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Polyamide 6 (PA6) is extensively used in many industrials due to its chemical and wear resistance, stiffness, excellent strength properties, low friction, and high melting points. In this study, PA6/nitrile butadiene rubber (NBR)/graphene nanocomposites were fabricated by twin-screw extruder (TSE) and friction stir process (FSP). The novelty of our present work is that the fracture mechanisms and failure analysis of PA6/NBR/graphene nanocomposites were studied by the essential work of fracture (EWF) methodology. The scanning electron microscopy and wide X-ray diffraction were used to study the morphology of TSE and FSP samples. The results illustrated that the higher shear stress in FSP compared to the TSE is the reason for better dispersion of the graphene in the PA6 matrix and smaller size of NBR particles. The smaller size of NBR particles and better distribution of graphene in PA6/NBR blend led to high total work of fracture ( $${w}_{f}$$ ) in the FSP sample compared to the TSE sample. The results of the EWF test showed that the addition of 0.5% (wt) graphene nanoparticles into the PA6/NBR blend in the TSE sample decreased the essential work of fracture ( $${\rm{w}}_{\it{e}}$$ ) from 105.6 N/mm to 87.8 N/mm and increased the non-essential work of fracture (βWp) from 2.76 N/mm2 to 3.9 N/mm2; whereas in FSP sample, $${\rm{w}}_{\it{e}}$$ and βWp increased to 115.58 N/mm and 4.66 N/mm2, respectively.

The friction stir process (FSP) method used to prepare polyamide 6 (PA6)/nitrile-butadiene rubber (NBR) nanocomposites with 1 wt% Graphene nanoparticles. Response surface methodology (RSM) and Box-Behnken design were used to study the effects of four input variables including tool rotational speed (ω), shoulder temperature (T), traverse speed (S), and the number of passes (N) on tensile strength and impact strength of PA6/NBR/Graphene nanocomposite. In order to investigate the dispersion state of Graphene and the morphology of the PA6/NBR blend in the presence of Graphene, wide x-ray patterns (WAX), scanning electron microscopy (SEM) were performed. Furthermore and differential scanning calorimetric (DSC) was used to investigate the thermal properties of PA6/NBR containing 1 wt% Graphene nanoparticles. The results confirmed that at the optimum range of input variables, PA6/NBR/Graphene nanocomposite provided good thermal stability as well as the highest tensile strength, and impact strength. This is caused by the large surface area to volume ratio of the dispersed layered Graphene in PA6/NBR blends. Under optimal conditions of the rotational speed of 1200 rpm, traverse speed of 20 mm/min, shoulder temperature of 125°C, and number pass of 3, the maximum tensile strength and impact strength are 70.4 MPa and 70.3 J/m, respectively.

Thermoplastic elastomer (TPE) based on polyamid6 (PA6) / acrylonitrile-butadiene rubber (NBR) containing 5% wt nanoclay (Closite 30B) have been prepared via friction stir process (FSP). In this study, the essential work of fracture (EWF) approach was employed to investigate the fracture behavior of PA6/NBR nanocomposites. Also, the modulus strength of specimens was modeled by response surface methodology (RSM), considering three input variables including rotational speed (ω), traverse speed (S), and shoulder temperature (T). Thus, a quadratic mathematical model between input variables (ω, S and T) and response (modulus strength) of PA6/NBR/clay nanocomposites was achieved. Moreover, the morphology of the PA6/NBR blends containing 5% wt was investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results show that a sample of PA6/NBR thermoplastic elastomer (TPE) containing 5% wt nanoclay at maximum tensile strength exhibited the maximum specific essential work of fracture (we) and specific non-essential work of fracture (wp). Also, the results of the RSM method demonstrate that the optimum condition of the process was found to be at including rotational speed (ω), traverse speed (S), and shoulder temperature (T) of 1200 rpm, 25mm/min, and 146 ℃, respectively. Thus, under the condition optimum, maximum modulus strength of 658 MPa was obtained.

Thermoplastic elastomer of PA6/NBR reinforced by various nanoparticles have wide application in many industries. The properties of these materials depend on PA6, NBR, and nanoparticle amount and characteristics. In this study, the simultaneous effect of NBR and graphene nanoparticle content on mechanical, thermal properties, and morphology of PA6/NBR/Graphene nanocomposites investigated by Central Composite Design (CCD). Thermal properties and morphology of PA6/NBR/Graphene nanocomposites were investigated by Differential Scanning Calorimetry (DSC), X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). The results indicate that a small percentage of error between predicted values of mechanical properties and experimental values was achieved. An increase in graphene content have a positive impact on the tensile strength but increasing the NBR phase has the opposite effect. A maximum tensile strength of 35.3 MPa for PA6/NBR/Graphene nanocomposites was obtained at the NBR and graphene content of 20 %wt and 1.5 %wt, respectively. The thermal behavior of the PA6/NBR blend improved with addition graphene. With the addition of 1.5 % graphene content to PA6/NBR blend, the crystallization temperature and melting temperature increased from 192.1 to 196.2 °C and 221.1 to 223.4 °C, respectively.

The object of this paper is to study the effect of different levels of halloysite nanotubes (HNTs) loading on tensile strength and impact strength of PP/NBR/HNT nanocomposite in presence of PP-g-MA as compatibilizer. Samples containing 20 wt% of NBR, 1, 3, and 5 wt% of HNTs and 10 wt% of PP-g-MA were produced using counter-rotating twin-screw extruder. HNTs enhanced both of the mechanical properties. At all levels of loading, tensile strength plot showed an ascending trend, however in case of impact strength, the optimum level of HNTs was achieved at 3 wt%. Scanning electron microscopy was utilized to figure out the effect of HNTs loading on the way the elastomer phase dispersed into the continuous phase or the matrix.

Polyamide 6 (PA6)/nitrile butadiene rubber (NBR) thermoplastic elastomers (TPEs) reinforced with graphene oxide were compounded by a two-step melt mixing process via an internal mixer. The effect of graphene oxide on tensile and impact strength was investigated. Samples containing 30 wt% of NBR, 0.5, 1.25, and 2 wt% of graphene oxide were produced. Increasing the graphene oxide content from 0.5 wt% to 2 wt%, increased the tensile strength from 63.6 MPa to 69.3 MPa, whereas impact strength decreased from 78.1 MPa to 75.3 MPa when graphene oxide content increased. The morphology study of prepared nanocomposites with scanning electron microscopy (SEM) shows that the size of NBR droplets in TPE nanocomposites reduces by adding of graphene oxide into the PA6 phase.

In deep drawing process, excessive mass flow causes wrinkling and insufficient mass flow causes fracture. Blank holder has direct influence on mass flow into die cavity. In this study, the effect of pulsating blank holder by using a new mechanical system has been investigated for improving the formability of aluminum alloy. Also, this paper presents a systematic methodology for developing second-order statistical model to show the relationship between drawing depth and input variables (frequency of blank holder, amplitude of blank holder movement, and velocity of punch movement). The obtained model was used to analyze the effect of input parameters on performance of pulsating blank holder. The results show that the pulsating blank holder in comparison with static one can increase significantly the limiting drawing ratio of deep drawing process about 11.53%. The optimized drawing depth value is subsequently obtained from the mathematical model.

Thermoplastic elastomeric nanocomposites due to their excellent mechanical, thermal, and chemical properties have a wide application in airplane, shipbuilding, and automotive industries and medical apparatus. Friction stir processing (FSP) is a novel technique for the fabrication of composites, nanocomposites and microstructural modifications. In this paper, polypropylene/ethylene–propylene–diene monomer (PP/EPDM) nanocomposite with 5 wt% nanoclay are fabricated by FSP to determine the effect of process parameters such as tool rotational speed, traverse speed, shoulder temperature, and number of passes on total work of fracture of this nanocomposite. Response surface methodology (RSM) and Box–Behnken design were used to develop a mathematical model relating the process parameters to the total work of fracture. The results show that the total work of fracture increased with increasing the rotational speed and number of passes and decreasing the shoulder temperature. A maximum total work of fracture of 50.3 N/mm was obtained at traverse speed of 42 mm/min when other parameters were at their center level. The maximum total work of fracture of 61.8 N/mm is achieved at rotational speed of 1,200 rpm, traverse speed of 40 mm/min, shoulder temperature of 100°C, and number of passes of 3. POLYM. COMPOS., 2016. © 2016 Society of Plastics Engineers

In this article, effects of friction stir processing parameters such as tool rotational speed, traverse speed, shoulder temperature, and number of passes on tensile modulus and impact strength of polypropylene/ethylene-propylene diene monomer/clay nanocomposite has been investigated. The Box–Behnken design with four factors at three levels was used for design of experiments. The response surface methodology was employed to develop models capable of predicting the effect of input variable on responses. A multi-layer artificial neural network with back propagation algorithm and 4 – 8 – 10 – 2 topology was also selected for modeling. A set of data on friction stir parameters and experimental results of the mechanical properties were used to train and test the artificial neural network. POLYM. COMPOS., 2016. © 2016 Society of Plastics Engineers

Nanocomposites-based on polypropylene (PP), ethylene-propylene diene monomer (EPDM) and Cloisite 15A have wide applications in automotive and aerospace industries and medical apparatus due to their excellent mechanical, thermal and chemical properties. In this study, a nanocomposite of PP/EPDM/nanoclay containing PP (77 wt%), EPDM (20 wt%) and nanoclay (3 wt%) was fabricated by friction stir processing (FSP) method. X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry and tensile testing were performed to determine the morphology and tensile properties of this nanocomposite. The Box-Behnken design was applied to investigate the effect of the process parameters such as tool rotational speed, traverse speed and shoulder temperature on the tensile properties of the nanocomposite. The results showed that the tensile strength increased from 15.8 to 18.2 MPa with increasing the tool rotational speed and shoulder temperature while the elongation-at-break dropped from 46 to 22 %. A maximum tensile strength of 17.6 MPa and a minimum elongation-at-break of 26 % were obtained at the traverse speed of 40 mm/min when the rotational speed and shoulder temperature were at the central levels themselves. The prediction models showed that when the tool rotational speed, traverse speed and shoulder temperature were set, in the given order, as 1200 rpm, 45.65 mm/min and 113.65 °C, a simultaneous maximization of tensile strength of 16.03 MPa and elongation-at-break of 46.41 % was obtained.

Welding as a fabrication process can be used to join materials, including composite and nanocomposites and laser welding process due to its advantages has found wide applications in this field. Its process parameters can play a significant role in determining the weld strength of laser-welded joints in polypropylene/clay nanocomposites. In this study, the effect of laser welding parameters, such as laser power, welding speed and focal position along with the clay content in a polypropylene/clay nanocomposite on weld strength were determined using response surface methodology. This methodology was applied for developing a mathematical model which can predict the main effects of the above parameters and their impacts on tensile strength of butt-welded laser joints in 2-mm thick polypropylene/clay nanocomposite sheets. The analysis of variance was performed to check the adequacy of the developed model. A comparison was also made between the predicted and actual results. The results showed that weld strength decreased when clay content was increased from 0 to 6 %, but welding speed increased from 30 to 60 mm/s. The above parameters were also optimized to achieve a high strength welded joint.

In this paper, polypropylene-clay nanocomposite sheets of 2 mm thickness with 0 wt%, 3 wt% and 5 wt% nanoclay are butt welded using a CO2 laser to determine the effect of clay content and laser process parameters on weld tensile strength. For this purpose, Taguchi parametric design and optimization method was used to design experiments and develop a model to predict weld tensile strength as a function of clay content and laser process parameters such as laser power, welding speed and focal position. The adequacy of the model was checked using analysis of variance and by conducting extra confirmation tests. Using Taguchi optimization approach, the optimum levels of parameters were determined. The results indicated that an increase in clay content and welding speed decreased the weld strength, whereas increasing laser power increased weld strength. Furthermore, increase in focal position showed an increasing and then a decreasing effect on weld strength.

Laser welding of plastic materials has a wide range of applications in the packaging, medical, electronics and automobile industries provided it can predict high quality welds compared with other joining methods. Laser welding process parameters can affect the quality of welds. In this paper, Artificial Neural Network (ANN) is used to model the effects of laser power, welding speed, clamp pressure and stand-off distance on weld lap-shear strength in laser transmission welding (LTW) of acrylic (polymathy methacrylate). A set of experimental data on diode laser weld lap-shear strengths was used to train and test the ANN from which the neurons relations were gradually extracted to develop a model. The developed ANN model can be used for the analysis and prediction of the complex relationships between the above mentioned process parameters and weld lap-shear strength. The results indicated that increase in laser power and clamp pressure increases the weld lap-shear strength whereas welding speed and stand off distance had a decreasing affect on shear strength at high value.

OBJECTIVE: Despite research in Western countries finding high levels of psychological morbidity in medical students and doctors, little is known about difficulties faced by medical staff in the Middle East. The aim of the present study was to assess emotional disturbance and interpersonal attitudes in a representative sample of Iranian medical students and practitioners. METHOD: A total of 82 medical students, 92 interns and 89 general practitioners (GPs) participated in the study. Participants rated the 28-item version of the General Health Questionnaire (GHQ-28) and a measure of interpersonal attitudes. RESULTS: A total of 44% of participants scored above the threshold of the GHQ-28, indicating probable psychiatric disorder. The GHQ-28 scores were higher in students than interns or GPs and in women compared with men. Medical students and doctors had high levels of indifference and cynicism. CONCLUSIONS: This study suggests that psychological morbidity was common in Iranian medical students and practitioners, particularly women. Women were at particular risk. A high prevalence of emotional disturbance among health care practitioners is likely to compound existing problems of health care provision.

In recent years, polymer – based nanocomposites have found wide applications in various industries. Polypropylene / ethylene – propylene - diene monomer /Nanoclay (PP/EPDM/Nanoclay) nanocomposite is one of these materials that has many applications in automotive and aircraft industries. Welding as a fabrication process has attracted the attention of researchers for joining these materials. Among welding processes, laser welding because of its advantages can be a choice for joining of PP/EPDM/Nanoclay nanocomposites. In this paper, the effect of CO2 laser power, scan velocity, stand-off distance and clay content on impact strength of butt-welded PP/EPDM/Nanoclay 3.2 mm sheets is investigated. The response surface methodology (RSM) is used to develop a statistical model relating the above parameters to the impact strength of the weld joint. The results indicated that increase in clay content and scan velocity decreased the impact strength whereas stand-off distance increased it. The maximum impact strength of 70 J/m is achieved at laser power of about 103 W, velocity of 400 mm.min-1 , stand-off-distance 8 mm and clay content of about 1.3% wt.