International Journal of Damage Mechanics

In this study, a failure analysis of glass-epoxy laminated composite bolted-joints with bolt/hole clearance under various torques was carried out. To estimate the effects of joint geometry and fiber orientation on the failure strength and failure mode, parametric studies were conducted experimentally. The two different geometrical parameters were the edge distance-to-hole diameter ratio (E/D) and plate width-to-hole diameter ratio (W/D), E/D ratio was selected from 1 to 5, and W/D ratio was chosen from 2 to 5. The bolt preload torque was also carried out as 0, 3, and 6 Nm. To investigate the material parameters effect, laminated plates were oriented as three different stacking sequences [90^o]₈, [45^o]₈, and [0^o] ₈. The experiments were carried out with a clearance between the diameters of the bolt and the circular hole of 5 and 6 mm, respectively. According to experimental results, failure mode and bearing strength are strongly influenced by both material parameters and geometrical parameters. Additionally, when a torque is applied to the bolted-joints, the failure mechanism is affected by its increasing values.

The article deals with the relations between microstructural parameters, microscopic fracture mechanisms, and resultant plane-strain fracture toughness, K_IC, of hot-forged 7000 alloy plates in overaged condition. Three industrially produced alloys with the (Zn + Mg + Cu) content of ∼11.5 mass% and different contents of (Fe + Si) impurities (from 0.23 to 0.37 mass%) were used. The variation in alloy purity generated differences in the geometric characteristics of coarse intermetallic phase particles, exerting significant effect on fracture behavior of these alloys. To evaluate the fracture mechanism, characterization of the broken K_IC test specimen surfaces was performed using scanning electron microscopy. Three micromechanisms governing fracture process were identified. The extent of primary voiding at coarse intermetallic phase particles increases systematically with the increase of (Fe + Si) level, whereas the extent of intergranular/transgranular fracture decreases. This observation was confirmed by a quantitative description of fractures by means of a profilometric method. It was found that morphological parameters of the fracture profiles clearly differentiate between different fracture modes and offer conclusive proof that coarse voiding at fractured intermetallic phase particles dominates fracture at low alloy purity. A higher fraction of coarse voiding is shown to result in an overall reduction of fracture toughness.

An image-processing method for damage assessment of ceramics after an impact is presented in this article. The method is based on the analysis of digital gray-scale images of the damaged surfaces and consists of successive steps of image enhancement, including normalization of light intensity, rotation of the light intensity space, histogram equalization, thresholding, and determination of the parameter characterizing the density of image distortions. The method allows the use of digital images taken under imperfect lighting conditions. The method was applied for damage assessment of AD995 ceramic specimens. The specimens were subjected to a double pulse loading generated with the help of the split Hopkinson pressure bar. As evident from the analysis of experiments, the parameter density of surface image distortions correlates strongly with the amplitude of the incident strain pulse as well as with the descriptive characteristics of the deformed shape of the specimen.

Improvement in the short-term behavior of deficient reinforced concrete beams is very well known through extensive testing of reinforced concrete beams strengthened by externally bonded carbon fiber reinforced polymer strips. However, long-term performance of such beams needs to be assessed before the method can gain full acceptance. Prominent modes of failure in strengthened reinforced concrete beams reported in literature are concrete crushing in compression, carbon fiber reinforced polymer plate rupturing in tension and peeling of the carbon fiber reinforced polymer plate due to high interfacial shear and peeling stresses at the plate cut-off point. Modeling of the overall system of strengthened reinforced concrete beams requires modeling of the individual components that ultimately leads to failure i.e., concrete, carbon fiber reinforced polymer and concrete - carbon fiber reinforced polymer. Component elasto-damage constitutive models are developed for concrete crushing, carbon fiber reinforced polymer rupture and concrete-carbon fiber reinforced polymer interface failure, calibrated by data from both suitably designed experiments and from experiments reported in literature, and are utilized to investigate the low cycle fatigue behavior of reinforced concrete beams strengthened by carbon fiber reinforced polymer strips. The predictive ability of the model is tested by comparison to data from two different beam strengthening schemes i.e., with end anchorage and without end anchorage.

A model for simulating fatigue damage accumulation and the fatigue failure process in metals is presented. The simulation is achieved by modeling material behavior with a series of nonlinear mechanical springs with randomized behavior. With each applied stress, a certain number of springs rupture. The damage accumulation process is modeled by the number of springs that have ruptured during the entire stress application cycle. When a sufficiently large number of springs rupture, the entire system is considered to have failed. This constitutes fatigue failure. This article follows two previous publications by the first two authors and extends the model further by incorporating additional random variables, investigating the significance of uncertainty in the spring behavior and simulation of the hysteresis behavior of metals during the fatigue damage accumulation process. Results similar to (1) the Wöhler S—N curve and (2) the hysteresis loss versus the number of stress cycle relationship, observed in laboratory testing of metal specimens, are presented.

It had been long recognized that the tensile strength of brittle materials increases with increase of the loading rate. In the present article, a statistical approach to rupture of a disordered 2D triangular truss lattice consisting of fragile nonlinear springs is attempted in hope to elucidate some generic effects of structural and geometrical disorder on the tensile strength and the (stress-peak and post-peak) damage energy rates. The simulation results reveal increase of the mean and decrease of the standard deviation of the macroscopic tensile strength with increase of the structural and geometrical order till the ‘theoretical strength’ saturation. At the same time, the increase in lattice disorder results in increase of the mean and standard deviation of the stress-peak damage energy rate, followed by the decrease of the same in the softening regime.

The previously developed closed form expressions for thermo-elastic properties of laminates with intralaminar cracks (Lundmark and Varna, 2005) contain crack surface opening and sliding as main local parameters. The dependence of these parameters on various material and geometrical characteristics was in (Lundmark and Varna, 2005) described by power functions valid only for noninteractive cracks in a given layer (low crack density). In this article the 90-layer crack interaction in terms of its effect on the crack opening displacement (COD) is discussed. The effect on COD is described by the introduced ‘interaction function’ which is determined fitting results of finite element (FE) analysis for cross-ply laminates. To simplify the application in stiffness predictions, the numerically found weak dependence of the interaction on geometrical and material parameters is neglected and the interaction function is presented as a function of crack density only. Using the interaction function to determine the COD, the previously developed calculation scheme (Lundmark and Varna, 2005) has been used to predict stiffness reduction in the entire crack density region. The results are validated comparing with tests and FE simulations.

The article deals with the effect of stress triaxiality on the inelastic deformation behavior of aluminum alloys. The proposed continuum model takes into account a stress-triaxiality-dependent yield condition as well as a damage criterion with different branches corresponding to various damage modes depending on the stress triaxiality and the Lode parameter. Numerical simulations of experiments with smooth and pre-notched tension and shear specimens are presented covering a wide range of stress triaxialities. Numerical results show good agreement with available experimental data. The analyses allow verification of the macroscopic model and identification of material parameters.