Development of a fretting-fatigue mapping concept: The effect of material properties and surface treatments

Fretting-fatigue induced by combined localized cyclic contact motion and external bulk fatigue loadings may result in premature and dramatic failure of the contacting components. Depending on fretting and fatigue loading conditions, crack nucleation and possibly crack propagation can be activated. This paper proposes a procedure for estimating these two damage thresholds. The crack nucleation boundary is formalized by applying the Crossland high cycle fatigue criterion, taking into account the stress gradient and the ensuing #size##effect#. The prediction of the crack propagation condition is formalized using a short crack arrest description. Applied to an AISI 1034 steel, this methodology allows the development of an original material response fretting-fatigue map (FFM). The impact of material properties and surface treatments is investigated

Sliding wear analysis of cobalt based alloys in nuclear reactor conditions

The study of the wear behaviour of cobalt based alloys in nuclear reactor environmental conditions is the focus of this work. The alloys are used in components within reactors due to their excellent wear and corrosion resistance and their high hardness in the high pressure and temperature water facing environment. In the nuclear reactor core, cobalt is irradiated producing a highly penetrative gamma emitting isotope, cobalt 60 from stable cobalt 59. Wear of the cobalt alloys, producing wear debris, exacerbates this problem as it may be transported and deposited at various locations throughout the primary loop increasing the potential of radiation exposure. Removing this problem will require the removal of cobalt from the system. In order for suitable replacement materials to be identified, a better understanding of the behaviour of these alloys in the prototypical working conditions must be obtained. This work focuses on two cobalt based alloys used in the ball and race components of rolling element bearings in the reactor core, Stellite 20 and Haynes 25, respectively. The sliding wear behaviour of the alloys in an environment designed to replicate reactor conditions is examined using a bespoke pin on disc tribometer. Wear measurement and microstructural and compositional analysis of the samples tested over a range of conditions are presented and discussed. Concurrent to the experimental work is the development of a wear prediction model using a semi analytical method. The model employs Archard’s wear law as the method of predicting wear using data obtained through experimentation. The accuracy of the semi analytical model is limited however it does give a good estimation for maximum wear depth of the test specimens

Pengembangan E-Modul IPA Berbasis Question Prompt Scaffolding Tema Tekanan Hara Pada Si Hijau Untuk Menumbuhkan Kemampuan Argumentasi Siswa Kelas VIII

The ability to argue well is one of the important requirements in science learning. However, learning that aims to develop students' argumentation skills has not been implemented properly. One solution is to provide learning materials that contain indicators of argumentation skills. These indicators will be presented in the form of an E-Module based on Question Prompt Scaffolding. The purpose of this research and development was to test the validity and readability of the E-Module. This E-Module focuses on the theme of Nutrient Pressure on Green Plants with the aim of improving the argumentation skills of eighth-grade students. The research method used is Research and Development (R&D). The Research and Development (R&D) model is based on the ADDIE model (Analyze, Design, Development, Implementation, Evaluation). Various instruments were used in this study, including a validation questionnaire evaluated by three experts. These experts included subject matter experts, media experts, and science teachers. Additionally, a readability questionnaire was used to measure the readability of the E-Module. The validation results showed that the E-Module achieved an average score of 86% and fell into the “Highly Valid” category. This assessment was based on the subject matter expert's score of 82%, the media expert's score of 91%, and the science teacher's score of 86%. The readability of the E-Module was determined based on students' responses and achieved a score of 94%, categorized as “Very Good.” This proves that the Science E-Module based on Question Prompt Scaffolding with the theme of Nutrient Pressure on Green Plants is considered valid by all validators.Kemampuan mengemukakan argumen secara jelas dan meyakinkan menjadi salah satu unsur krusial dalam pembelajaran Ilmu Pengetahuan Alam (IPA). Namun, proses pembelajaran yang bertujuan mengembangkan keterampilan tersebut masih belum terlaksana secara maksimal. Salah satu solusi yang dapat ditempuh adalah menyediakan bahan ajar yang memuat indikator keterampilan berargumen, seperti melalui E-Modul berbasis Question Prompt Scaffolding. Penelitian ini bertujuan untuk menilai validitas dan keterbacaan E-Modul bertema "Tekanan Hara pada si Hijau", yang dirancang untuk meningkatkan kemampuan argumentatif siswa kelas VIII. Pendekatan yang digunakan adalah metode Research and Development (R&D) dengan model ADDIE, yang terdiri dari tahap Analyze, Design, Development, Implementation, dan Evaluation. Instrumen yang digunakan meliputi angket validasi dari tiga pakar, yaitu ahli materi, ahli media, dan guru IPA, serta angket keterbacaan untuk siswa. Hasil validasi menunjukkan bahwa E-Modul ini memperoleh skor rata-rata 86%, masuk dalam kategori “Sangat Valid”. Secara rinci, ahli materi memberikan penilaian sebesar 82%, ahli media 91%, dan guru IPA 86%. Sementara itu, tingkat keterbacaan oleh siswa mencapai 94%, yang diklasifikasikan sebagai “Sangat Baik”. Temuan ini membuktikan bahwa E-Modul IPA berbasis Question Prompt Scaffolding dengan tema "Tekanan Hara pada si Hijau" dinilai valid oleh seluruh ahli yang terliba

Constraints on the χ_(c1) versus χ_(c2) polarizations in proton-proton collisions at √s = 8 TeV

The polarizations of promptly produced χ_(c1) and χ_(c2) mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at √s=8  TeV. The χ_c states are reconstructed via their radiative decays χ_c → J/ψγ, with the photons being measured through conversions to e⁺e⁻, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χ_(c2) to χ_(c1) yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ → μ⁺μ⁻ decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum