scholarly journals EXPERIMENTAL STUDY ON POST-BUCKLED COMPOSITE SINGLE-STRINGER SPECIMENS WITH INITIAL DELAMINATION UNDER FATIGUE LOADS

2021 ◽  
Author(s):  
ANTONIO RAIMONDO ◽  
JAVIER PAZ MENDEZ ◽  
CHIARA BISAGNI
Keyword(s):  
Static Load ◽  
Compressive Load ◽  
Fatigue Tests ◽  
Load Level ◽  
Image Correlation ◽  
Compressive Behavior ◽  
Fatigue Load ◽  
Out Of Plane ◽  
Post Buckling ◽  
Correlation System

The fatigue damage tolerance of a composite stiffened structure in post-buckling conditions is experimentally investigated in this work. Single-stringer specimens with an initial delamination, artificially created during the manufacturing process, are tested under cyclic compressive load. Six nominally identical specimens are manufactured: two tested under quasi-static load to understand the compressive behavior of the structure and four under fatigue load cycling between pre- and post-buckling conditions at two different maximum loads. During the tests, digital image correlation system and ultrasonic C-scan are adopted to follow the evolution of the out-of-plane displacements and the propagation of the delamination. Depending on the load level, the delamination starts to grow already in the first cycle or after a few thousand cycles, but in both cases the propagation is fast at the beginning, then slows down gradually. The fatigue tests are interrupted after 150,000 cycles and the specimens are subjected to quasi-static compressive load to evaluate the residual strength of the structure.

scholarly journals Experimental investigation of the failure modes of in-plane loaded inserts in CFRP sandwich panels

2018 ◽  
Vol 188 ◽  
pp. 04025
Author(s):  
Philip Richert ◽  
Athanasios Dafnis ◽  
Kai-Uwe Schröder
Keyword(s):  
Experimental Investigation ◽  
Digital Image Correlation ◽  
Digital Image ◽  
Failure Modes ◽  
Image Correlation ◽  
Honeycomb Core ◽  
Out Of Plane ◽  
Aluminum Honeycomb ◽  
Correlation System ◽  
Sandwich Materials

The aim of this paper is the experimental determination and investigation of the different failure modes of various insert types under inplane load in sandwich materials with CFRP face sheets and a perforated aluminum honeycomb core. In addition, also insert under an out-of-plane load are tested. In total three different kind of inserts are investigated: blind inserts, trough-the-thickness inserts and special inserts which are developed within the iBOSS research project. The inserts are tested until failure and monitored with the digital image correlation system Aramis. This test monitoring is intended to determine the first failure mode. It is shown that this works well for out-of-plane loaded insert connections and the special inserts under in-plane load. However, this does not work so well with in-plane loaded standard inserts. In further investigations, a failure of the adhesive shortly before failure of the top layers can be shown.

scholarly journals Influence of the Fatigue Load Level and the Hole Diameter on the Laminate Structure’s Fatigue Performance

2018 ◽  
Vol 2018 (10) ◽  
pp. 21-30
Author(s):  
Małgorzata Zalewska
Keyword(s):  
Fatigue Testing ◽  
Damage Tolerance ◽  
Fatigue Tests ◽  
Load Level ◽  
Hole Diameter ◽  
Test Results ◽  
Fatigue Load ◽  
Loading Mode ◽  
Load Limit ◽  
Two Parameters

Abstract Damage tolerance of composite aircraft structure is one of the main areas of research, important when a new product is being developed. There are a number of variables, such as damage characteristics (dent depth, delamination area) and loading parameters (load type, amplitude of cyclic loading, load sequence) that need to be investigated experimentally [1]. These tests of composite materials are usually performed at an element level and are carried out in order to validate the analytical model, developed to predict the full-scale component’s behaviour. The paper presents the results of compression testing of the [36/55/9] carbon fibre/epoxy laminate, manufactured with the Automated Fibre Placement technology (AFP) and subjected to static and fatigue loads. The laminate compression loading mode was achieved through sandwich 4-point flexure. At the stage of fatigue testing, two parameters were investigated: the damage size, simulated by the hole diameter and the fatigue load level. Based on the test results, the laminate fatigue load limit equal to 75% of the OHC failure load was evaluated. By collating the static and fatigue tests results, the damage tolerance characteristic of the considered laminate was created.

scholarly journals A novel concept of modular shape-adaptable sandwich panel with distributed actuation based on shape memory alloys

2021 ◽  
pp. 1045389X2110572
Author(s):  
Oleg Testoni ◽  
Sandro Christen ◽  
Sampada Bodkhe ◽  
Andrea Bergamini ◽  
Paolo Ermanni
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Sandwich Panel ◽  
Element Model ◽  
Image Correlation ◽  
Compliant Joints ◽  
Actuation System ◽  
Out Of Plane ◽  
Correlation System ◽  
Novel Concept

This work introduces a novel concept of modular, shape-adaptable sandwich panel with a distributed actuation system based on shape memory alloys (SMA). The panel consists of a modular arrangement of rigid cells connected with compliant active joints. Each joint hosts a SMA wire, which can be controlled independently, enabling the panel to achieve multiple shapes and complex curvatures with a single design. A numerical model of the actuators is developed combining the SMA model proposed by Brinson with a finite element model of the compliant joints, and validated against experimental results. Further, a demonstrator of the panel is manufactured and tested implementing four different actuation patterns and measuring the final shapes with a digital image correlation system. The results prove the capability of the proposed concept to achieve both in plane and out-of-plane deformations in the order of millimeters to centimeters, and to reproduce shapes with double curvatures. With the possibility to integrate sensors and additional components inside the core, the proposed shape-adaptable panel can be used to realize smart structures, which might be used for morphing aerodynamic surfaces or reconfigurable space structures.

scholarly journals Sensor Integrated Load-Bearing Structures: Measuring Axis Extension with DIC-Based Transducers

Sensors ◽  
2021 ◽  
Vol 21 (12) ◽  
pp. 4104
Author(s):  
Nassr Al-Baradoni ◽  
Peter Groche
Keyword(s):  
Cost Effective ◽  
Image Correlation ◽  
Maximum Deviation ◽  
Single Image ◽  
Eccentric Load ◽  
Load Bearing ◽  
Out Of Plane ◽  
Axis Extension ◽  
Plane Displacement ◽  
Imaging Sensor

In this paper we present a novel, cost-effective camera-based multi-axis force/torque sensor concept for integration into metallic load-bearing structures. A two-part pattern consisting of a directly incident and mirrored light beam is projected onto the imaging sensor surface. This allows the capturing of 3D displacements, occurring due to structure deformation under load in a single image. The displacement of defined features in size and position can be accurately analyzed and determined through digital image correlation (DIC). Validation on a prototype shows good accuracy of the measurement and a unique identification of all in- and out-of-plane displacement components under multiaxial load. Measurements show a maximum deviation related to the maximum measured values between 2.5% and 4.8% for uniaxial loads ( and between 2.5% and 10.43% for combined bending, torsion and axial load. In the course of the investigations, the measurement inaccuracy was partly attributed to the joint used between the sensor parts and the structure as well as to eccentric load.

scholarly journals Characterization and ballistic performance of thin pre-damaged resin-starved aramid-fiber composite panels

2021 ◽  
pp. 004051752110134
Author(s):  
Cerise A Edwards ◽  
Stephen L Ogin ◽  
David A Jesson ◽  
Matthew Oldfield ◽  
Rebecca L Livesey ◽  
...  
Keyword(s):  
Fiber Composite ◽  
Plane Deformation ◽  
Ballistic Impact ◽  
Image Correlation ◽  
Composite Panel ◽  
Composite Panels ◽  
Micro Computed Tomography ◽  
Ballistic Performance ◽  
Low Level ◽  
Out Of Plane

Military personnel use protective armor systems that are frequently exposed to low-level damage, such as non-ballistic impact, wear-and-tear from everyday use, and damage during storage of equipment. The extent to which such low-level pre-damage could affect the performance of an armor system is unknown. In this work, low-level pre-damage has been introduced into a Kevlar/phenolic resin-starved composite panel using tensile loading. The tensile stress–strain behavior of this eight-layer material has been investigated and has been found to have two distinct regions; these have been understood in terms of the microstructure and damage within the composite panels investigated using micro-computed tomography and digital image correlation. Ballistic testing carried out on pristine (control) and pre-damaged panels did not indicate any difference in the V50 ballistic performance. However, an indication of a difference in response to ballistic impact was observed; the area of maximal local out-of-plane deformation for the pre-damaged panels was found to be twice that of the control panels, and the global out-of-plane deformation across the panel was also larger.

scholarly journals In-Process Measurement of Three-Dimensional Deformations Based on Speckle Photography

2021 ◽  
Vol 11 (11) ◽  
pp. 4981
Author(s):  
Andreas Tausendfreund ◽  
Dirk Stöbener ◽  
Andreas Fischer
Keyword(s):  
Evaluation Method ◽  
Process Analysis ◽  
Plane Deformation ◽  
Three Dimensional ◽  
Machining Process ◽  
Image Correlation ◽  
Speckle Photography ◽  
Process Measurement ◽  
Out Of Plane ◽  
Plane Deformations

In the concept of the process signature, the relationship between a material load and the modification remaining in the workpiece is used to better understand and optimize manufacturing processes. The basic prerequisite for this is to be able to measure the loads occurring during the machining process in the form of mechanical deformations. Speckle photography is suitable for this in-process measurement task and is already used in a variety of ways for in-plane deformation measurements. The shortcoming of this fast and robust measurement technique based on image correlation techniques is that out-of-plane deformations in the direction of the measurement system cannot be detected and increases the measurement error of in-plane deformations. In this paper, we investigate a method that infers local out-of-plane motions of the workpiece surface from the decorrelation of speckle patterns and is thus able to reconstruct three-dimensional deformation fields. The implementation of the evaluation method enables a fast reconstruction of 3D deformation fields, so that the in-process capability remains given. First measurements in a deep rolling process show that dynamic deformations underneath the die can be captured and demonstrate the suitability of the speckle method for manufacturing process analysis.

The Effect of Stitching on Compression Behavior of Stiffened Composite Panels

2001 ◽  
Author(s):  
Sung S. Suh ◽  
H. Thomas Hahn ◽  
Nanlin Han ◽  
Jenn-Ming Yang
Keyword(s):  
Beneficial Effect ◽  
Compression Behavior ◽  
Stiffened Panels ◽  
Shell Elements ◽  
Stitch Density ◽  
Stiffened Composite Panels ◽  
Out Of Plane ◽  
Post Buckling ◽  
Post Impact ◽  
Good Agreement

Abstract Failure of stiffened panels under compression is preceded by buckling of their skin and hence is affected by the presence of out-of-plane stresses. One of the promising methods of preventing premature delamination is stitching. The present paper discusses the effect of such stitching on compression behavior of blade-stiffened panels that were fabricated from plain weave AS4/3501-6 through resin film infusion process. Kevlar 29 yarn was used at a stitch density of 9.92 stitches per cm2. Some of the panels were damaged by drop-weight impact before compression testing. For comparison purposes unstitched panels with the same materials and dimensions were also tested under the same loading conditions. Stitching resulted in a 10% improvement in strength in the absence of any intentional damage. The beneficial effect of stitching was most obvious when the panels were impacted on a flange: a 50% improvement was observed in post-impact strength. However, stitching could not prevent stiffener from failure when impacted directly. Thus stitching had no beneficial effect when impact occurred on a stiffener. A buckling and post-buckling analysis was carried out using 3-D shell elements on the Abaqus. Predictions were in fairly good agreement with the experimental data.

Using the Simplified 3D DIC Method to Measure the Deformation of 3D Surface

2011 ◽  
Vol 121-126 ◽  
pp. 3945-3949 ◽  
Author(s):  
Shih Heng Tung ◽  
Jui Chao Kuo ◽  
Ming Hsiang Shih ◽  
Wen Pei Sung
Keyword(s):  
Measurement Accuracy ◽  
Good Accuracy ◽  
Correlation Method ◽  
Image Correlation ◽  
2D Digital Image Correlation ◽  
Plate Specimen ◽  
Before And After ◽  
Out Of Plane ◽  
Plane Displacement ◽  
2D And 3D

In recent years, 2D digital image correlation method (DIC) has been widely used in the measurement of plane strain. However, out-of-plane displacement could be induced during the loading and it would affect the measurement accuracy. Thus, a 3D measurement is necessary. This study utilizes a simplified 3D DIC to measure the geometry of an object before and after deformation. Then the finite element concept is involved to determine the strain after deformation. A flat plate specimen with in-plane and out-of-plane displacement is observed. Both 2D and 3D DIC are used to analyze the strain. The results show that using 3D DIC to measure strain is feasible and with a very good accuracy.

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