Hozhabr Mozafari

In plane compressive response and crushing of foam filled aluminum honeycombs

In this paper, the influence of foam filling of aluminum honeycomb core on its in-plane crushing properties is investigated. An aluminum honeycomb core and a polyurethane foam with densities of 65, 90, and 145 kg/m3 were used to produce foam filled honeycomb panels, and then experimental quasi-static compression tests were performed. Moreover, finite element model, based on the conducted tests, was developed. In the finite element analyses, three different polyurethane foams were used to fill three different honeycomb cores. The effects of foam filling of aluminum honeycomb core on its in-plane mechanical properties (such as mean crushing strength, absorbed energy, and specific absorbed energy) were analyzed experimentally and numerically. The results showed that the foam filling of honeycomb core can increase the in plane crushing strength up to 208 times, and its specific absorbed energy up to 20 times. However, it was found that the effect of foam filling decreases in heavier honeycombs, producing an increment of the above mentioned properties only up to 36 and 6 times, respectively.

Computed tomography-based reconstruction and finite element modelling of honeycomb sandwiches under low-velocity impacts

The honeycomb sandwiches are widely used in the transportation engineering for the realization of lightweight and crashworthy structures. However their application requires a better understanding of their impact response. Aims of this paper are the numerical investigation of aluminium honeycomb sandwiches subjected to low-velocity impact tests and the validation of finite element (FE) results. Before and after the low-velocity impact tests at different velocities, three dimensional (3D) reconstructions of the honeycomb panels have been carried out by a computed tomographic system in order to acquire exactly the dimension and the shape of the damage and to obtain information about geometry and cells defects. The FE models have been computed from CT data of the undamaged panels. The direct comparison has been done by superimposing the deformed images obtained from FE analyses and from 3D CT space reconstructions. The numerical model was also validated comparing the FE results with experimental data.

Finite element analysis of foam-filled honeycomb structures under impact loading and crashworthiness design

ABSTRACT The aim of this research is the investigation of foam-filled honeycomb sandwich panels under in-plane impact loading and the analysis of their crashworthiness. This paper presents a finite element analysis of foam-filled honeycomb sandwiches under in-plane impact loading. Three different aluminium honeycombs filled with three different polyurethane foams were considered in the numerical simulation, and results were compared with those obtained for bare honeycomb panels. For what concerns the crashworthiness analysis, the response of the foam-filled honeycomb panels under out-of-plane impacts was compared with those of unfilled honeycomb panels and circular tubes.

Numerical and experimental investigation of corrugated tubes under lateral compression

ABSTRACT As a common type of energy absorbers, thin-walled structures have been extensively used in crashworthiness application in many industries. The goal of this research is the optimisation of the crushing parameters of corrugated tubes in terms of the number and shape of corrugations. Six different configurations were experimentally investigated; one refers to the straight tube without configurations and the others to corrugated tubes with different geometrical parameters. First, lateral compression tests were carried out and the experimental results were used to validate the finite element models. Other six different configurations of corrugated tubes were analysed by means of finite element simulations. The obtained results demonstrate the advantage of the corrugated tubes with respect to the straight tube in terms of the total absorbed energy and the crushing load. Moreover, the geometrical shape of corrugation (i.e. the ratio of corrugation base to its depth) plays an important role in enhancing the efficiency of the corrugated tubes.

Vibration analysis of foam filled honeycomb sandwich panel – numerical study

Abstract Honeycomb structures are widely used in transportation industries. Owing to their lightweight, high strength, damage tolerance and thermal resistance, they are extensively used as a solution to modern engineering problems in the vehicle structure’s design. Furthermore, lightweight polymeric foams can be exploited to improve mechanical properties of sandwich panels. Recently, foam filled honeycomb sandwich panels have been proposed in order to benefit from mechanical characteristics of both honeycomb cellular structure and polymeric foam in the core of the sandwich panel. Until now, most of the investigations were delved into the mechanical properties of the foam filled honeycomb sandwich panels; in plane crushing, out of plane impact and local indentation response of these panels were broadly discussed previously. On the other hand, since many vehicles’ failure are related to severe vibrations, clear understanding of foam filled honeycomb panels eigenvibration properties is vital. In this paper, vibration frequencies and mode shape of honeycomb sandwich panels with different cores are studied using numerical method. At the first step, elastic mechanical properties of polyurethane foams were determined by experimental tests, next a finite element model was developed by means of Abaqus software package. Parameters, such as first resonant frequency, mode shapes and influence of foams on local vibration of the honeycomb core were investigated.

Fracture mechanics of planetary gear set by using extended finite element method-linear elastic fracture mechanics approach

Abstract Contour integral method is the conventional approach in order to characterise main crack parameters in fracture studies. This method is used in verity fields in fractures mechanics because of its capability in linear and non-linear fracture mechanics. Whereas, requirements such as mesh singularity in crack tip and refined layers of elements in surrounding contours, which increase computing time and make it prolix for large components. The main aim of this paper is to develop an extended finite element method-linear elastic fracture mechanics (XFEM-LEFM) model to impart XFEM advantages in survey of fracture mechanics of planetary gear sets. At first main crack parameters of root crack of the planet gear have been obtained and compared with conventional method, and after that crack growth path is predicted, and finally effect of rim thickness is investigated and compared with other researches to illustrate the efficiency of the developed model. For this purpose, Python script code is generated to automatically calculate the stress intensity factors of root crack and after that simulate the crack growth path until final fracture.

Crashworthiness Analysis of a Novel Aluminum Bi-tubular Corrugated Tube—Experimental Study

Crashworthiness is the ability of a structure to protect its occupant during an impact. Metallic tubes are deemed as one of the most popular structures to dissipate crushing energy during collision. Easy manufacturing, low cost of assembly, and high energy absorption capacity can be counted as the main merits of these structures. Introducing corrugations along the length of circular tubes is a well-known method to improve crashworthiness. It was found that the uniformity of the load–displacement behavior of crushed corrugated tubes improved, compared with that one for tubes without corrugation. In this paper, a novel bi-tubular corrugated tube is designed, and experimental compression tests were conducted to evaluate the crashworthiness characteristics under lateral loading conditions. Critical crashworthiness parameters such as the total absorbed energy were extracted, and the efficacy of the structure was compared with its conventional corrugated counterpart. It was found that the novel corrugated tube can interestingly improve the crashworthiness of the energy absorber device. Moreover, it was observed that the bi-tubular tube’s efficacy improves by adding more corrugations along the tube. To wrap it up, a novel bi-tubular tube with continuous corrugation along the tube can strengthen the crashworthiness of the conventional corrugated tubes by large.

Numerical and Experimental Investigation on Corrugation Geometry for Metallic Tubes under Lateral Loading

Energy absorption devices are being used to protect structures from severe damages and reduce injury to occupants during accidents. The integrated characteristics of crash absorption devices can be classified as high energy absorption capacity, light-weight, and cost-effective. One of the thin-walled structures which has drawn the attention of scientists is corrugated tube structure. In this paper, the effect of corrugation geometry on the crushing parameters of an aluminum corrugated tube is investigated. In this regard, different elliptical corrugation shapes were deemed and the compression response was numerically evaluated under lateral quasi-static loading. Finally, the crashworthiness parameters were extracted and compared to determine the influence of corrugation shape on the crashworthy response. Our results showed that using vertical elliptical corrugation decrease the densification point. Moreover, there is a gradual enhancement of mean crushing load by moving from the horizontal elliptical corrugations to the vertical ones. Also, by modifying of corrugation shape, the stress variation pattern changes, significantly.

Migration resistance of esophageal stents: The role of stent design

OBJECTIVE Stenting is one of the major treatments for malignant esophageal cancer. However, stent migration compromises clinical outcomes. A flared end design of the stent diminishes its migration. The goal of this work is to quantitatively characterize stent migration to develop new strategies for better clinical outcomes. METHODS An esophageal stent with flared ends and a straight counterpart were virtually deployed in an esophagus with asymmetric stricture using the finite element method. The resulted esophagus shape, wall stress, and migration resistance force of the stent were quantified and compared. RESULTS The lumen gain for both the flared stent and the straight one exhibited no significant difference. The flared stent induced a significantly larger contact force and thus a larger stress onto the esophagus wall. In addition, more migration resistance force was required to pull the flared stent through the esophagus. This force was inversely related to the occurrence rate of stent migration. A doubled strut diameter also increased the migration resistance force by approximately 56%. An increased friction coefficient from 0.1 to 0.3 also boosted the migration resistance force by approximately 39%. SUMMARY The mechanical advantage of the flared stent was unveiled by the significantly increased contact force, which provided the anchoring effect to resist stent migration. Both the strut diameter and friction coefficient positively correlated with the migration resistance force, and thus the occurrence of stent migration.