding plates , - the tensile testing machine further comprises -- an elastic return means returning the first and third sliding plates towards each other axially, -- a second guide rod parallel to the first guide rod , which freely guides the first and third sliding plates axially, by being disposed at their level, and -- an elastic return means returning the first and third sliding plates towards each other axially, -- a second guide rod parallel to the first guide rod , which freely guides the first and third sliding plates axially, by being disposed at their level, and - the first deflection rod is fixed with the first sliding plate through which the second deflection rod passes. <EOS>