Crack growth pattern analysis of monolithic glass ceramic on a titanium abutment for single crown implant restorations using smooth particle hydrodynamics algorithm

Background. Glass ceramic materials have multiple applications in various prosthetic fields. Despite the many advantages of these materials, they still have limitations such as fragility and surface machining and ease of repairing. Crack propagation has been a typical concern in fullceramic crowns, for which many successful numerical simulations have been carried out using the extended finite element method (XFEM). However, XFEM cannot correctly predict a primary crack growth direction under dynamic loading on the implant crown. Methods. In this work, the dental implant crown and abutment were modeled in CATIA V5R19 software using a CT-scan technique based on the human first molar. The crown was approximated with 39514 spherical particles to reach a reasonable convergence in the results. In the present work, glass ceramic was considered the crown material on a titanium abutment. The simulation was performed for an impactor with an initial velocity of 25 m/s in the implant-abutment axis direction. We took advantage of smooth particle hydrodynamics (SPH) such that the burden of defining a primary crack growth direction was suppressed. Results. The simulation results demonstrated that the micro-crack onset due to the impact wave in the ceramic crown first began from the crown incisal edge and then extended to the margin due to increased stress concentration near the contact region. At 23.36 µs, the crack growth was observed in two different directions based on the crown geometry, and at the end of the simulation, some micro-cracks were also initiated from the crown margin. Moreover, the results showed that the SPH algorithm could be considered an alternative robust tool to predict crack propagation in brittle materials, particularly for the implant crown under dynamic loading. Conclusion. The main achievement of the present study was that the SPH algorithm is a helpful tool to predict the crack growth pattern in brittle materials, especially for ceramic crowns under dynamic loading. The predicted crack direction showed that the initial crack was divided into two branches after its impact, leading to the crown fracture. The micro-crack initiated from the crown incisal edge and then extended to the crown margin due to the stress concentration near the contact area.

3D Textural Analysis of Fatigue Fracture Surfaces

Three CT specimens from stainless steel AISI 304L were subjected to constant amplitude cyclic loadings with various asymmetries. Crack growth was recorded in detail. Fracture surfaces were documented by 3D maps in about 110 locations in the crack growth direction. 3D maps and their local gradients were represented by 2D wavelet decompositions in 10 levels resulting in 60 textural features. Statistical models expressing crack growth rate as a function of textural features were optimized. Training and testing approach, a high ratio of overfitting, and testing of significance of components ensured model's robustness. Quality of results is documented by graphs confronting model outputs with real data known from experiment. Results are acceptable in all cases.

A roll-bending approach to suppress the edge cracking of silicon steel in the cold rolling process

The range of roll-bending that inhibits the edge cracking of high-silicon (3.0 wt%) steel strip during cold rolling was investigated by performing a pilot cold rolling test. In the rolling test, roll-bending was emulated by lathe-machining the work roll surface to be concave (corresponding to negative roll-bending) or convex (corresponding to positive roll-bending). Crack growth length that propagated during rolling and crack growth direction were measured. Three-dimensional finite element analysis coupled with ductile fracture criterion was conducted to predict the crack growth length and crack growth direction. The reliability of the finite element analysis was verified by comparing the predictions with measurements. A series of finite element simulations were then conducted with different levels of roll-bending, expressed as the ratio of the radius of curvature of work roll surface ( R) to its barrel length ( L).The difference between the measurements and the predictions of the crack growth length and crack growth direction was 6.5% and 8.3%, respectively, when the initial notch length was 6 mm. Even if a high reduction ratio for a given pass was applied to the silicon steel strip, edge cracking did not occur if the L/ R ratio was less than −0.15, with a negative value corresponding to a concave surface profile, representing negative bending.