Degradation Behavior Of Materials Research Articles

Mechanical degradation of duplex SiC-fiber reinforced SiC matrix composite tubes under a controlled high-temperature steam environment

This paper describes results from the mechanical evaluation of unirradiated SiC fiber–reinforced SiC matrix composite tubes under a controlled high-temperature steam environment. The experiments were aimed at identifying key material degradation behavior under environments relevant to loss-of-coolant accidents of light water reactors. Mechanical tests of the SiC composite tubes at 1000 °C under steam and inert environments were conducted using a unique test capability. The material tested was a duplex tube with a thick monolithic SiC layer on the outer surface. The tubes were subjected to preloading at ∼100 MPa in tension before exposure to high-temperature steam with up to 75 % of the preload at a constant displacement. In the presence of matrix cracks, the steam exposure caused embrittlement of the SiC composite tubes and failure at a stress level below the pretest stress. The material degradation was explained by a fiber oxidation model, which can be applied to various SiC cladding concepts. The embrittlement could be a limiting factor for using SiC cladding subjected to loss-of-coolant accident conditions.

Fastening solutions on composite structures: Progressive damage analysis of a unique bolted joint design for single-lap CFRP laminate

This study tested a unique assembly method using single and multi-body sleeves with carbon fiber-reinforced plastic (CFRP) to improve load-carrying capacity in single-lap joints. Advanced techniques were implemented into FE code to simulate progressive material degradation behavior. Ti6-4 bolt, insert, and washers with AISI 304L sleeve joint were conceptually designed to keep bolt and nut together with less relative motion. Failure indices were reduced by 16–54%, damage initiation force was improved by 8–40%, and inter-plate clamp loss was reduced by 18% compared to the sleeveless design. Lateral load-carrying capability of joint and inter-plate clamp load significantly improved.

Biodegradable materials: Foundation of transient and sustainable electronics

Biodegradable materials are designed to degrade in a desired time either through the action of microorganisms or under certain physical conditions. The driving force behind the rise of biodegradable materials is the growing problem of electronic waste (e-waste), low recyclability, and toxicity of electronic materials. Transient response of biodegradable materials has found application in next-generation health-care and biomedical devices. Advances in material science and manufacturing technique have pushed the envelope of innovation further. This review discusses different biodegradable material classes that have emerged to replace the traditional non-biodegradable materials in electronics. Focus has been given to conversion of biodegradable materials to inks and pastes that find use in printed electronics to create flexible, bendable, soft, and degradable devices. Material degradation behavior and dissolution chemistries have been illustrated to understand their impact on electrical performance of devices. Finally, some short-term and long-term challenges are pointed out to overcome the commercialization barrier.

True stress-strain curve extraction from ion-irradiated materials via small tensile, small punch and nanoindentation tests: method development and accuracy/consistency verification

Ion irradiation has been widely used to emulate material degradation behavior in reactor environments. Due to the limited depth of ion-irradiated layers, post-irradiation mechanical properties are mostly characterized by miniature test techniques, such as small tensile, small punch and nanoindentation tests. Although limited, the penetration depth of high-energy ions is possible to be ‘large’ enough to cover many grains. In such cases, it is possible to extract ‘bulk’ stress-strain curves from the ion-irradiated volumes, since they are now capable of reflecting bulk material behavior. One of the widely used extraction approaches is inverse finite element method (iFEM). However, the extracted curves by iFEM may contain significant errors in such cases due to some adverse effects, e.g. large scatter in the tensile curves for small tensile test, and indentation size effect (ISE) and strain rate effect (SRE) for nanoindentation test. In order to overcome these negative influences, we proposed different solutions for each test technique. For small tensile test, digital image correlation (DIC) was used to improve the accuracy, by directly obtaining the local true strain in the weakest section, and thereby the local true stress. For nanoindentation test, a two-step correction-conversion method was proposed to refine the iFEM-extracted curves. The three sets of test and data-processing schemes were quantitatively evaluated to check their accuracy and consistency for both pristine and ion-irradiated materials. The extractions from the pristine material show that, all the schemes are capable of providing true stress-strain curves with good accuracy, as they exhibit little deviation from those by the standard specimen. After ion irradiation, although the mechanical behavior has changed drastically, these schemes still exhibit good consistency among the extracted curves. These findings verify the accuracy and consistency of the three approaches with the new developments to obtain ‘bulk’ true stress-strain curves from the ion-irradiated materials.

Electrochemical behavior and surface characterization of dental materials in artificial salivary

Research concerning the applications of ceramic biomaterials as dental restorative materials is of particular interest for the study of the physico-chemical, mechanical and microstructural behavior with a multitude of techniques. Nevertheless, the wealth of scientific articles in this field remains vast and poor in terms of all-ceramic restorative materials, their ageing and electrochemical degradation behavior utilizing the electrochemical impedance spectroscopy, in contact with an electrolytic solution which can cause and exhibit a very remarkable variation in the surface state and variation in the stability of the electrochemical behavior of these dental materials, which can be influenced by pH, temperature and the medium variations. Ringer's solution as artificial saliva has been used as a degradation medium to evaluate the effect of saliva on the microstructure, surface condition, chemical composition and degradation behavior of dental materials. This is done using X-ray diffraction, SEM-coupled energy dispersive spectrometry (EDX) and electrochemical impedance spectroscopy as a technique to assess the interface degradation behavior of these materials after 21 days of immersion in salivary medium. The aim of this study was to identify and evaluate the changes in the electrochemical behavior of these 2 ceramic materials, Feldspar and Alumina after immersion in Ringer solution for 7, 14, 21 days at 37 °C and pH = 7.3 by XRD, SEM / EDX and their electrochemical behavior by EIS. These results indicate that there is a significant effect of synthetic Ringer's salivary solution on the ceramics studied; this effect is manifested by degradation through the release and/or dissolution of certain ionic compounds. It is also important to note that this dissolution could result in the deposition of layers on the surface of dental materials; this is even more important depending on the immersion time.

Multiscale Damage Evolution Analysis of Aluminum Alloy Based on Defect Visualization

The evaluation of fatigue life through the mechanism of fatigue damage accumulation is still a challenging task in engineering structure failure analysis. A multiscale fatigue damage evolution model was proposed for describing both the mesoscopic voids propagation in the mesoscopic-scale and fatigue damage evolution process, reflecting the progressive degradation of metal components in the macro-scale. An effective method of defect classification was used to implement 3D reconstruction technology based on the MCT (micro-computed tomography) scanning damage data with ABAQUS subroutine. The effectiveness was validated through the comparison with the experimental data of fatigue damage accumulation. Our results indicated that the multiscale fatigue damage evolution model built a bridge between mesoscopic damage and macroscopic fracture, which not only used the damage variable in the macro-scale to characterize the mesoscopic damage evolution indirectly but also understood macroscopic material degradation behavior from mesoscale with sufficient precision. Furthermore, the multiscale fatigue damage evolution model could offer a new reasonable explanation of the effect of load sequence on fatigue life, and also could predict the fatigue life based on damage data by nondestructive testing techniques.

Study on the effect of modified and unmodified silica on the properties of natural rubber vulcanizates

AbstractIn the article, the effects of silica (silicon oxide) on some properties of natural rubber (NR) were studied. Silica used are unmodified (SiKBT) and modified with triethoxi silane propyl tetrasunfite (SiBT). It is shown SiBT increases vulcanization network density (VND), so it enhances strength and elastic properties of NR. In contrary, SiKBT decreases VND and reduces, but has almost no effect on strength of NR. Silica, both modified and unmodified, are assumed to improve network regularity of NR that change thermal degradation behavior of materials and keep the strength of NR‐SiKBT compound unchanged.

Thickness dependent structural ordering, degradation and metastability in polysilane thin films: A photoluminescence study on representative σ-conjugated polymers

We present a fundamental experimental study based on the fluorescence investigation of thin σ-conjugated polymer films, where the dependence of optoelectrical properties and UV degradation on film thickness ranging from nano- to microscale was studied. Such extensive and detailed study was performed for the first time and observed spectral shifts in emission and excitation spectra and UV degradation retardation point towards the conclusions that there exists a threshold thickness where the material degradation behavior, electron delocalization and structure suddenly change. The development of well aligned polymeric chain structure between the nano- and micrometer thickness (on the mesoscale) was shown responsible for the manifested phenomena. The material thicker than critical 500nm has extremely small Stokes' shift, maximum extended σ-delocalization along the silicon polymer backbone and exhibits remarkable UV degradation slowdown and self-recovery ability. On the contrary, the electronic properties of thin films below 80nm resemble those of random coils in solutions. The films of moderate thickness show relatively steep transition between these two modes of structural ordering and resulting properties. Altogether, we consider this complex phenomenon as a consequence of the mesoscale effect, which is an only recently introduced concept in polymer thin films.

Meso-scale image-based modeling of reinforced concrete and adaptive multi-scale analyses on damage evolution in concrete structures

This paper presents new image-based multi-grid and adaptive multi-scale modeling methods to simulate trans-scale process of reinforced concrete (RC) from evolving random meso-damage to macro-scopic cracks and eventually to catastrophic rupture. Adaptivity ensures continuous scale changes in the model due to evolving damage without user’s intervention in the computation. The methods provided an effective numerical tool to understand macroscopic material degradation behavior from meso-scale with sufficient precision. Through cases study, the results shows that the developed methods can be used to reveal well the failure mechanisms of RC by considering the real random heterogeneous meso-structures within material as well as better computational efficiency.

Synthesis, Characterization, and Hydrolytic Degradation of Polylactide-Functionalized Polyoxanorbornenes

This paper describes the synthesis of polylactide-functionalized polyoxanorbornenes and their hydrolytic degradation behavior. Macromonomers with one or two exo-PLA chains as well with two endo,exo chains were prepared using tin(II) 2-ethylhexanoate as a catalyst in the presence of mono- or dialcohol derivatives of oxanorbornene. The well-characterized macromonomers were then subjected to ROMP by first, second, and modified second generation Grubbs ruthenium initiators. Investigation of these graft copolymers by SEC and NMR spectroscopy showed the presence of some uncapped PLA homopolymer, formed as a side product during the ROP of lactide. The degradation behavior showed that the presence of PLA homopolymer impurities in the graft copolymers significantly increases the rate of degradation of the final material. Therefore, a convenient procedure of graft copolymers purification to remove PLA homopolymer from the samples was developed. The degradation studies of graft copolymers with the same oxanorbornyl backbone length and different length of PLA grafts indicated that the degradation rate increased with increasing length of PLA grafts. The degradation behavior of material depends also on configuration of PLA side chains on polyoxanorbornene backbone chain. The fastest degradation was observed in the case of graft copolymers with one exo-PLA side chain.

Controlling Network Structure in Degradable Thiol−Acrylate Biomaterials to Tune Mass Loss Behavior

Degradable thiol-acrylate materials were synthesized from the mixed-mode polymerization of a diacrylate poly(ethylene glycol) (PEG) monomer with thiol monomers of varying functionalities to control the final network structure, ultimately influencing the material's degradation behavior and properties. The influence of the concentration of thiol groups and monomer functionality on the mass loss profiles were examined experimentally and theoretically. Mass loss behavior was also predicted for networks with varying extents of cyclization, PEG molecular weight, and backbone chain length distributions. Experimental results indicate that increasing the thiol concentration from 10 to 50 mol % shifted the reverse gelation time from 35 to 8 days and the extent of mass loss at reverse gelation from 75 to 40%. Similarly, decreasing the thiol functionality from 4 to 1 shifted the reverse gelation time from 18 to 8 days and the mass loss extent at reverse gelation from 70 to 45%.

Tensile and energy density properties of 2024, 6013, 8090 and 2091 aircraft aluminum alloy after corrosion exposure

Evaluation was made for the corrosion susceptibility of aircraft structure aluminum alloys 2024 T351, 6013 T6, 8090 T81 and 2091 T84. Tensile and energy density data were obtained. Stereoscopic and metallographic corrosion analysis were made as well. The specimens were pre-corroded using accelerated laboratory corrosion tests or out-door atmospheric conditions before testing. Noticeable decrease of yield and ultimate tensile stress were detected when the specimen surface was corroded. Dramatic volumetric embrittlement was observed even after short exposure times that were not sufficient for the appreciable development of surface corrosion attack. Observed material degradation behavior is attributed to hydrogen penetration and absorption.

The corrosion of Cu-Ni alloy in a chloride solution subjected to periodic voltage modulation: Part I

The influence of full-wave sinusoidal, and positive half-wave and negative half-wave rectified sinusoidal potentials superimposed at three DC levels on a Cu-10Ni (CDA 706) alloy immersed in a 3.3% NaCl solution under nitrogen, as well as air, purge on the material degradation behavior was investigated. The results obtained show that although the material degradation rate is strongly influenced by the choice of the applied DC potential level, the more anodic the DC potential, the greater is the corrosion rate. Evidence of intergranular corrosion and cracking is observed. However, no pitting is observed with alternating voltage (AV) modulation in spite of the presence of chloride anions. The material dissolution rate of the alloy was found to decrease with frequency of the AV signal. The rate of alloy dissolution was found to increase with the AV peak potential, as well as with the DC potential. In general, the DC potential is observed to affect the magnitude of the metal dissolution rate more than the corresponding equivalent AV peak potential. It does not appear that imposition of AV signals alters the basic mechanism of corrosion of cupro-nickel alloys.