International Journal of Fracture Mechanics

An expression for the T-stress in a bi-material strip with a semi-finite interfacial crack is derived for general edge loads using a conservation integral method. The expression is explicit except for two non-dimensional constants, which are determined from a finite element analysis and which are tabulated as a function of the Dundurs’ parameters and the thickness ratio of the strip.

We describe an approach to predict failure in a complex, additively-manufactured stainless steel part as defined by the third Sandia Fracture Challenge. A viscoplastic internal state variable constitutive model was calibrated to fit experimental tension curves in order to capture plasticity, necking, and damage evolution leading to failure. Defects such as gas porosity and lack of fusion voids were represented by overlaying a synthetic porosity distribution onto the finite element mesh and computing the elementwise ratio between pore volume and element volume to initialize the damage internal state variables. These void volume fraction values were then used in a damage formulation accounting for growth of these existing voids, while new voids were allowed to nucleate based on a nucleation rule. Blind predictions of failure are compared to experimental results. The comparisons indicate that crack initiation and propagation were correctly predicted, and that an initial porosity field superimposed as higher initial damage may provide a path forward for capturing material strength uncertainty. The latter conclusion was supported by predicted crack face tortuosity beyond the usual mesh sensitivity and variability in predicted strain to failure; however, it bears further inquiry and a more conclusive result is pending compressive testing of challenge-built coupons to de-convolute materials behavior from the geometric influence of significant porosity.

The competition between fracture and plasticity in periodic hexagonal honeycomb structures subjected to (i) intercell cracking, (ii) intrawall cracking and (iii) transwall cracking is examined, and their effect upon the macroscopic collapse response is explored using dedicated FEM analyses of unit cell configurations. These three cracking mechanisms are regularly observed in wood microstructures, and insight into their influence on the macroscopic collapse behavior is necessary for adequately designing timber structures against failure. The numerical results are presented by means of collapse contours in the hydrostatic-deviatoric stress space, illustrating the effects of wall slenderness, relative fracture (versus yield) strength, and the relative size of the plastic zone at the crack tip. Both the hydrostatic and deviatoric collapse strengths of the honeycomb strongly increase in the transition from brittle cell walls with low relative fracture strength to ductile cell walls with high relative fracture strength. This strength increase typically changes the shape of the collapse contour, and is the largest for transwall cracking, followed by intercell cracking and finally intrawall cracking. The ultimate collapse strength of the honeycomb is significantly more sensitive to the fracture strength than to the fracture toughness of the cell walls, and correctly approaches the plastic yield surface under increasing relative fracture strength. The numerical results may serve as a useful guideline in the experimental calibration of the local fracture and yield strengths of cell walls in wood.

Fragmentation of brittle materials under high rates of loading is a commonly occurring phenomenon, but quantitative descriptions of the process have been elusive. Several models for dynamic fragmentation have been suggested in the past. In the present paper we consider two such models based on energy balance and compare their predictions of fragment size to the results of numerical simulations. This comparison shows that the energy-balance models lead to estimates of fragment size which are an order of magnitude larger than the calculated ones. These differences seem to be due to the fact that these energy-balance models deal with the onset of the fragmentation event; they do not include the time dependence of the process. In reality, fragmentation occurs over finite time during which energy continues to be supplied to the system, and cracks nucleate and propagate throughout the body. Therefore, we propose a model that includes the time history of the process and the number, distribution, and strength of flaws in the material. This model is studied by means of both simple analytical methods and computations. The results provide a consistent picture of fragmentation as a transient event.

This paper shows how the double-K fracture parameters K Ic ini and K Ic un can be determined for concrete using CT-specimens and wedge splitting specimens. The experimental results collected from the fracture tests the very large size CT-specimens and small size wedge splitting specimens carried out by many researchers are utilized to investigate the characters of the obtained double-K fracture parameters K Ic ini and K Ic un . It was found that the double-K fracture parameters K Ic ini and K Ic un determined from fracture tests on the large size CT-specimens are size-independent. And the values of K Ic ini and K Ic un determined from small size wedge splitting specimens with same dimensions are independent of the relative preformed notch length a0/D. However, when the dimensions of small size wedge splitting specimens change from 150×150×150 mm3 to 450×450×450 mm3, the values of K Ic ini and K Ic un slightly depend on the heights of the specimens and do not depend on the thickness of the specimens.

Remaining life estimation of components which experience elevated-temperature service requires knowledge of creep-crack-growth characteristics of the service-exposed material. In most cases only a small amount of material from in-service components is available for testing; thus, there is a need to design and benchmark test methods that use miniature creep-crack-growth specimens. In order to address this problem, a creep-crack-growth test methodology was developed using miniature single edge-notched tension specimens. The material used in this work was from a well characterized heat of Type 316 stainless steel, for which creep-crack growth data were previously obtained using conventional compact-tension type and center-cracked-tension type specimens. Good correlation was obtained between the crack growth rate and Cj, where Cj is the experimental counterpart of C*. The details of the analytic procedure for miniature specimens, particularly for small crack lengths, are presented. The current results agreed very well with those for large specimens as well as with creep-crack growth data obtained by other investigators.