Characterising and representing small crack growth in an additive manufactured titanium alloy

The purpose of the research is to apply the modified Hartman-Schijve equation for predicting small crack growth rate in an additive manufactured titanium Ti-6Al-4V. Material constants in the equation were determined by long crack test data, and the threshold value of the stress intensity factor range was set to a small value. A small fatigue crack test was conducted to validate the fitted equation. Predicted fatigue life of another specimen configuration under bending load agreed well with the test result. The work shows that it may be possible to represent both small and long crack growth rates by the modified Hartman-Schijve equation with its material constants being determined by long crack test

PENERAPAN TEKNIK EMPTY CHAIR UNTUK MENGURANGI TINGKAT KECEMASAN MENGHADAPI UJIAN NASIONAL PADA SISWA KELAS IX DI SMP NEGERI 17 MAKASSAR.

Muhammad Shamir Maulana 2019. Pengaruh Teknik Empty Chair Dalam Mengatasi Tingkat Kecemasan Siswa Menghadapi Ujian Nasional di SMP Negeri 17 Makassar. Dibimbing oleh Prof. Syamsul Bachri Thalib, M.Si dan Dr.Abdullah Pandang M.Pd Jurusan Psikologi Pendidikan dan Bimbingan Fakultas Ilmu Pendidikan Universitas Negeri Makassar. Permasalahan dalam penelitian ini yaitu tingginya tingkat kecemasan siswa saat menghadapi ujian nasional. Penelitian ini bertujuan untuk mengetahui 1) gambaran tingkat kecemasan siswa menghadapi ujian nasional di SMP Negeri 17 Makassar. 2) gambaran penerapan teknik empty chair di SMP Negeri 17 Makassar. 3) teknik empty chair dapat mengurangi kecemasan siswa menghadapi ujian nasional di SMP Negeri 17 Makassar. Penelitian ini menggunakan pendekatan kuantitatif dengan model Quasi experimental design. Desain Eksperimen yang digunakan adalah nonequivalent control group design. Populasi penelitian ini adalah siswa kelas X sebanyak 55 siswa dan sampel penelitian sebesar 20 siswa yang terbagi menjadi kelompok eksperimen dan kelompok kontrol yang masing-masing berjumlah 10 siswa. Penarikan sampel dengan teknik proportional random sampling. Pengumpulan data dengan menggunakan instrumen skala kecemasan belajar dan pedoman observasi. Analisis data menggunakan analisis statistik deskriptif dan analisis parametrik, yaitu uji t. Hasil penelitian menunjukkan bahwa: 1) Tingkat kecemasan siswa dalam menghadapi ujian nasional saat pretest pada kelompok eksperimen dan kontrol berada pada kategori tinggi. Pada saat posttest, tingkat kecemasan dalam menghadapi ujian nasional siswa kelompok eksperimen mengalami perubahan ke kategori rendah dan pada kelompok kontrol tetap berada pada kategori tinggi. 2) Pelaksanaan teknik empty chair dilaksanakan sesuai dengan prosedur yang sudah dirancang melalui 4 tahapan yaitu rasional treatment, identifikasi sumber masalah, permainan top dan under dog, dan evaluasi. 3) Ada perbedaan tingkat kecemasan siswa dalam menghadapi ujian nasional pada kelompok yang diberikan perlakuan dan pada kelompok yang tidak diberikan perlakuan berupa teknik empty chair. Artinya, penerapan teknik empty chair dapat mengurangi tingkat kecemasan siswa dalam menghadapi ujian nasional secara signifikan di SMP Negeri 17 Makassar. Kata Kunci: Teknik empty chair, Kecemasan Menghadapi Ujian Nasional

Predicting the Effect of Surface Waviness on Fatigue Life of a Wire + Arc Additive Manufactured Ti-6Al-4V Alloy

This paper reports the effect of as-deposited surface conditions on the fatigue strength of an additively manufactured titanium alloy, Ti-6Al-4V (WAAM Ti64). First, the local stress concentration caused by the surface waviness was quantified using a metrology technique and computer modelling. Fatigue tests were conducted under bending loads at a cyclic load ratio of 0.1. The applicability of two predictive methods was the focus of this study. The traditional notch stress method was unable to predict the correct S–N curve trend slope, which could be attributed to the early crack initiation from the troughs on the as-built surface, with crack propagation being the dominant failure mechanism. By treating the troughs as small cracks, the fracture mechanics approach delivered good predictions at every applied stress level. Surface machining and polishing may not always be practical or required; it depends on the applications and service load levels. This research demonstrated that the fracture mechanics approach can be used for predicting the fatigue life of WAAM titanium alloys in as-built conditions and, hence, can be a tool for decision making on the level of surface machining

Investigation of Permeability Deformation of Class G Cement During Acidizing Treatment

Class G cement is widely used in oil and gas industry for well cementing. When the well cannot produce the hydrocarbon as per demand due to positive skin, the well stimulation is carried out. One of the popular well stimulation is acidizing treatment. Previous studies have shown that acidizing treatment was affected the cementing of the wellbore which led to the zonal isolation problem. Even though the main purpose of applying the acidizing treatment is to enhance or improve the productivity of producing hydrocarbon unfortunately it also gives the bad impact to the oil and gas industry as well. The objective of this study is to investigate the permeability deformation of Class G cement during acidizing treatment. Throughout the project, a comparison study between before and after the analysis was carried out. The aims of analysis are to find out the mass loss and also to investigate the permeability deformation upon acid stimulation. The first step was to cure the cement slurries under condition of 3000 Psia and 90°C based on average well condition in Malay basin for eight (8) hours. Then, the samples were immersed in three (3) different concentrations of hydrochloric acid (HCL) / hydrofluoric (HF) acid solution or known as mud acid for 40 minutes

Fatigue life assessment of offshore wind support structures in the presence of corrosion pits

Offshore wind turbine support structures, which connect the wind turbine transition piece and/or tower to the seabed, are located below the sea level and are in direct contact with seawater during the entire lifespan; therefore, they are highly susceptible to corrosion damage and cracking. In particular, the pitting corrosion is very crucial in these support structures, as it leads to local stress concentrations and thus affects the fatigue life. Although corrosion protection mechanisms are commonly implemented in offshore wind turbines, they have a finite life and therefore corrosion damage cannot be completely avoided during the entire life cycle, and this can lead to pitting corrosion on the steel surface. This paper aims to investigate the impact of pitting corrosion on fatigue durability of steel structures by performing tests on lab-scale coupons, made of S355 structural steel which is widely employed in fabrication of offshore wind support structures. For this purpose, cross-weld uniaxial samples were initially exposed to seawater for different time durations and then tested under cyclic loading condition. Furthermore, the durability analysis of corroded samples was carried out using a modified NASGRO equation. The results show that the pitting corrosion significantly reduces the fatigue life, and its level of life reduction is strongly dependent on the seawater exposure time. Moreover, the results show that employment of a linear trend for lower stress ranges would result in significant underprediction of the fatigue life, hence over-conservatism in the design life, at longer seawater exposure times.Engineering and Physical Sciences Research Council (EPSRC): EP/S000747/

Interrupted fatigue testing with periodic tomography to monitor porosity defects in wire + arc additive manufactured Ti-6Al-4V

Porosity defects remain a challenge to the structural integrity of additive manufactured materials, particularly for parts under fatigue loading applications. Although the wire + arc additive manufactured Ti-6Al-4 V builds are typically fully dense, occurrences of isolated pores may not be completely avoided due to feedstock contamination. This study used contaminated wires to build the gauge section of fatigue specimens to purposely introduce spherical gas pores in the size range of 120–250 micrometres. Changes in the defect morphology were monitored via interrupted fatigue testing with periodic X-ray computed tomography (CT) scanning. Prior to specimen failure, the near surface pores grew by approximately a factor of 2 and tortuous fatigue cracks were initiated and propagated towards the nearest free surface. Elastic-plastic finite element analysis showed cyclic plastic deformation at the pore root as a result of stress concentration; consequently for an applied tension-tension cyclic stress (stress ratio 0.1), the local stress at the pore root became a tension-compression nature (local stress ratio −1.0). Fatigue life was predicted using the notch fatigue approach and validated with experimental test results.</p

i-Clo smart dryer closet / Siti Nur Ezzaty Kamar Baharin...[et al.]

i-CIo Smart Dryer Closet will get your day become easy and efficient. I-CIo is a concept of simplify your day life. Nowadays, there are various innovations carried out with existing product. It produces billion throughout the world and still growing from days to days. Our I-CIo product is also among the products that we innovate from existing product in market. We had seen to the areas and other industrial in order to gain inspiration for the concept and come out with new innovations. Always we challenge ourselves and question conventional products or production process. After we go through of all those processes, we have come out with the idea for our new product which is I-CIo Smart Dryer Closet. We introduce our latest product where we are innovating our product by putting a temperature controller, timer controller in order to save time and effort by hanger your clothes into the dryer closet and allow it to dry by setting the temperature and timer controller, supportive fan in order to reduce the dampness on the closet. This dryer is also designed to prevent creasing so that it makes the clothes are so much easier to iron. Besides that, I-CIo can solve the problem of having a tidy home especially for high rise building such as apartment, condominium and others. With the size of I-CIo that we have designed, it will suit for group of family who have limited space in their home and want a tidy home. People are also does not need to be worry about the weather because it is really does not a matter whether it going to be a rainy day or not. When you have our dryer closet, you will have warm and dry clothes all years round. The price of our dryer closet is set at a level to become more affordable to our target customer We are also ISO9002:2000 certified company. Furthermore, we have Product Liability Insurance for all items; it's a double guarantee for customers together with our reliable quality

A review of LTT welding alloys for structural steels : design, application and results

A great deal of effort goes into production of modern steel for structural applications. The structural integrity of the steel becomes compromised when it is welded to form engineering components. The structural capacity of the steel joints is further reduced if the joint is to serve in a fluctuating stress environment. This is because, the fatigue strength (FS) of the steel structure is now shifted to the welded joints. One of the major factors that deteriorate the FS of welded joints is tensile residual stress (TRS). There have been efforts in the last two decades to develop welding alloys capable of mitigating TRS in welded joints based on the phase-transformation of austenite (γ) to martensite (ά). This paper reviews the design, application and results of these alloys often referred to as Low Transformation Temperature (LTT) welding alloys. It also presented the factors affecting them and areas where performance data are lacking

Energy Distribution in f(R) Gravity

The well-known energy problem is discussed in f(R) theory of gravity. We use the generalized Landau-Lifshitz energy-momentum complex in the framework of metric f(R) gravity to evaluate the energy density of plane symmetric solutions for some general f(R) models. In particular, this quantity is found for some popular choices of f(R) models. The constant scalar curvature condition and the stability condition for these models are also discussed. Further, we investigate the energy distribution of cosmic string spacetime.Comment: 15 pages, accepted for publication in Gen. Relativ. & Gra