This research gives an overview of an investigation into existing non-destructive testing (NDT) methods used to analyse composite materials. From the investigation and subsequent experimentation a new technique of failure identification in composite materials was developed. The new technique is a form of thermography whereby a temperature rise in a composite material during failure is detected via a thermal camera and a thermal image captured. By observing the thermal images captured of the event the location and the severity of the failure could be gained by only using the thermal images combined with a visual inspection to validate the results. By taking a thermal image and analysing the constituent red, green and blue colours that make up the image, the location of the defect could be pinpointed. This analysis method was developed using MATLAB® in order for the location of a defect to be found using only a thermal image of the composite during failure. The analysis showed that the information that yields the most accurate location of failure was the red part of the images.
Understanding mechanical properties of healthy and unhealthy cerebral vessels is a key element in the development of their science and the relevant clinical diagnosis, prevention and treatment. Thirteen healthy samples were obtained from 23 middle cerebral arteries. The changes of force and deformation until the vessel rupture were recorded using a biaxial device. Thereafter, the stress-strain curve was plotted and fitted with a hyperelastic five-parameter Mooney-Rivlin model and the model parameters (C1, C2, C3, C4, and C5) were determined according to the best fit. For statistical comparison, the samples were divided into three age and two gender groups and subjected to non-parametric statistical analyses. Comparison of obtained results for different age groups showed that there is a significant difference between the "old" group and the other two groups (middle-aged and young). There was no significant difference between male and female groups. Therefore, the results demonstrate the changes of blood vessel wall properties with aging. The results also depicted that the arterial wall is stiffer in the circumferential direction than the axial direction. Anisotropy of cerebral vessels was confirmed by all of the tests. Therefore, the significance of the biaxial tests is in the spot light in the derived data. Moreover, good fitting of data illuminated that the use of multiple-parameter constitutive models is useful for mathematical demonstration of cerebral vessel tissue behavior. In conclusion, good fitting of data illuminated that the use of multiple-parameter constitutive models is useful for mathematical demonstration of cerebral vessel tissue behavior.
Extensive brittle fracture curves are presented in the present paper for engineering components weakened by a U-shaped notch under different in-plane loading conditions from pure mode I to pure mode II. The curves were obtained in a computational manner on the basis of an appropriate brittle fracture model, namely the U-notched maximum tangential stress (UMTS) criterion, suggested and employed several times in the past by the author and his co-researchers to assess mixed mode fracture in numerous U-notched samples. Eight different notch tip radii were considered in the computations. Extensive brittle materials were also taken into consideration by using different values of the material critical distance in the calculations. By estimating theoretically the load-carrying capacity and the fracture initiation angle using solely the two basic material properties, namely the ultimate tensile strength and the plane-strain fracture toughness, engineers can design conveniently the U-notched brittle components and structures aiming to avoid abrupt fracture.
A state of the art instrumented Drop Weight Impact Tester Machine was developed in Iran University of Science and Technology which measures the energy absorption of composite materials under impact load. The output of the machine is used to draw load- time graph and calculate the amount of energy absorbed by the specimens. The machine was equipped with various sensor systems to measure the velocity of the impactor just before it contacts the specimen and the amount of contact force, and with a data acquisition system to record the force and time history. Capability of testing according to many different types of standards and capability of studying behaviour of the specimen after impact are two important characteristics of this machine. This designed system, after manufacturing and calibration, was installed and successfully utilized.