Influence of multi-walled carbon nanotubes (MWCNT) on the static and high-cycle fatigue properties of adhesive joints of 2024-T3 aluminium alloy subjected to peel

U radu se predstavljaju rezultati istraživanja provedenog u svrhu određivanja utjecaja nanofilera od epoksidnih ljepila u obliku višestjenih ugljikovih nanocjevčica - multiwall carbon nanotubes (MWCNT) na zamornu čvrstoću i vijek trajanja do zamora adhezijskih spojeva podvrgnutih ljuštenju. Ugljikove nanocjevčice su sintetizirane s Fe-Co katalizatorima primjenom CVD metode. Razmatrane su tri varijante primijenjenog epoksidnog ljepila, a upotrjebljene su količine od 0.5 wt.%, 1.0 wt.%, 1.5 wt.%. Takvi su sastavi prošli kroz postupak miješanja, osiguravajući odgovarajuću disperziju nanocjevčica. Pripremljeni se sastav koristio za spajanje dva adherenda napravljena od aluminijske legure 2024-T3. Adhezijski spojevi su podvrgnuti visokocikličkim probama čvrstoće i ljuštenja na zamor s brojem ciklusa ograničenim na 2 milijuna. Probe su izvedene na elektromagnetskom induktoru vibracija s frekvencijom rezonancije fleksibilnog adhezivom spojenog elementa od oko 600 Hz. Za svaku varijantu, krivulja zamora i vijek trajanja do zamora određeni su za datu razinu naprezanja. Zahvaljujući dodavanju ugljikovih nanocjevčica epoksidnim ljepilima otkrivena je mogućnost povećanja zamorne čvrstoće za 28.9 % i vijeka trajanja do zamora od oko 477.2 %. Prije proba čvrstoće na zamor provedene su statičke T-peel probe.The paper presents the results of the research undertaken to determine the impact of the epoxy adhesive nanofiller, in the form of multiwall carbon nanotubes (MWCNT), on the fatigue strength and fatigue lifetime of adhesive joints subjected to peel. Carbon nanotubes were synthesized by means of CVD method with Fe-Co catalysts. Three variants of filled epoxy adhesive were considered, the quantity of 0.5 wt.%, 1.0 wt.%, 1.5 wt.% were used. Such compositions went through the process of mixing, ensuring the adequate nanotubes dispersion. The prepared composition was used to join two adherends made of 2024-T3 aluminium alloy. Adhesive joints underwent high-cycle fatigue peel strength tests with the limit number of cycles of 2 million. The tests were carried out on the electromagnetic vibration inductor with the resonance frequency of the flexible adhesive-joined element of about 600 Hz. For each variant, the fatigue curve and fatigue lifetime were determined for a given level of stress. Thanks to adding carbon nanotubes to epoxy adhesives, the possibility of increasing the fatigue strength by 28.9 % and the fatigue lifetime by about 477.2 % was discovered. The fatigue strength tests were preceded by static T-peel tests

THE INFLUENCE OF LAP SIZE ON SHEAR STRENGTH OF ADHESIVE JOINTS

Adhesive joints may be used instead of forced-in joints, welded and riveted joints, soldered and twisted connections. They are characterized by a lot of advantages, thanks to them the adhesive joints are willingly used in manufacturing processes. These advantages include low price of joint, reduction of weight of the final construction, improvement of durability, reliability and quality and improving visual appearance. From this point of view it should be concluded that experimental tests of adhesive joints are grounded. In the paper the results of experimental tests of static shear strength of single-lap joints are presented. These joints are made with two constructive glues. The specimens made from AISI 4130 steel were glued. Their surfaces were prepared in two versions before gluing: grinded with abrasive paper by hand and cleaned by sand-blasting. The results were analyzed from variable size of the lap point of view

Experimental and Numerical Investigation of Impact Resistance of Riveted and RFSSW Stringer-Stiffened Panels in Blunt Impact Tests

Aluminium alloy sheets have come into widespread use in the design of stringer-stiffened aerospace structures. This paper evaluates experimentally and numerically the response of stringer-stiffened Alclad 7075-T6 aluminium alloy panels subjected to impact loading. The aim of the study was to compare the impact resistance of riveted structures with the structures with the impact resistance of structures welded using the refill friction stir spot welding (RFSSW) process, which is a relatively new technique now used to create joints in aircraft structures. The experimental tests were carried out using a drop-weight type impact testing machine. Finite element modelling of stringer-stiffened panels under impact loading was carried out by using the nonlinear finite element-based MSC.Marc + Mentat program. The results of the numerical computations were validated against the experimental data. Studies were also made of the resistance of the joints to failure, the springback response and the stiffness of joints in the conditions of the dynamic impact test

Friction modeling of Al-Mg alloy sheets based on multiple regression analysis and neural networks

This article reports a proposed approach to a frictional resistance description in sheet metal forming processes that enables the determination of the friction coefficient value under a wide range of friction conditions, without performing time-consuming experiments. The motivation for this proposal is the fact that there exists a considerable amount of factors that affect the friction coefficient value and as a result building analytical friction model for specified process conditions is practically impossible. In this proposed approach, a mathematical model of friction behaviour is created using multiple regression analysis and artificial neural networks. The regression analysis was performed using a subroutine in MATLAB programming code and STATISTICA Neural Networks was utilized to build an artificial neural networks model. The effect of different training strategies on the quality of neural networks was studied. As input variables for regression model and training of radial basis function networks, generalized regression neural networks and multilayer networks, the results of strip drawing friction test were utilized. Four kinds of Al-Mg alloy sheets were used as a test material.publishedVersio

Iron Inhibits Respiratory Burst of Peritoneal Phagocytes In Vitro

Objective. This study examines the effects of iron ions Fe3+ on the respiratory burst of phagocytes isolated from peritoneal effluents of continuous ambulatory peritoneal dialysis (CAPD) patients, as an in vitro model of iron overload in end-stage renal disease (ESRD). Material and Methods. Respiratory burst of peritoneal phagocytes was measured by chemiluminescence method. Results. At the highest used concentration of iron ions Fe3+ (100 μM), free radicals production by peritoneal phagocytes was reduced by 90% compared to control. Conclusions. Iron overload may increase the risk of infectious complications in ESRD patients

Peritonitis-induced antitumor activity of peritoneal macrophages from uremic patients.

The macrophages belong to the effector cells of both nonspecific and specific immune response. These cells generally express little cytotoxicity unless activated. The present work was intended to determine if peritoneal macrophages collected from patients on Continuous Ambulatory Peritoneal Dialysis (CAPD) during episodes of peritonitis were active against human tumor cell lines without further in vitro stimulation. We also compared macrophage antitumor potential with effectiveness of drugs used in cancer therapy (taxol and suramin). Conditioned medium (CM) of macrophages collected during inflammation-free periods did not exhibit cytostatic and cytotoxic activity against both tumor (A549 and HTB44) and non-transformed (BEAS-2B and CRL2190) cells. Exposure of tumor cells to CM of macrophages harvested during peritonitis resulted in significant suppression of proliferation, impairment of viability and induction of apoptosis, in contrast to non-transformed cells, which remained unaffected. The efficacy of CM of inflammatory macrophages as an antitumor agent appeared to be comparable to cytostatic and cytotoxic potency of taxol and suramin or, in the case of HTB44 cells, even higher. The results obtained suggest that activated human macrophages might represent a useful tool for cancer immunotherapy

Peritonitis-induced antitumor activity of peritoneal macrophages from uremic patients

The macrophages belong to the effector cells of both nonspecific and specific immune response. These cells generally express little cytotoxicity unless activated. The present work was intended to determine if peritoneal macrophages collected from patients on Continuous Ambulatory Peritoneal Dialysis (CAPD) during episodes of peritonitis were active against human tumor cell lines without further in vitro stimulation. We also compared macrophage antitumor potential with effectiveness of drugs used in cancer therapy (taxol and suramin). Conditioned medium (CM) of macrophages collected during inflammation-free periods did not exhibit cytostatic and cytotoxic activity against both tumor (A549 and HTB44) and non-transformed (BEAS-2B and CRL2190) cells. Exposure of tumor cells to CM of macrophages harvested during peritonitis resulted in significant suppression of proliferation, impairment of viability and induction of apoptosis, in contrast to non-transformed cells, which remained unaffected. The efficacy of CM of inflammatory macrophages as an antitumor agent appeared to be comparable to cytostatic and cytotoxic potency of taxol and suramin or, in the case of HTB44 cells, even higher. The results obtained suggest that activated human macrophages might represent a useful tool for cancer immunotherapy

Small Caliber Bulletproof Test of Warships’ Hulls

The article presents the characteristics of 1.3964 steel and the results of firing a 7.62 mm projectile with a steel core. A simplified Johnson–Cook material model for steel and projectile was used. Then, a FEM (finite element method) simulation was prepared to calibrate the material constants and boundary conditions necessary to be used in simulations of the entire hull model. It was checked how projectile modeling affects the FEM calculation results. After obtaining the simulation results consistent with the experimental results, using the model of a modern minehunter, the resistance of the ship’s hull to penetration by a small-caliber projectile was tested

Wpływ smarowania na właściwości tarciowe blach ze stopu aluminium EN AW-2024-T3

The article presents the results of friction tests conducted on EN AW-2024 Alclad aluminium alloy sheets. The lubrication efficiency of oleic acid, mineral and vegetable oils with the addition of SiO2 and TiO2 nanoparticles was determined using the strip drawing test to assess the friction conditions in the flange area in the deep drawing process. The samples in the form of sheet metal strips were pulled between countersamples with a rounded surface at a speed of 2.5 mm/s. Gear oil and oleic acid demonstrated the lowest value of the coefficient of friction (COF) in the whole range of nominal pressures investigated. The lowest efficiency in reducing the COF was shown by hydraulic oil, olive oil and machine oil. A high content of TiO2 nanoparticles (0.5-0.9%wt%) is beneficial in the friction process involving oleic acid.W artykule przedstawiono wyniki badań tarcia blach ze stopu aluminium EN AW-2024-T3 Alclad. Efektywność smarowania za pomocą kwasu oleinowego, olejów mineralnych oraz roślinnych z dodatkami nanocząstek SiO2 oraz TiO2 została określona za pomocą testu przeciągania blachy używanego do oceny warunków tarcia panujących w kołnierzowej części wytłoczki w procesie głębokiego wytłaczania. Próbki w postaci pasów blachy przeciągano pomiędzy przeciwpróbkami o zaokrąglonej powierzchni (R = 200 mm) z prędkością 2,5 mm/s. Olej przekładniowy oraz kwas oleinowy zapewniły najmniejszą wartość współczynnika tarcia w całym zakresie analizowanych nacisków nominalnych. Najmniejszą efektywność zmniejszania współczynnika tarcia wykazały olej hydrauliczny, oliwa z oliwek oraz olej maszynowy. Najkorzystniejszy efekt zmniejszenia wartości współczynnika tarcia wynikający z dodatku nanocząstek SiO2 jest widoczny dla kwasu oleinowego przy zawartości nanocząstek 0,5% (wagowo). Wysoka zawartość nanocząstek TiO2 (0,5-0,9% wagowo) jest korzystna podczas procesu tarcia z udziałem kwasu oleinowego