Stiffness-toughness balance in PP/EPDM/SiO2 ternary blend-nanocomposites: The role of microstructural evolution

The effect of microstructural evolution with hydrophilic-nanosilica (SiO2) concentration, ranging from 0 to 5 wt%, on mechanical properties and deformation micromechanisms of PP/EPDM/SiO2 (80/20/x) ternary blend-nanocomposites was investigated. Morphological observations revealed that, SiO2 nanoparticles tend to localize either around the dispersed EPDM particles or at the PP/EPDM interface, promoting the formation of three dimentional network-like EPDM/SiO2 composite structures dispersed in the PP matrix, especially at higher SiO2 loadings. This type of dispersion state was further confirmed by the rheological analysis. Synergistic toughening effect of soft EPDM particles and rigid SiO2 particles under Izod impact test was observed in these ternary systems, so that the materials with a better balance of stiffness/toughness were achieved. The results demonstrated that the extent of impact toughness increase is higher, where a large amount of the SiO2 nanoparticles surrounded the EPDM dispersed particles distributed in the PP matrix. This significant increase was attributed to the change in the size of stress concentration region and evolution of stress distribution throughout the material. The failure mechanisms were studied, and the underlying toughening micromechanisms were proposed.

Open hole tensile testing of 3D printed continuous carbon fiber reinforced composites

In this study, the effects of stress concentration on the tensile properties of a 3D printed carbon fiber-nylon composite were investigated. The samples were 3D printed with continuous carbon fiber and chopped fiber reinforced nylon. Samples were manufactured with four different open hole sizes as 3. 175 mm (⅛ in), 6.35 mm (¼ in), 9.25 mm (⅜ in), and 12.7 mm (½ in). Five samples were manufactured for each hole size group. Continuous carbon fibers were printed in the longitudinal direction. Additional reinforcements were placed around the periphery of the open hole. Samples were tested under uniaxial tension. The results were compared with the prediction of fracture mechanics theories namely Average and Point Stress Criteria. The results show that failure was initiated at the stress concentration region but the progression into the hole was prevented with the presence of continuous fiber. The experimental findings show that the samples with larger holes are more sensitive to discontinuity than the ones with smaller holes. The results confirm that 3D printing can be used to strengthen the parts at the discontinuity region to mitigate the effect of stress concentration.

Biomechanical comparison between the custom-made mandibular condyle prosthesis and total temporomandibular joint prosthesis in finite element analysis

Purpose: The purpose of this study was to compare the biomechanical behavior of the custom-made mandibular condyle prosthesis and total TMJ prosthesis. Methods: Three models of one beagle dog, the condyle prosthesis (Model 1, replacing the right condyle only), the TMJ prosthesis (model 2, replacing the whole right TMJ) and the intact TMJ (model 3) were established, and the mechanical responses under muscle forces loading were analyzed using finite element method. Results: Models 1 and 3 had the similar stress distribution on the right disc, which suggested that the condyle prosthesis did not change the disc stress so much when the muscle forces were applied. The stress of the right TMJ prosthesis in Model 2 was larger than both Models 1 and 3, and the stress of the contralateral TMJ reduced by 12% in Model 2. The anterior border of the condyle seemed to be a stress concentration region, not only for the intact condyle, but also for the condyle prosthesis and the total TMJ prosthesis. Conclusions: The total TMJ prosthesis changed the biomechanical balance of the bilateral TMJ. When the condyle prosthesis iss applied, the custom-made profile is recommended.

Corrosion Monitoring Method of Porous Aluminum Alloy Plate Hole Edges Based on Piezoelectric Sensors

Corrosion damage to the aircraft structure can significantly reduce the safety performance and endanger flight safety. Especially when the corrosion occurs in a stress concentration region, such as hole edges, it can easily threaten the entire structure. In this paper, an on-line imaging qualitative monitoring algorithm based on piezoelectric sensors is proposed for detecting hole edge corrosion damage of porous aluminum alloy structures. The normalized amplitude is used to characterize the correlation between the initial Lamb wave signal and the damage signal, which is as an image reconstruction parameter in the algebraic iterative probability reconstruction algorithm. Moreover, a homogenization algorithm is proposed to process the reconstruction results. The experimental results of single hole and double hole corrosion for porous aluminum alloy plate show that the method can effectively achieve the location and quantification of corrosion damage to one and two holes of the porous structure.

Residual stress in underlying silicon at the fixed end of SiO2 microcantilevers — A micro-Raman study

In this work, nature of the residual stress developed in the convex corners created in underlying Si at the fixed end of SiO2 microantilevers (MCs) fabricated by wet chemical etching method was investigated using micro-Raman spectroscopy with visible excitation. It revealed the presence of tensile stress near the sharp edge of the convex corner and is attributed to the localized stress generated in the neighborhood of the discontinuities, acting as stress concentration region. Residual stress estimated by micro-Raman technique across the convex corner was also validated by FEM simulations. Micro-Raman also revealed the presence of tensile stress on the etched Si surface, which is explained on the basis of stress induced by native oxide shells covering the etched features.

Experimental Study on the Fatigue Behavior of Cracked Steel Component Repaired with High Strength Bolt Reinforced Stop-hole and CFRP Patched Stop-hole

<p>The stop-hole method has been used widely to retard the fatigue crack growth of steel component in the field of bridge engineering. However, the component repaired by single stop-hole without any additional reinforcement is liable to crack again because of the drilling defects and new stress concentration region around the hole. In this paper, two kinds of strengthened stop-hole methods, the high strength bolt reinforced stop-hole method and the CFRP patched stop-hole method, were investigated and compared. Finite element analysis was conducted to predict the repair efficiency and investigate the optimal parameters of each method. A total of 12 fatigue damaged specimens were repaired by different ways and tested under fatigue loading subsequently. Experiment results indicate that the fatigue life of specimens repaired by stop-hole is more than 20 times that of the unrepaired specimens. The high strength bolt reinforced stop-hole and CFRP patched stop-hole can extend the fatigue life by 9 and 8 times respectively, compared with the single stop-hole method. Debonding has a decisive effect on the reinforcement effectiveness. In addition, all the three methods studied in this paper can only extend the crack initiation life of the cracked steel component, but can’t affect the crack propagation life.</p>

Three Dimensional Finite Element Analysis of Rolling Contact between Wheel and Rail

The fatigue performance of the rails is affected by many factors, including service conditions, loading, mechanical properties, environment factors, and manufacturing processes. In this paper, the investigation on wheel-rail to identify the initial damages caused by Rolling Contact Fatigue (RCF) cracks and the location that experienced damages is presented. UIC 54kg rail (grade 900A) was used as the model in three dimensional (3D) finite element contact analysis. The fatigue crack growth on wheel-rail was carried out by considering the Hertz contact pressure. The finite element analysis results show that maximum stress concentration zone was between the wheel-rail surface (rail inside curve gauge corner) and it is above the yield stress limit for wheel-rail steel. Fatigue crack propagation within a depth affected stress concentration region was predicted. The stress intensity factors (SIF) for mode I, mode II and mode III fracture were plotted from ANSYS simulation. Three types of fracture modes were affected the UIC54kg rail Steel to fail or develop initial failure when the crack propagation exceeds 5 mm.

Comparison of Stress Intensity Factors of Part Surface Flaws at Stress Concentration in Plate and Pipe Between FE Analysis and Weight Function Approach

Stress intensity factor (SIF) is one of the key parameters in structural integrity assessment. Weight function method has been used in flaw acceptance assessment codes and standards, such as R6 and BS7910, to calculate SIF of a semi-elliptical (part) surface flaw. In this method, stress distribution across the section thickness is described by a polynomial equation, and SIF is estimated using geometry functions fi and stress components σi. The SIF solutions are available for both the deepest and the surface points of part surface flaw in R6 and BS7910. However, a case study from this work shows that the SIF estimation using the current methods are not always conservative when a flaw is at stress concentration, such as weld toe. This results in an optimistic limiting defect sizes and jeopardizes the safety. To account for the effect of stress concentration on SIF, one solution is to use SIF magnification factor and stress concentration factor, but this approach could be overly conservative. Although the original research used power law stress distribution in calculation of SIF, it is not clear whether the developed geometry function factors are suitable for a flaw at steep gradient stress concentration zone. The same question is for the similar SIF solutions of French RCC-MR code, as the model used to derive the SIF does not include stress concentration. This paper briefly reviews the weight function SIF solutions and compares them with the 3D FEA results of surface flaws in plate and pipe with various dimensions and flaw sizes. The guidance is provided on how to use weight function SIF solutions for surface flaws at stress concentration region for structural integrity analysis.

Design and analysis of Micro-Cantilever based Biosensor for Swine flu Detection

Swine flu which comes under the category of influenza is caused by N1H1 virus. This Disease in 2009 was termed as pandemic by WHO (World Health Organisation). It was fast spreading almost all over the world then. It is same as normal Flu and can be prevented by flu shots/vaccines. The real importance of the disease is because , it may cause serious health conditions like Pneumonia, Respiratory asthma, bronchitis different types of mucus line cancers ,unlike normal flu. Sometimes human life can be endangered by post effects of Swine flu. According to a study Infant mortality is because due to lack of detection of diseases. Thus Detection of Swine flu virus, which is cause for infant mortality is important. This can be done using the most trusted form by using MEMS. In this paper the Micro-Cantilever is used as the sensing unit. Using COMSOL 4.3b, we designed rectangular cantilever and also a rectangle with a hole punched forming SCR (Stress Concentration Region) concept, analysed and optimized.

Design and analysis of Micro-Cantilever based Biosensor for Swine flu Detection

Swine flu which comes under the category of influenza is caused by N1H1 virus. This Disease in 2009 was termed as pandemic by WHO (World Health Organisation). It was fast spreading almost all over the world then. It is same as normal Flu and can be prevented by flu shots/vaccines. The real importance of the disease is because , it may cause serious health conditions like Pneumonia, Respiratory asthma, bronchitis different types of mucus line cancers ,unlike normal flu. Sometimes human life can be endangered by post effects of Swine flu. According to a study Infant mortality is because due to lack of detection of diseases. Thus Detection of Swine flu virus, which is cause for infant mortality is important. This can be done using the most trusted form by using MEMS. In this paper the Micro-Cantilever is used as the sensing unit. Using COMSOL 4.3b, we designed rectangular cantilever and also a rectangle with a hole punched forming SCR (Stress Concentration Region) concept, analysed and optimized.