Fatigue damage and life evaluation of thick bi-material double strap joints for use in marine applications

The present-day interest in the use of composite-steel joints in primary marine applications requires an in-depth knowledge of the fatigue performance of thick adhesive joints. This paper reports on experimental tests, quasi-static and fatigue, performed on unaged and aged bi-material double strap joints with thick adhesive bondlines. The specimens are monitored by Digital Image Correlation and Infrared Thermography techniques to evaluate the types and extent of damage that occur in the joint during fatigue loading. The S-N curve of the aged joint is evaluated along with it’s fatigue limit. It is found that the unaged specimens fail due to cohesive damage, hackles and disbond at the adhesive-adherend interface and the aged specimens failed due to delamination within the composite. The specimens that survived fatigue loading showed similar residual strength as specimens that were not fatigue loaded.

Evaluation of Water Flow on Interfacial Strength in PSA Film Delamination

To model the peeling phenomenon during cataract surgery and examine the effect of fluid flow during surgery, we constructed a simplified physical system and compared the case where only static pressure is applied to the adhesive thin film and the case where water flow is applied to the film by suction. From experiments with and without suctioning, the energy release rates of the adhesive thin film were calculated to be approximately 10 N/m, and no significant difference was confirmed with or without suction. We modeled the peeling phenomenon using the cohesive damage model and performed a finite element analysis considering the coupling of the fluid and membrane. The simulation results without suction were in good agreement with the theoretical values of the stress and deflection. When the water flow was applied to collide with the peeling part, the film deflection at the center became smaller, and the radial and circumferential stresses became smaller. From this result, it is shown that the stress acting on the membrane surrounding the crystalline lens can be reduced and peeling can be performed by successfully using the water flow for peeling.

Inter-Relationship between Coating Micro/Nanostructure and the Tribological Performance of Zr–C Gradient Coatings

The research presented in this article concerns Zr–C gradient coatings that were deposited on HS6-5-2 steel by reactive magnetron sputtering from the Zr target in appropriately programmed C2H2 mass flow rate, resulting in various profiles of atomic carbon concentrations in the coating and consequently in spatial change of the properties (H, E, …) and behavior (H/E, H3/E2, We). In particular, the characteristic changes in hardness and Young’s modulus in the Zr–C coatings represented approximately by the bell curve, which has a maximum at the content of about 50 at.% C, were an inspiration to study the behavior of gradient coatings with carbon content in the range of 0–50 and 50–85 at.% with the same hardness change profile. The obtained results indicate that, firstly, the gradient of spatial changes in the coating composition increases their resistance to cohesive damage in comparison to non-gradient coatings, and, secondly, the results show that high hardness is a desired property but not sufficient to ensure adequate coating performance. Independently, an appropriate nano/microstructural structure is necessary, which determines their tribological behavior. In particular, in the case of the tested Zr–C coatings, the obtained results indicate that gradient coatings with a carbon content in the range of 50–85 at.% have better properties, characterized by the critical force Lc2, wear, coefficient of friction, H/E and H3/E2 ratios.

Numerical Investigation to Quantify the Rate of Damage within Mortar Bituminous Materials: Modeling of Cracks Initiation and Propagation

Asphalt concrete is highly used to construct pavement layers in the civil engineering field. It is defined as a complex medium composed of aggregates (inclusions), mortar (matrix) and air void. The mortar itself is a mixture of fillers, sand and bitumen. Furthermore, mortar is the phase that links the coarse aggregates. In general, fracture of asphalt concrete occurs within mortar or among aggregate-mortar interface. Therefore, two types of fracture can be identified, i.e., adhesive and cohesive damages. The first type is occurred among the interface of aggregate-mortar. The second is taken place within the mortar. This paper presents numerical investigations of the damage initiation and stiffness degradation within the asphalt concrete matrix. Numerical simulations were carried out to investigate, firstly, how damage is initiated and developed, and then, to simulate how cracks can be initiated and propagated within this material. Cohesive finite elements method was adopted to simulate fracture. For adhesive damage, the model was represented by one rectangular aggregate that is linked to the asphalt concrete thanks to a thin layer of the mortar. For cohesive damage, the model was considered as a thick layer of the mortar in between two coarse aggregates. The applied loading was derived from the speed of traffic vehicle. A comparative analysis between four mortars was conducted. The effect of loading and the type of mortar on damage initiation and stiffness degradation will be shown. Moreover, the initiation and propagation of cracks as function of loading and stiffness modulus will be illustrated.