**5. Modern experimental approaches**

Laboratory-scale tensile and torsion testing machines allow experimental evaluations between any applied tensile/torque loads and the induced linear elongations or twist on composite specimens with natural fibers. In engineering terms, they facilitate the experimental evaluation of yield strength, Young modulus *E* or shear modulus *G* with accuracy. The specimen can also be brought to the point of destruction and such experiments allow the establishment of the failure point of the material.

Such experiments can be performed with the required precision on SM1002 Bench-Top Tensile Testing Machines and SM1001 Torsion Testing Machines from Tecquipment. The experimental evaluation of Poisson's Ratio with the relationship *ν* ¼ �*dεt=dε<sup>a</sup>* performed under EU Standard 10,002–1 directions is also important because it provides input parameters for simulations.

If the fibers are randomly oriented in the matrix may be acceptable to consider the composite a homogenous, isotropic linear elastic material. Under such

**Figure 11.** *3D CAD model of tensile testing machine.*

**Figure 12.** *3D CAD model of a torsion testing machine.*

assumptions, the elastic properties of the composite material are fully defined by the Young modulus and shear modulus and the formula involving them allows the calculation of Poisson ratio *ν*:

$$G = \frac{E}{2(1+\nu)}, \nu = \frac{E}{2G} - 1\tag{8}$$

The following pages briefly introduce 3D CAD models of tensile testing, torsion, creep and rotating fatigue computer controlled machine recommended in the experimental research of composite materials with natural fibers – see **Figures 11**–**14**. Screenshots of specific tests are also introduced in **Figures 15**–**18**.

**Figure 13.** *3D CAD model of a creep testing apparatus.*

**Figure 14.** *3D CAD model of a rotating fatigue machine.*
