Linear-nonlinear stiffness responses of carbon fiber-reinforced polymer composite materials and structures: a numerical study

The stiffness response or load-deformation/displacement behavior is the most important mechanical behavior that frequently being utilized for validation of the mathematical-physical models representing the mechanical behavior of solid objects in numerical method, compared to actual experimental data. This numerical study aims to investigate the linear-nonlinear stiffness behavior of carbon fiber-reinforced polymer (CFRP) composites at material and structural levels, and its dependency to the sets of individual/group elastic and damage model parameters. In this regard, a validated constitutive damage model, elastic-damage properties as reference data, and simulation process, that account for elastic, yielding, and damage evolution, are considered in the finite element model development process. The linear-nonlinear stiffness responses of four cases are examined, including a unidirectional CFRP composite laminate (material level) under tensile load, and also three multidirectional composite structures under flexural loads. The result indicated a direct dependency of the stiffness response at the material level to the elastic properties. However, the stiffness behavior of the composite structures depends both on the structural configuration, geometry, lay-ups as well as the mechanical properties of the CFRP composite. The value of maximum reaction force and displacement of the composite structures, as well as the nonlinear response of the structures are highly dependent not only to the mechanical properties, but also to the geometry and the configuration of the structures

Kajian Park and Ride Untuk Busway Jakarta

As one of the TDM alternative for improving bus public transport services, park-and-ride (P&R) could support a larger mode shift from private car users. Experience from other developed countries proves that P&R could bring more passenger uses mass transit system. Two important parameter for the successful of P&R services are location and tarif. In Jakarta, the successful implementation of Blok M-Kota first busway corridor could not be followed by others, due to low quality of transfer facilities. This paper reviews the theoretical ideal P&R and practical measures to be discussed for the Jakarta busway corridors

Interlaminar damage behavior of CFRP composite laminates under cyclic shear loading conditions

This paper provides quantitative description of interlaminar damage process in CFRP composite laminates under cyclic shear loading. Quasi-static end-notched flexural (ENF) test on 16-ply CFRP composite laminate beam, [0]16 and its complementary validated FE model provide the reference “no-interlaminar damage” condition. Two identical ENF samples were fatigue to 50000 cycles, but at different load amplitude of 90 and 180 N, respectively (Load ratio, R = 0.1) to induce selectively property degradation at the interface crack front region. Subsequent quasi-static ENF tests establish the characteristic of the interlaminar damage degradation. The residual peak load for the fatigued ENF samples is measured at 1048 and 914 N for the load amplitude of 90 and 180 N, respectively. Cyclic interlaminar shear damage is represented by a linear degradation of the residual critical energy release rate, GIIC with the accumulated damage. Reasonably close comparisons of the predicted residual load-displacement responses with measured curves serve to verify the suitability of the assumed bilinear traction-separation law for the cyclic cohesive zone model (CCZM) use

Adjustment of Daily Activities: the Influence of Smartphone Adoption on the Travel Pattern of Mobile Professionals in the Greater Jakarta Area

The swift augmentation in the adoption of smartphones, the gadget that resulted from the convergence of Information and Communication Technology (ICT), potentially transforms people\u27s life in myriad dimensions. One potential change induced by smartphones, is how people restructure their daily agenda and consecutively influence their travel pattern. To understand it, this study theoretically reviews mobile professional work, smartphone adoption, and how people conduct their mobile interaction, planning and execution of daily activities. Mobile professionals, the cohort of professionals that spend more than 20% of their total working time moving around out of their work environment; they are important beneficiaries of smartphones and have been chosen as the target of this study. Empirical results of mobile professionals´ experiences in the Greater Jakarta Area are presented at this juncture. Furthermore, their adjustment of activities as a dynamic response to receiving extensive information via smartphones is also analysed. The results indicate that there is a strong adjustment of daily activities by mobile professionals. Through those changes, the transformation of daily travel patterns related to the activity is also brought about by the use of this high-end ICT contrivance

Strain rate-dependent deformation and failure process of adhesive joints

Rate-dependent deformation and failure process of adhesive joints are investigated in this study. For this purpose, acrylic foam pressure sensitive adhesive (PSA) was employed with aluminum adherents. Tensile and shear loading of the adhesive joint was applied at displacement rates ranging from 5 to 500 mm/min. Results show that the failure process under tensile loadings start with initiation of cavities, hardening through fibrillation process and final fracture of the fibrils. For shear loading the failure process is a combination of fibrillation processes, shear flow, and by interfacial sliding. Both modulus and strain energy density at fracture reach maximum value at a displacement rate of 100 mm/min under tension, while continuously increase with displacement rate under shear loading. Adhesive failure dominates at low loading rate (below 10 mm/min.), while mixed-mode and cohesive failure are common at faster loading rates above 250 mm/min. Finite element employing Yeoh constitutive model adequately predicts viscous shear deformation of the PSA joints

Deformation mechanics of sputtered copper layers during nanoindentation tests

The mechanical properties of the thin sputtered copper layer on the SiO2-coated silicon substrate is needed as part of the requirements in quantifying the reliability of the Through-Silicon Via (TSV) interconnects. In this respect, two different Cu coating layers, each from the different sputtering process, are examined. A series of nanoindentation tests are performed on the Cu coating layer samples with indenter speeds ranging from 80 to 400 nm/s, and the indentation depths of 320 nm. The properties of elastic modulus, hardness and the hardening behavior of the Cu coating layers have been quantified. Results show that the coating with higher contamination of C at 8.41 wt. % displays a significant hardening and a peak load level, as reflected in the measured nanoindentation load-displacement curves. However, insignificant effect of the applied probe displacement speeds up to 400 nm/s on the resulting properties of the coating is registered. The Johnson-Cook constitutive equation adequately describes the strain rate-dependent hardening behavior of the Cu coating layer

Cohesive zone modelling of mode III delamination using the edge crack torsion test

In the experimental studies of mode III delamination using the edge crack torsion test, the crack initiation and propagation measurement are always difficult. This information could be obtained through numerical modelling. The objective of this study is to propose a guideline to model mode III delamination behaviour using cohesive elements. Finite element models of an edge crack torsion specimen were developed based on the data from the literature. The delamination behaviour of the specimen along the pre-crack, which was located at the mid-Thickness location, was modelled using cohesive elements. Through parametric studies, it was found that for reliable numerical modelling, a mesh size of 0.5 mm was suggested, which provided three elements in the cohesive zone. As for the interface strength, it was recommended to choose 80 MPa. In addition, a viscosity parameter of 110-3 was found to be a good choice for reasonable computational time and converged numerical results. Besides, the interface stiffness was suggested to be 4106 MPa/mm. Furthermore, the fracture process zone contour revealed that the delamination was started at a normalised location of approximately 0.7. Not only that, the fracture energy and strain distribution plots have shown the delamination was mode III dominated within the normalised distance of 0.34-0.86. The results from this study suggested that cohesive zone modelling is a useful method for the detailed analysis of the mode III delamination of an ECT specimen. The numerical modelling approach suggested from this study could be applied to ECT specimens at various different initial crack lengths. It also has the potential to be used to simulate the mode III delamination of other various types of laminated composites