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Abstract: In this work fractography has been used to characterize the fracture surfaces of superelastic, notched round-bar NiTi-specimens. Several fractography studies have been performed for conventional materials, but only few studies have been conducted on NiTi-alloys. The aim of this work is to investigate the effect of semi-circular notches on the fracture behavior of NiTi. The main results indicate that the fracture process is a mixture of cleavage and micro-void coalescence, and that decreasing the notch-radius leads to a loss of ductility which manifests in a reduced fracture strain. Within the range of notches studied in this work, we can observe a transition from high scatter to low scatter in the fracture strain when reducing the notch-radius. By combining fractography studies, finite element analyses and the Rice–Tracey void-growth model, it is argued that fracture is most likely initiated close to the notch for all notch-radii studied herein, and that cleavage or quasi cleavage is the dominating fracture mechanism. [Copyright &y& Elsevier]

Abstract: An experimental study with total 504 specimens has been carried out to investigate the fracture and physical properties of the carbon anode materials. The specimens were sampled from anodes produced with machined stub holes. From normal-and Weibull analysis the fracture toughness and the tensile strength showed a clear temperature dependency and orthotropic behavior. It has been found that both the fracture toughness and tensile strength increases with the temperature and are larger for the specimens directed in the horizontal direction than in the vertical direction. The variation in the tensile strength within an anode decreased with the temperature but the variation in the fracture strain increased. The tensile strain appears to be only dependent on the temperature and insensitive to the routine anode properties of the anode material. A multivariate linear regression analyses of the fracture toughness and tensile strength has been conducted and a typical correlation of R 2 =0.5 (R is the Coefficient of Determination) to the measured routine anode properties was found. The thermal expansion coefficient is also larger in the vertical anode direction which makes the crack initiation more sensitive to temperatures. The orthotropic studies also showed that the air permeability has a tendency to be larger in the horizontal direction in the upper part of the anode which can induce unnecessary burning from the anode sides. The influence of the processing parameters in the paste plant and baking furnace has not been presented in this paper. [Copyright &y& Elsevier]

Abstract: It is well known that residual stresses influence the ductile fracture behaviour. In this paper, a numerical study was performed to assess the effect of residual stresses on ductile crack growth resistance of a typical pipeline steel. A modified boundary layer model was employed for the analysis under plane strain, Mode I loading condition. The residual stress fields were introduced into the finite element model by the eigenstrain method. A sharp crack was embedded in the center of the weld region. The complete Gurson model has been applied to simulate the ductile fracture by microvoid nucleation, growth and coalescence. Results show that tensile residual stresses can significantly reduce the crack growth resistance when the crack growth is small compared with the length scale of the tensile residual stress field. With the crack growth, the effect of residual stresses on the crack growth resistance tends to diminish. The effect of residual stress on ductile crack growth resistance seems independent of the size of geometrically similar welds. When normalized by the weld zone size, the ductile crack growth resistance collapses into one curve, which can be used to assess the structural integrity and evaluate the effect of residual stresses. It has also been found that the effect of residual stresses on crack growth resistance depends on the initial void volume fraction f 0, hardening exponent n and T-stress. [Copyright &y& Elsevier]

Abstract: A systematic study has been carried out by using 2D axisymmetric models to understand the ductile fracture behavior of pipes with internal and external circumferential cracks. Crack growth resistance curves have been computed using the complete Gurson model. Pipes with various diameter-to-thickness ratios, internal pressure, crack depths and material properties are analyzed. The results have been compared with those of corresponding SENT and standard SENB specimens. It clearly indicates that the SENT specimen is a good representation of circumferentially flawed pipes and an alternative to the conventional standard SENB specimen for the fracture mechanics testing in engineering critical assessment of pipes. [Copyright &y& Elsevier]

Abstract: A strong geometry dependence of ductile crack growth resistance emerges under large scale yielding. The geometry dependence is associated with different levels of crack tip constraint conditions. However, in a recent attempt to identify appropriate fracture mechanics specimens for pipeline steels, an “independent” relationship between the crack growth resistance curves and crack depths for SENT specimens has been observed experimentally. In this paper, we use the complete Gurson model to study the effects of crack depth and specimen size on ductile crack growth behavior. Crack growth resistance curves for plane strain, mode I crack growth under large scale yielding conditions have been computed. SENB and SENT specimens with three different specimen sizes, each specimen size with three different crack depths, have been selected. It has been found that crack tip constraint (Q-parameter) has a weak dependence on the crack depth for specimens in the low constraint regime. [Copyright &y& Elsevier]

Abstract: Residual stresses play a crucial role in structural integrity assessment. In this study, a large cracked cylinder with a weld in the center is applied to investigate the effect of residual stresses on the crack-tip constraint. A modified boundary layer model with a remote displacement-controlled elastic K-field and T-stress under small scale yielding has been used to simulate the problem. A two-dimensional tensile residual stress field due to the weld is introduced into the model by the so-called eigenstrain method. It has been shown that the residual stresses can significantly elevate the crack-tip constraint and thus increase the probability for cleavage fracture. The constraint parameter R introduced by the authors can be used to rank the crack-tip constraint induced by the bi-axial residual stresses. The R value decreases with the increase in the applied J-integral. The residual stress-induced constraint is also coupled with the T-stress. The R value becomes smaller with larger T-stress. [Copyright &y& Elsevier]

Abstract: This study focuses on the stress intensity factors for free edges in multi-layered structural components. The effects of elastic constants of various material combinations on the weak singularity at free edges are analyzed. Using the H-integral approach, the effects of elastic mismatch parameters, the bond area and the thickness of the thin metal layer on the stress intensity factor are quantified and the results are compared with detailed finite element solutions. A good agreement between numerical predictions obtained from the H-integral and the detailed FE results is achieved, showing the applicability of this approach. Similar to a crack problem, the singular elastic field dominates in an annular region adjacent to the notch tip. The relationship between the valid range of the K-dominated field and the thin-film thickness is then demonstrated. Furthermore, the competition of crack initiation between the free edge interface (180° opening angle) and a 90° notch interface in a generic specimen is investigated, in order to find out which is the prevailing failure mode. Comparison between isotropic Si and anisotropic Si substrate is also illustrated. Anisotropy of the Si substrate has a significant influence on the stress intensity factor when combined with an Au or Al metal layer but not with a Cu layer. Additionally, standardized numerical formulae of the dimensionless stress intensity factor have been derived to guide the engineering application. [Copyright &y& Elsevier]

Cross weld tensile testing is widely used in the industry to qualify welds. In these conventional testing fracture load is measured and the location of fracture (weld metal, base metal or heat affected zone) is evaluated. Because the load-elongation curve depends on the location of fracture and the initial gauge length, it cannot be utilized in the failure assessment of weldments. Failure assessment of weldments requires input of true stress–strain behaviour for each material zone. In this paper, a notched cross weld tensile testing method is proposed for determining the true stress–strain curve for each material zone of a weldment. In the proposed method, cylindrical cross weld tensile specimens, with a notch located either in the weld metal, base metal or possibly heat affected zone are applied. Due to the notch, plastic deformation is forced to develop in the notched region. A load versus diameter reduction curve is recorded. It has been shown that the true strain at maximum load is independent of the notch geometry. Furthermore, the materials true stress–strain curve can be determined from the recorded load versus diameter reduction curve of a notched cross weld tensile specimen by dividing a geometry-factor G, which is approximated by a quadratic function of the specimen diameter to notch radius ratio and a linear function of the true strain at the maximum load. It is found that G is independent of the material zone length when the homogenous material length is larger or equal to the minimum diameter. [Copyright &y& Elsevier]

Abstract: Compression behaviours of individual micron-sized acrylic particles have been studied by using a nanoindentation-based method with a flat-end tip, instead of a commonly used sharp tip. The effect of loading rate on the mechanical properties of the high monodisperse acrylic particles, such as K-value, breaking force and breaking displacement, has been investigated. A wide range of loading rate conditions has been applied to examine the sensitivity of selected mechanical properties. It has been observed that the loading rate has a significant effect on K-value and breaking force whereas breaking displacement is independent of loading rate. These results facilitate the industrial applications of acrylic particles. [Copyright &y& Elsevier]

Highlights: [•] It is shown that the geometrical nonlinearity of silicon wafers affects the SIFs significantly. [•] The FE analysis illustrated some limitations with the Newman–Raju approach in calculating SIFs for thin wafers. [•] The results showed that the Newman–Raju solution predicts vanishing SIFs of the surface point (ϕ =0) for long surface cracks . [•] The results show that for long surface cracks, finite element modeling is necessary for calculating the SIFs. [Copyright &y& Elsevier]

Highlights: [•] Multi-dimensional graphitic nanostructures are constructed by spanning fullerenes with CNTs. [•] Mechanical characteristics are governed by the inter-fullerene distance. [•] Both 2D nano-mesh and 3D nano-truss exhibit a negative Poisson’s ratio. [•] Tunable Poisson’s ratio ranges from negative to positive to negative when stretched along 〈110〉 direction. [Copyright &y& Elsevier]