Plain and nanofiber-interleaved glass/epoxy laminates clamped according to ASTM D7136 tested under impact loading to assess the improvement in impact resistance of composite laminates that have been interleaved by electrospun polyvinylidene ?uoride (PVDF) nanofibers with two different thicknesses. Composite specimens with stacking sequence [0/90/0/90]S were impacted at impact energy of 5J. Variation of the impact characteristics such as maximum contact load, maximum de?ection, maximum contact time, absorbed energy are depicted in the ?gures. The results showed that PVDF nanofibers are not a good choice for toughening epoxy and improving impact damage resistance of GFRP.

Generation of residual stress and structure deformation are the most important problems in the process of structure welding. Residual stresses inside and around the welded joints are harmful for integrity and proper functioning of the welded part. Tensile residual stresses near the weld zone may cause in developing brittle fracture, reduction of fatigue life or crack propagation caused by corrosion stresses. Welding residual stresses may even reach the yield stress of the part and can affect the thermal or mechanical working properties of it. Different thermal and mechanical approaches have been developed in the past in order to reduce these residual effects. Thus, both radiative and convective heat transfer methods have important roles in distribution of residual stresses during the welding process. In this study, convection and radiation effects on distribution of residual stress inside a welded part have been investigated for three different cases. In the first case, convection heat transfer was ignored and only effect of radiation on residual stress distribution was considered. In the second case, just the convection heat transfer applied on the model during the welding process. In another case, effects of radiation and convection heat transfer methods were investigated, simultaneously. Results of the current study showed that both radiative and convective heat transfer mechanisms have a significant share on distribution of residual stresses inside the welded part. It was also shown that the share of convection is greater than that of radiation heat transfer method.

Numerous failure curves are presented in this manuscript to predict the onset of sudden fracture in V-notched brittle materials under combined tension-shear loading conditions. The curves were developed in a computational manner in terms of the notch stress intensity factors and based on the suitable failure concept of the maximum tangential stress (MTS) utilized frequently in the past by the author and his co-researchers for predicting mixed mode brittle fracture in extensive notched specimens. Three extensively used notch angles and various notch tip radii were considered in the computations. A wide range of brittle materials were also taken into account by defining and using the material critical distance. Through predicting load-bearing capacity and notch bifurcation angle utilizing only the two basic material properties namely the ultimate tensile strength and the plane-strain fracture toughness, engineers can design more rapidly and conveniently the V-notched brittle components with the aim to withstand reliably against sudden fracture.

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.

Collide of two objects or impact, is one of the main damage initiation reasons. In this paper, impact and damage behavior of elastic and visco-elastic bodies are investigated numerically using the finite element analyses. The results showed that visco-elastic materials, distribute stresses to the edge of model after the impact with a solid body. Furthermore, the impact of elastic and visco-elastic composite materials are analyzed and the variations of stress, displacement, damage energy and the damage patterns during a time period are compared for the two material models. The reduction in the values of stress, displacement and damage energy of visco-elastic material is also determined relative to the elastic composite material.

In this paper, a differential quadrature element method (DQEM) is developed for free transverse vibration analysis of a non-uniform cantilever Timoshenko beam with multiple concentrated masses. Governing equations, compatibility and boundary conditions are formulated according to the differential quadrature rules. The compatibility conditions at the position of each concentrated mass are assumed as the continuity in the vertical displacement, rotation and bending moment and discontinuity in the transverse force due to acceleration of the concentrated mass. The effects of number, magnitude and position of the masses on the value of the natural frequencies are investigated. The accuracy, convergence and efficiency of the proposed method are confirmed by comparing the obtained numerical results with the analytical solutions of other researchers. The two main advantages of the proposed method in comparison with the exact solutions available in the literature are: 1) it is less time-consuming and subsequently moreefficient; 2) it is able to analyze the free vibration of the beams whose section varies as an arbitrary function which is difficult or sometimes impossible to solve with analytical methods.

The effects of mismatch parameters on isochromatic fringe patterns were studied using the technique of photoelasticity. First, the mathematical equations of isochromatic fringes were derived for singular stress field near a bi-material notch. These equations were used to study the effects of mismatch parameters on the shape of isochromatic fringes theoretically. Analytical results indicated that the mismatch parameters have a significant effect on the shape of the isochromatic fringe patterns around the bi-material notch tip. In order to assess the accuracy of the analytical results, a photoelastic test program was conducted on the V-notched bi-material Brazilian disc specimens. A very good agreement was shown to exist between the experimental results and the analytical reconstructions.