Assay of Secondary Anisotropy in Additively Manufactured Alloys for Dental Applications

Even though additive manufacturing (AM) techniques have been available since the late 1980s, their application in medicine is still striving to gain full acceptance. For the production of dental implants, the use of AM allows to save time and costs, but also to ensure closer dimensional tolerances and higher repeatability, as compared to traditional manual processes. Among the several AM solutions, Laser Powder Bed Fusion (L-PBF) is the most appropriate for the production of metal prostheses. The target of this paper was to investigate the mechanical and microstructural characteristics of Co–Cr–Mo and Ti–6Al–4V alloys processed by L-PBF, with a specific focus on secondary anisotropy that is usually disregarded in the literature. Tensile specimens were built in the EOSINT-M270 machine, along different orientations perpendicular to the growth direction. Density, hardness, and tensile properties were measured and the results combined with microstructural and fractographic examination. For both alloys, the results provided evidence of high strength and hardness, combined with outstanding elongation and full densification. Extremely fine microstructures were observed, sufficient to account for the good mechanical response. Statistical analysis of the mechanical properties allowed to attest the substantial absence of secondary anisotropy. The result was corroborated by the observations of the microstructures and of the failure modes. Overall, the two alloys proved to be high-performing, in very close agreement with the values reported in the datasheets, independently of the build orientation.

Investigation of Fracture Process of S355JR Steel in Transition Region Using Metallographic and Fractographic Tests and Numerical Analysis

In the paper are presented test results of fracture process in brittle-to-ductile transition range for two microstructural types of S355JR steel – ferrite-pearlite and ferrite-carbides. For both kinds of S355JR steel obtained in temperature range of transition region the strength and plastic properties are similar, but the fracture toughness characteristics showed significantly are various. To clarify the differences in the course of trends in the mechanical characteristics performed metallographic and fractographic observations using the scanning electronic microscope. The fractographic examination showed that changes in the fracture surface morphology were dependent on the test temperature. It was also found that during the subcritical crack growth the region of ductile fracture extension reduced with decreasing temperature. The results of finite element method (FEM) calculation the stress fields in front of the crack of single edge notch in bending (SENB) specimens in the range of brittle-to-ductile transition are presented also. The FEM calculations were performed on the numerical model of SENB specimen using the ABAQUS program.

Fractographic Evaluation of the Metallic Materials for Medical Applications

The manner of studying of the fracture modes could be done through fractography. Fractography is the study of fracture surface morphologies and it gives an insight into damage and failure mechanisms, underpinning the development of physically-based failure criteria. In composites research it provides a crucial link between predictive models and experimental observations. Fractographic methods are routinely used to determine the cause of failure in all engineering structures, especially in product failure and the practice of forensic engineering or failure analysis. In material science research, fractography is used to develop and evaluate theoretical models of crack growth behavior. One of the aims of fractographic examination is to determine the cause of failure by studying the characteristics of a fracture surface. Different types of crack growth produce characteristic features on the surface, which can be used to help identify the failure mode. The overall pattern of cracking can be more important than a single crack, however, especially in the case of brittle behavior materials. Initial fractographic examination is commonly carried out on a macro scale utilizing low power optical microscopy and oblique lighting techniques to identify the extent of cracking, possible modes and likely origins. When it is needed to identify the nature of failure, an analysis at high magnification is required and scanning electron microscopy (SEM) seems to be the best choice. The problem of fracture behavior of biometallic materials is a real one, being well and repeatedly presented in literature. Variations in alloy compositions can lead to subtle differences in mechanical, physical, or electrochemical properties. However, these differences are minor compared with the potential variability caused by differences in fabrication methodology, heat treatment, cold working, and surface finishing, where surface treatments are particularly important for corrosion and wear properties. The aim of this paper, therefore, is to summarize the different types of metals and alloys used as biomaterials, the corrosion of metals in the human body, and different failure damages of metallic implants.

Corrosion Fatigue Behavior of Mooring Chain Steel in Seawater

With a majority of the reported chain failures related to fatigue, this phenomenon is one of the main topics to be studied as part of Mooring Integrity Management. Present fatigue design is mainly based on fatigue curves for chains under tension-tension loads in seawater. However, the applicability of these curves for different loading modes and specific environments remains unclear. This paper studies the fatigue behavior of the material used on chains as it builds the baseline for the performance of these mooring components. It includes uniaxial fatigue tests that were undertaken on R4 and R5 steel grades obtained from actual chains after all their manufacturing steps. Samples were not only tested in air and in synthetic seawater but different corrosion related parameters were also studied: frequency, temperature and cathodic protection. From the results of these tests, separated SN curves were obtained. Subsequently, these curves were analyzed and compared against present recommended design curves for material. Fractographic examination was undertaken to assess the effect of corrosion and cathodic protection and comparison between material and component response was also addressed. Results showed the strong synergy between corrosion and fatigue. Also, the improvement from fatigue design curves to actual response of the materials was quantified.

Mechanical and Shielding Properties of an As-Cast New Pb-B Shielding Composite Materials

The new type of Pb-B shielding alloys with high tensile strength and hardness were prepared by casting. The microstructure and morphology of the Pb-B alloys were investigated by scanning electron microscope (SEM) analysis. Mechanical properties and radiation shielding effect of the alloys were compared with other Pb-based shielding alloys. The results indicate that the tensile strength and hardness increased up to 116 MPa and 160 HB with the 1.0 wt.% content of B. The fractographic examination conducted by SEM indicate that the Pb-B alloys are in form of plastic fracture, and the fracture model changes from the dimple to the intergranular quasi-cleavage with the increasing of B content. Furthermore, the composites are of the excellent shielding properties. Especially at the thickness of 20 mm, the shielding ratios for γ-ray and neutron reach 49.7% and 92.7%, respectively.

Study of Aggregate Size Effect on Fracture Toughness of Petreous Macrocomposites (Concrete)

The present study investigates the effect of rock aggregate size on the fracture toughness of a petreous macrocomposite material (concrete). The effect of aggregate size on the fracture properties of concrete was studied by analysing the fracture toughness KIC results obtained using single edge notched beam (SENB) specimens submitted to 4-point bending test. The results were obtained according to the methodology proposed by Srawley and Gross for monolithic ceramic materials. Additionally, the effect of aggregate size has been analysed by performing fractographic examination of unnotched beam specimens also submitted to 4-point bending test. KIc values obtained via linear elastic fracture mechanics (LEFM) theory applied to the fractographic data were comparable to those obtained by SENB method. The obtained results show that the fracture toughness of concrete depends on the aggregate particle size, although KIC is not linearly related with the particle size. Fracture behaviour depends on the interaction between the used mortar (a mixture of portland cement with sand and water) and the different rock (aggregate) particle sizes. This kind of studies allows further extending the knowledge on the failure mechanisms of concrete, which permits to improve the characteristics of these macrocomposite materials by understanding the effects related to the modification of their structure.

Residual Strength and Fracture Path for Drilled Epoxy-Glass Composites

Aircraft composite structures are mostly joined by mechanical fasteners like bolts, pins or screws. However, the effect of the presence of holes in the remaining strength of the composite structures is still being studied extensively. In this work, epoxy/glass laminates with drilled holes of different sizes were tensile tested and from these results, the residual strength was plotted. Strength vs. hole’s diameter at different fiber orientation was obtained. The fracture path and failure mechanism were identified by fractographic examination. The Point Stress Criterion (PSC) was used, in order to establish the stress intensification due to the presence of a drilled hole. A numerical model by Finite Element Method was carried out to verify the experimental results and the analytic failure predictions. A reduction of 50% in laminate strength was observed when diameter-width ratio was 0.12. The principal fracture mechanism observed in composite laminates was interface breakup. FEM results and analytic results by PSC show accuracy of 90% for predicting the damage in drilled composites.