A Nonlocal Strain Gradient Approach for Out-of-Plane Vibration of Axially Moving Functionally Graded Nanoplates in a Hygrothermal Environment

Vibration analyses on axially moving functionally graded nanoplates exposed to hygrothermal environments are presented. The theoretical model of the nanoplate is described via the Kirchhoff plate theory in conjunction with the concept of the physical neutral layer. By employing the nonlocal strain gradient theory, the governing equation of motion is derived based on Hamilton’s principle. The composite beam function method, as well as the complex modal approach, is utilized to obtain the vibration frequencies of axially moving functionally graded nanoplates. Some benchmark results related to the effects of temperature changing, moisture concentration, axial speed, aspect ratio, nonlocal parameter, and the material characteristic scale parameter on the stiffness of axially moving functionally graded nanoplates are obtained. The results reveal that with increasing the nonlocal parameter, gradient index, temperature changing, moisture concentration, and axial speed, the vibration frequencies decrease. The frequencies increase while increasing the material characteristic scale parameter and aspect ratio. Moreover, there is an interaction between the nonlocal parameter and material characteristic scale parameter, influencing and restricting each other.

Brittle material strength and fracture toughness estimation from four-point bending test

The failure stress under four-point bending cannot be considered as an intrinsic material property because of the well-known size effect of increasing maximum flexural stress with decreasing specimen size. In this work, four-point bending tests are analyzed with the coupled criterion for different sample sizes. The maximum flexural stress only tends towards the material tensile strength provided the specimen height is large enough as compared to the material characteristic length. In that case, failure is mainly driven by a stress criterion. Failure of smaller specimens is driven both by energy and stress conditions, thus depending on the material tensile strength and fracture toughness. Regardless of the material mechanical properties, we show that the variation of the ratio of maximum flexural stress to strength as a function of the ratio of specimen height to material characteristic length follows a master curve, for which we propose an analytical expression. Based on this relation, we propose a procedure for the post-processing of four-point bending tests that allows determining both the material tensile strength and fracture toughness. The procedure is illustrated based on four-point bending experiments on three gypsum at different porosity fractions.

Free Vibration of Axially Moving Functionally Graded Nanoplates Based on the Nonlocal Strain Gradient Theory

Using the nonlocal strain gradient theory, we explore vibration behaviours of initially bidirectional tensioned functionally graded nanoplates with axial speed. The governing equation of motion can be obtained based on the differential type of nonlocal strain gradient constitutive relation, which characters the dynamics of nanostructures containing kinematic relation. The simply supported boundary constraints on four sides are considered and subsequently the numerical results are determined. It shows that natural frequencies of axially moving nanoplates decrease when increasing the axial speed and the nonlocal parameter. Hence the nonlocal and kinematic factors cause the natural frequencies to decrease or, weaken the equivalent bending rigidity. On the other hand, natural frequencies increase with an increase in the axial tension and material characteristic scale. Hence the strain gradient and tensile stress factors cause the natural frequencies to increase or, strengthen the equivalent bending rigidity. In addition, the natural frequencies get higher with a larger aspect ratio of the functionally graded nanoplate. The larger one between the nonlocal parameter and the material characteristic scale plays a dominant role in the softening and stiffening mechanisms of the nonlocal strain gradient effect. In case of the same magnitude of the nonlocal parameter and the material characteristic scale, the softening and hardening phenomena disappear. The equivalent bending rigidity neither increases nor decreases in such a situation, and its value degenerates to the classical one.

Proposal of Simulation Materials Test Technique and Their Constitutive Equations for Structural Tests and Analyses Simulating Severe Accident Conditions

Nuclear structure’s integrity must be confirmed under severe accident conditions. However, performing structure tests using actual steels is very difficult and expensive. Therefore, the authors conducted structure tests using the lead alloy to evaluate the structure integrity under severe accident conditions. Because the strength of the lead alloy is considerably less than that of actual steels, structure tests can be conducted under low-pressure, low-temperature conditions. To quantitatively correlate the structural response of the lead alloy to that of actual steels, finite-element analyses (FEAs) must be performed. Because the inelastic constitutive equations, namely, inelastic stress–strain relationship equation, creep rupture equation, and creep strain equation, are required to perform the inelastic FEA, the authors introduced material tests using the lead alloy and, subsequently, proposed the inelastic constitutive equations based on the material test results in a previously conducted PVP conference. However, the proposed inelastic constitutive equations could not successfully express the material characteristic of the lead alloy because of large variations observed in the material tests of the lead alloy. Furthermore, the authors observed that the material characteristic of the lead alloy could be stabilized by aging. In this study, we propose the improved inelastic constitutive equations of the lead alloy on the basis of test results newly obtained from a series of material test performed using aged alloy.

Deep Disadvantage

Arguments in favor of a social adversity or rotten social background defense are substantially stronger than those against. People disagree in principle whether judges should, in appropriate cases, mitigate the severity of sentences to take account of material differences in offenders’ circumstances and characteristics. Many believe that a deeply disadvantaged background is a material characteristic. Unfortunately, informal mitigation of punishments is not enough. The severity and rigidity of American sentencing laws often deny judges the necessary authority. The moral challenges presented by deeply disadvantaged offenders cannot adequately be addressed without creation of a social adversity defense.

Characteristics of selected measures of stress triaxiality near the crack tip for 145Cr6 steel - 3D issues for stationary cracks

In the paper the numerical analysis of the stress fields for 145Cr6 steel, near crack tip is presented, based on three-dimensional finite element method (FEM) analysis. The FEM analysis is focused on SEN(B) specimens with relative crack length a/W ≈ 0.30. In addition to the presentation of the normal components of the stress tensor, the paper presents selected measures of stress triaxiality parameters, measured for the value of the J-integral, corresponding to the experimentally determined fracture toughness, denoted as JIC, which is considered to be a material constant or material characteristic [1, 2]. Presented topic is a continuation of papers [3, 4],whichwere based on experimental analysis, presented in [5].

Manufacture material characteristic analysis of original and alternative auto parts. Case Study: Brake Disc

All powered vehicles have a braking system adopted according to the type of vehicle and work for which they are designed. In Ecuador, there is a great variety of auto parts that are proposed as alternative replacement, varying in cost and quality. This research aims to quantitatively analyze the characteristics of the brake disc material between original and alternate auto parts. This research analyzes three brake disc samples (A, B, C) from different manufacturing sources, using the ASTM E415-08 spectrometry test and the metallography test under the ASTM A247-16A standard. The spectrometry detects 15 elements in each sample, the carbon equivalent of sample A is 18% and 20% higher in relation to sample B and C, which significantly influences the microstructure. The metallographic tests indicate a pearlitic matrix in each sample, however, there is a different distribution and size of the graphite flakes. According to the SAE J431 standard, each auto part meets the material conditions for the brake disc function.

Two types of scale effects on the nonlinear forced vibration of axially moving nanobeams

Various non-classical continuum mechanics models appearing in previous studies cannot perfectly explain the mechanical properties of micro- and nanomaterials. Establishing a reasonable continuum mechanics model that comprehensively reflects the scale effect on material deformation is of great practical significance for objectively explaining the variation law of mechanical properties of micro- and nanomaterials under the combined action of different scale effects. Based on nonlocal strain gradient theory, a new scale-dependent model is proposed for axially moving nanobeams. In this study, an asymptotic expansion is performed using the multiscale time method to obtain the amplitude-frequency response curve of the equilibrium solutions for the forced vibration problem. Afterwards, the effects of various system parameters, especially the scale parameters, on the resonance curve are examined. Finally, the effects of nonlocal parameters and material characteristic length parameters on the amplitude-frequency response curves are investigated through typical numerical examples. The numerical results show that the nonlocal parameters promote the emergence of the main resonance, whereas the material characteristic length parameters suppress the emergence of the main resonance. Moreover, these parameters also affect the response amplitude and the skewness and jumping point of the amplitude-frequency characteristic curve.

PENERAPAN METODE V-SHAPE LOADING UNTUK MENINGKATKAN PRODUKTIVITAS PC-2000 & PC-1250 DI PIT 10 & 11 MADHANI TALATAH NUSANTARA PT. ARUTMIN INDONESIA TAMBANG ASAMASAM

ABSTRAK Data produktivitas fleets overburden removal PT. Madhani Talatah Nusantara Asamasam Coal Project (ACP) Bulan Januari – Mei 2018 masih jauh di bawah target sehingga analisis untuk mengetahui akar permasalahan dan penyelesaiannya perlu dilakukan. Karakteristik material di ACP merupakan material free dig (no blasting & no ripping), namun semakin dalamnya elevasi banyak terdapat area yang merupakan material keras. Pengambilan data awal dengan metode konvensional loading menunjukkan rendahnya produktivitas disebabkan karena lamanya loading time dan spotting time. Lamanya loading time diakibatkan digging rate yang tinggi, sedangkan lamanya spotting time disebabkan karena jauhnya manuver truk untuk memposisikan siap loading. Untuk mempertahankan efisiensi loading time excavator dan mempercepat waktu manuver truk diperlukan perubahan metode loading, yaitu metode V-shape loading.Metode V-shape loading merupakan metode loading dimana posisi truk membentuk sudut “V” terhadap face penggalian. Penerapan metode V-shape loading memerlukan front kerja dengan luas minimal 20 meter untuk PC-2000 dan 15 meter untuk PC-1250. Metode V-shape loading bertujuan untuk mempercepat waktu manuver truk saat memposisikan siap loading, mengurangi swing radius excavator, dan mengurangi waktu angkat bucket excavator sehingga loading time semakin efisien dan produktivitas akan meningkat. Selain itu, metode ini juga mengurangi waktu delay perbaikan front loading oleh alat dorong dozer karena bekas front loading yang tidak dilalui oleh truk.Metode V-shape loading tidak membutuhkan tambahan biaya untuk diterapkan, hanya diperlukan kepedulian pengawas dalam pengaturan di loading point. Sebelum penerapan metode ini, dilakukan sosialisasi untuk mendapatkan pemahaman dari semua pihak yang terlibat, terutama operator dan pengawas lapangan. Setelah itu, barulah dilakukan implementasi di lapangan dengan pengawasan yang ketat. Hasil penerapan dalam 5 bulan pengamatan menunjukkan adanya efisiensi loading time excavator dan manuver truk sehingga menghasilkan produktivitas yang meningkat. Pada PC-2000, rata-rata produktivitas meningkat 107%, dari sebelumnya 491 bcm/jam menjadi 527 bcm/jam. Sedangkan pada PC-1250, rata-rata produktivitas meningkat 145%, dari sebelumnya 245 bcm/jam menjadi 355 bcm/jam. Kata kunci : produktivitas, V-shape loading ABSTRACT Productivity data fleets overburden removal at PT. Madhani Talatah Nusantara Asamasam Coal Project (ACP) January – May 2019 was below target, so analysis for knowing the root of the problems and this solution is needed. Material characteristic at ACP is free dig material (no blasting & no ripping), but there are much hard material in case of lower elevation. Conventional loading methods showed low productivity was caused by loading time & spotting time above plan. Longer loading time was caused by longer digging rate, while longer spotting time was caused by longer truck positioning ready to load. For maintaining loading time efficiency & maintaining spotting time, V-shape loading method is applied to change conventional loading method.V-shape loading method is loading method which truck position at “V” angle to loading face. Application V-shape loading method needs large front loading minimal 20 meters for PC-2000 and 15 meters for PC-1250. The purpose of V-shape loading method is for speeding up spotting time for ready to load, reducing bucket excavator lifting time so efficiency loading time & productivity increased. Moreover, this method is reducing delay front loading maintenance by dozer because truck spotting did not get through past loading point.V-shape loading method did not need any cost for applying, just needed concern from foreman for observing at loading point. First, all foreman & operator was given socialization for understanding how to apply this method. Then, V-shape loading applied with tight supervision. The result at 5 month application, there was efficiency loading time excavator & spotting time excavator. For PC-2000, average productivity increased 107%, from 492 bcm/hrs to 533 bcm/hrs. Moreover, for PC-1250, average productivity increased 145% from 245 bcm/hrs to 355 bcm/hrs. Keywords : productivity, V-shape loading