Volume 61, Issue 12

In this investigation, the effect of cryogenic treatment (CT) on room temperature mechanical properties was investigated. 10 mm thick AA5083-H321 plates were friction stir welded and the welds were deep treated cryogenically using liquid nitrogen. The effect of CT on the mechanical properties of the welds was investigated by hardness, tensile, and impact tests. Weld microstructures were also examined by light microscopy and scanning electron microscopy. The cryogenic treatment was found to marginally improve the hardness across the weld. The CT was found to exhibit a minimal improvement in both yield and tensile strengths of the base material and the welded joint. However, the percentage elongation was not affected by the CT process. Tensile failures occurred in the weld nugget and thermo-mechanically-affected zone interface for both untreated and treated welds. The impact toughness was found to decrease after the CT, and the effect is more pronounced in the welds than in the base material. The effect of CT on microstructures was not found to be noticeable. On the whole, it is understood that there is a slight increase in strength and hardness and a slight decrease in toughness as a result of cryogenic treatment.

An effective method for evaluating the fatigue strength of thick unidirectional composite laminates of wing spar caps has been presented here. A typical width-tapered bending specimen has been developed for a four-point loading set up. Static and fatigue loading was performed at a load ratio R = ‒1. The complex stress state has been investigated numerically by finite element analysis. Finally, the concept is proven experimentally on specimens made of pultruded fibre rods. The fatigue behavior of the continuously tapered width by water jet cutting has been compared to discrete tapering via rod-drop. The new method enables a screening of material fatigue behavior caused by normal and shear loading.

The focus of the study is on the effect of copper addition on the porosity, microstructure and mechanical properties of hot pressed NiTi and NiTiCu shape memory alloys (SMAs), ignited by means of self-propagating high-temperature synthesis (SHS). Optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometry (EDS), hardness tests and compression tests were applied respectively to determine the microstructure and mechanical behavior of the samples. The experimental results show that the addition of Cu into NiTi SMAs increases porosity and microhardness but also reduces compressive strength.

For the optimal planning of Wöhler tests, DIN 50100 offers tables with different methods, such as the load level method, the pearl-string method and staircase method, to identify the required minimum sample size. Based on this norm, the sampling planning by means of the load level method was optimized in this work. Analytical formulas were developed with statistical methods. These formulas enable a fast estimation of the sample size for arbitrary use cases. Another optimization was the implementation of varying standard deviation within the area of fatigue strength in the load level method corresponding to DIN 50100. This optimization decreases the sample size compared to a constant standard deviation. Both optimizations were implemented via a MATLAB® based tool which also contains the methods of DIN 50100.

The Monte Carlo method enables the statistical simulation of the mechanical properties of groups taken from a given population. In the case of composite pressure vessels used for hydrogen storage, properties like burst strength or fatigue cycle strength are of interest. This paper provides comprehensive information on how populations are generated and how samples can be taken and evaluated; it also explains how to determine the acceptance rate of random samples from simulated populations for passing the approval test “minimum burst pressure”. A word of caution is also expressed regarding the evaluation of acceptance rates from a small sample.

In this study, the eccentric shaft of a 13B MSP (Multi Side Port) single-rotor Wankel test engine was examined. The eccentric shaft was studied in two parts, both through modeling and experimentally. The eccentric shaft was modeled via a workbench module using ANSYS software. Here, the shaft was modeled according to the original dimensions at different speeds ranging from 1000 to 10000 rpm under different operating temperatures (25, 50 and 90 °C). In the analysis, von Mises stress and corresponding deformations were examined under the specified conditions. Afterwards, the stress and deformation of the eccentric shaft were experimentally investigated in engine tests performed at low loads and speeds. The eccentric shaft broke after approximately 200 hours. It was found that broken region was specified to critical points for validity of the applied model used in the current study. Thus, it was shown deformation and stress values can be predicted by numerically modeling the eccentric shaft with the help of ANSYS software in order to determine whether the eccentric shaft can withstand external loading under various conditions.

In this study, the corrosion properties of Ti micro-alloyed AZ91 Mg alloys, having various Fe impurity contents (0.025 to 0.1 wt.˙-%), have been investigated. Microstructural investigations were carried out by using scanning electron microscopy. The corrosion behavior of the alloys was evaluated by means of both immersion (3, 7, 21 days) and electrochemical polarization tests in 3.5 % NaCl solution. Polarization and long-term immersion tests showed that corrosion resistance was significantly increased by the micro-alloying of AZ91 alloy with Ti, even at very high Fe impurity ratios (i.e, 0.1 wt.-% Fe).

Concrete is the most important building material of our century. Concrete, which works under compression, is a brittle material with a low tensile strength. The addition of various types of fibers to concrete increases its ductility. Basically, the use of fibers is intended to increase crack control and ductility. Today, the use of various fibers is becoming widespread. It may be necessary from time to time to reassess and evaluate newly completed reinforced concrete buildings or those buildings still under construction as well as those in existence for years. The concrete strength of a building can be determined by using non-destructive methods or by taking cores. It is an inevitable necessity that the number of cores be limited because taking cores may lead to a weakening of the structural members. The aim of this study is to compare the mechanical properties of concrete with steel fiber, polypropylene fiber and with both in combination and to investigate the effects of using these fibers on the mechanical properties of concrete. Another objective of the study is to compare concrete compressive strength as determined by the destructive method with that determined by a non-destructive method.

Pressure hulls are one of the keys in the design of submarines. In order to improve the accuracy and efficiency of pressure hull structure, methods of optimizing it were studied. In the present study, an overview of the multi-objective optimization of intersecting cross elliptical pressure hulls (ICEPH) with and without the core layer under hydrostatic pressure was investigated in order to maximize buckling load capacity (λ) and minimize the buoyancy factor (B.F) of the ICEPH according to the design requirements. Five models were built, four composite models constructed from boron/epoxy (B(4)/5505) and carbon/epoxy composite (USN-150) with and without core layer. The fifth is a reference metallic model constructed from HY100. Criteria regarding failure for both composite and metal shells are considered as indications of optimization. Both Tsai-Wu and maximum stress failure criteria were employed to check the composite failure. The modeling and the multi-objective optimization were performed using ANSYS parametric design language (APDL) in order to determine mass, critical buckling load, and failure criteria. The results illustrated that carbon fiber-epoxy composite (USN-150) with a core layer is preferred for obtaining minimum weight, with an improvement ratio (I R ) 64.314 % superior to that of a metallic pressure hull. By contrast, (boron/epoxy B(4)/5505) without a core layer is preferred to obtain a maximum buckling load.

The design of electric machines is motivated by electromagnetic and mechanical requirements. The magnetic flux is confined and guided by ferrite cores which consist of coated electrical sheets with a thickness of only a few tenths of a millimeter in order to minimize the eddy current losses. This heterogeneous structure causes preload dependent transversal isotropic material properties which affect the fatigue behavior and structural dynamic behavior of the machine. The material constitutive equations are defined by five parameters which must be derived from experimental investigations with respect to compression in the stacking direction. In this paper, a test procedure is introduced to determine the elastic and torsional stiffness as well as the lateral elongation of the stack depending on its preload.

This paper examines the effects of inoculant type and treatment material quantity on the mechanical and thermal properties of rail vehicle brake discs manufactured from vermicular graphite cast iron/compacted graphite iron (CGI). The in-mold treatment technique was employed in manufacturing the CGI brake discs. The main and interaction effects of inoculant type and treatment material quantity parameters affecting the tensile strength of the CGI brake discs were determined. The results indicate that treatment material quantity has the most significant effect on mechanical properties. Tensile strength was observed to increase as the treatment material quantity increased. The optimum level for manufacturing the CGI brake disc by using the in-mold treatment technique was attained via the combination of SB 5-type inoculant and 625 g treatment material quantity.

The characteristics of wood filler-thermoplastics composites coupled with the incessant order of these products on a daily basis have long been of scholarly interest. This work is aimed at investigating the influence of chemical-modified avocado pear wood filler (APWF) on the mechanical and water absorption behavior of low-density polyethylene (LDPE). The avocado pear wood filler-low density polyethylene (APWF/LDPE) composites were prepared by fresh APWF (UN) modified by the action of sodium hydroxide (NS), sodium hydroxide/acetic acid (AA) and sodium hydroxide/acetic acid/maleate polyethylene (MP), respectively and then merged with a low-density polyethylene (LDPE) matrix by injection molding, respectively. The effect of the filler content on the properties was evaluated. The active groups and morphology of APWF/LDPE composites were studied using a Fourier transform infrared (FTIR) spectrometer and a scanning electron microscope (SEM), respectively. The treated APWF exhibited better mechanical properties and higher water resistance than the UN with a greater improvement for the MP of the APWF/LDPE composite as captured by a FTIR and SEM graph. Consequently, the MP of an APWF/LDPE composite is highly recommended as an application for furniture and finishings.

Due to the importance of high surface quality of machined parts, regarding its functional requirements, it is necessary to determine an appropriate set of grinding parameters. According to the uncertainty of the machining process, the statistical techniques have recently been used to set up an experimental-based model for estimating the performance of machining parameters and optimizing them. The purpose of this study is to demonstrate the modeling and optimization of the grinding process using three approaches. First, multi non-linear regression (MNLR) based on central composite design (CCD) was used to determine the process model. Then the grinding parameters were optimized considering response surface methodology (RSM). Finally, the probabilistic uncertainty analysis was applied by using Monte Carlo simulation as a function of wheel speed and feed rate. The surface roughness value, which was named the response variable, was estimated by fitting the MNLR model with a predicted regression coefficient (R 2 pred ) of 84.69 %. Wheel speed of 4205.6 rpm and feed rate of 2.969 mm × min −1 were calculated as RSM-optimized conditions with a surface roughness of 2.26326 μm. The verification experiments were performed with three replications to verify the predicted surface roughness value obtained with the derived model, and 2.263 ± 2 % μm of surface roughness was calculated using RSM optimized conditions. Monte Carlo simulations were found to be quite effective for identification of the uncertainties in surface roughness that could not be identified by deterministic ways.

The plane-strain fracture toughness test method enables the determination of the plane-strain fracture toughness (K IC ) of metallic materials by tests using a variety of precracked specimens, such as bend, compact tension (CT), arc-shaped, disk-shaped specimens. In this study, to determine the effect of the heat treatment process on the specimen thickness required for a valid plane-strain test in accordance with the ASTM standard, fracture tests are performed by using CT specimens made of AISI 1040 carbon steel. Furthermore, by taking into consideration the effect of residual stress caused by heat treatment in the vicinity of the notch, additional fracture tests are also performed. The specimens are machined from rolled plates in the L-T rolling direction (crack plane is perpendicular to the rolling direction). Having performed experimental analyses, the applicability of the plane-strain fracture toughness tests using CT specimen made of AISI 1040 steel is investigated.