Numerical and experimental investigation of the bending zone in free U-bending

With the increasing application of the advanced high strength steel material in the automobile industry, the thickness reduction of the bending area has attracted more and more attention since the product strength is highly influenced by the quality of the bending region. In this paper, three major factors: the thickness reduction, the variation of the local bending radius within the bending zone and the tooling mark on the product's surface are investigated through three different loading patterns for a free U-bending profile numerically and experimentally. The results demonstrate a thinning pattern consists of three peaks over the bending region for large bending ratio (R/t=2.14) and only one peak for small bending ratio (R/t=0.5). Corresponding valleys for the local radius are found to match the thinning pattern. Further, use of finite element simulation can successfully predict the location and the severity of the wear on the product. From the experiment results, even if the metal blank only experienced one stroke, the tooling mark contains both adhesive and abrasive wear. A better understanding of the characteristics of the bending zone is achieved and the findings can help in improving the design process for forming strategies.

Pembesaran Gaya Dalam dan Rasio Kekuatan Elemen Struktur Baja untuk Berbagai Koefisien Modifikasi Respon (R). (Hal. 86-96)

ABSTRAKPerencanaan struktur bangunan yang elastis membuat dimensi struktur yang di desain menjadi lebih besar sehingga biaya pembangunan struktur menjadi meningkat. Struktur bangunan harus di desain dengan suatu konsep tertentu sehingga bangunan tersebut dapat menahan beban yang terjadi secara efisien. Perencanaan struktur bangunan gedung dengan menggunakan koefisien modifikasi respon () ialah merencanakan bangunan untuk mengalami proses plastifikasi pada elemen struktur ketika terjadi gempa. Penelitian ini membandingkan model struktur bangunan dari rangka baja yang terdiri dari 10 lantai, dengan variasi koefisien modifikasi respon () yaitu, =3; 3,5; 4,5; 5; 6; 7; dan 8. Ketujuh model ini juga di dianalisis sesuai dengan sistem penahan gaya seismiknya. Analisis pada penelitian ini menggunakan program ETABS2015. Dari hasil analisis, diperoleh bahwa Semakin kecil nilai koefisien modifikasi respon () yang digunakan mempengaruhi rasio lentur yang terjadi. Perbesaran lentur pada kolom 18 (C18) ketika nilai =3 sebesar 52,47%.Kata kunci: koefisien modifikasi respon (), daktilitas, pembesaran gaya dalam ABSTRACTPlanning an elastic building structure makes the dimensions and designed structures larger and it can increases the cost of the construction itself. The building structures must be designed with a certain concept so, that the building can withstand the loads efficiently. A structure planning using the response modification coefficient () is to plan the building to experience a process of plasticization of the structural elements during an earthquake. This study compares the building structure model of a steel frame consisting of 10 floors, with variation in the modification coefficient of response () from =3; 3,5; 4,5; 5; 6; 7; until 8. The seven models are also analysed according to the seismic force retaining system. The analysis in this study using the ETABS2015 program. From the results of the analysis, it was found that the smaller the value of the response modification coefficient used will affects the bending ratio that occurs. The flexural force when the value of =3 in column 18 (C18) is 52.47%.Keywords: response modification coeffient, ductility, inner force enlargement

Parametric Study on the Interpretation of Wave Velocity Obtained by Seismic Interferometry in Beam‐Like Buildings

In this article, we propose an interpretation of the propagation velocities of the pulse wave obtained in vertical structures through seismic interferometry by deconvolution. The novelty of this article is to propose a parametric study applied to canonical finite‐element models of fixed‐base buildings from pure‐shear to pure‐bending beam‐like buildings, adjusted to equivalent Timoshenko beam‐like structures. For given input seismic motions, the time histories of the horizontal displacement at each floor are obtained and used to estimate the propagation velocity of the pulse wave by deconvolution. A frequency–wavenumber technique is used to highlight the dispersive characteristics of the pulse wave. The obtained velocity is compared with the theoretical dispersion curve of the Timoshenko beam‐like structure and interpreted according to the nature of the structure. We propose a corrective coefficient to link the first resonance frequency of the building to the velocity obtained by deconvolution, according to the shear‐to‐bending ratio. Finally, we compare specific Timoshenko beam models with a number of previously published studies on the experimental interpretation of velocity in real‐case buildings for which soil–structure interaction conditions are different from the fixed‐base conditions of the Timoshenko beam‐like structure.

X-ray Microscopic Study on Disintegration of Granite Residual Soil

In order to study the evolution of cracks in the initial disintegration process of granite residual soil, this study used CT scanner to scan the sample before and after 60s disintegration. Internal cracks are statistically analyzed by 3D reconstruction techniques. The initial crack content of granite residual soil is 0.8%, and it increases to 8.1% after 60s disintegration. Internal cracks of the sample are transformed into complex connected cracks, and there are many large pores formed by erosion and presented as complex geometry shape. The geometry of cracks is analyzed from three aspects: width, length and bending ratio. It is found that cracks have strong linear characteristics after 60s disintegration, which may be related to the initial rapid infiltration damage.

On the mechanisms of modal damping in FRP/honeycomb sandwich panels

Sandwich panels made of fibre-reinforced plastic (FRP) skins and a honeycomb core can be effectively damped through the choice of the skin and especially of the core materials. Because the core is often highly damped, a lateral deflection that causes more shearing of the core than bending of the skin increases sandwich damping. Aside from the skin and the core material properties, the shearing/bending ratio depends on a number of other, often interacting, factors, including the sandwich planar as well as transverse dimensions, the particular modal pattern in which the panel vibrates and its relationship to the type of skin layup, as well as the panel end conditions. In the present work, using a simple, first-order shear deformation theory, damping results have been produced for simple modes of vibration of a sandwich panel comprising composite skins and a damped honeycomb core, demonstrating the mechanisms by which the above factors affect the FRP skin/honeycomb core sandwich damping.

Experimental and Numerical Investigations of Push Bending of Copper Thin Walled Tubes

In order to realize the successful process of forming the thin walled tubes in different industries, numerous methods have been registered by researchers. The tube push bending technique is a new process which allows forming tubes with lower bending ratio. In this study, the effects of push bending process on thickness variation and stress distribution are investigated. In addition, experimental and analytical studies have been dealt with in order to evaluate different bending radii. Results show close congruity between experiment and simulation.

Prediction of Minimum Bending Ratio of Aluminum Sheets From Tensile Material Properties

One of the most widely involved operations in sheet metal forming processes in aircraft industry is bending, particularly, air bending as a simple process. For this reason, the bendability of aluminum alloys is an important material property, which determines the minimum radius to which a sheet may be bent without cracking. Hence, the challenging issue, on which this paper focuses, is to predict this material parameter from other material parameters commonly measured during standard tensile tests. For this prediction, a finite element model and a response surface model are elaborated and, as a result, a relatively simple formula is proposed to calculate the minimum bending radius from the reduction in the area at fracture, the strain hardening exponent, and the yield stress, which are material parameters available from tensile tests.