Nonlinear Flexural Modeling for Epoxy Resin Materials

2011 ◽  
Author(s):  
Masoud Yekani Fard ◽  
Yingtao Liu ◽  
Aditi Chattopadhyay
Keyword(s):  
Composite Structures ◽  
Strain Softening ◽  
Constitutive Models ◽  
Polymeric Materials ◽  
Local Stress ◽  
Image Correlation ◽  
Flexural Behavior ◽  
Peak Strain ◽  
Stress Strain ◽  
Tension And Compression

Polymer composite structures are usually subjected to large flexural loadings, so the flexural behavior of these structures and their constituents are critical to their use. A novel approach for polymeric materials with strain softening model in tension and compression is developed to investigate the flexural behavior of Epon E 863. The tension and compression model consists of a bilinear ascending curve in pre-peak, strain softening followed by constant plastic flow in the post-peak response. The effects of softening localization on flexural response are considered. Local stress strain tension and compression responses, using digital image correlation system, are used for material characterization. Closed form expressions for flexural behavior are developed. The structural response of beams under three and four point bending and round plate on three symmetrical supports are studied experimentally and analytically. Results show that direct use of uniaxial tension and compression stress strain models underestimates the flexural load carrying capacity. Flexural over-strength factor obtained from inverse analysis of beam under three point bending is conservative and it could be used to modify the constitutive models for analyzing a structural system.

Environmental Effects on Flexural Over-Strength Factor of Epoxy Resin Materials

2013 ◽  
Author(s):  
Masoud Yekani Fard ◽  
Aditi Chattopadhyay ◽  
Brian Raji
Keyword(s):  
Epoxy Resin ◽  
Environmental Effects ◽  
Composite Structures ◽  
Stress Gradient ◽  
Polymeric Materials ◽  
Image Correlation ◽  
Flexural Behavior ◽  
Strength Factor ◽  
Loading System ◽  
Tension And Compression

Polymer composite structures are usually subjected to large flexural loadings during their life-span of the structures, so the flexural behavior of these structures and their constituents in different environmental conditions are critical to their use. A novel analytical approach for epoxy resin semi-brittle materials with strain softening model in tension and compression has been developed to investigate the flexural behavior of these materials. The value of the flexural over-strength factor which is the ratio of the flexural strength to the strength obtained from tension and compression stress strain models depends on stress gradient, size and loading system and it has already been evaluated at the laboratory condition. The mechanical properties of epoxy resin materials are sensitive to environmental effects at which they are loaded. The influence of temperature 60°C and humidity 90% Rh on tension, compression and flexural behavior of epoxy resin polymeric materials PRI and PR 520 have been investigated. Digital image correlation system was used for material characterization. The effects of heat and humidity on softening localization in flexural response were considered. The influence of heat and humidity on the flexural over-strength factor was evaluated.

scholarly journals An examination of initial structural degradation in tubular braided composites through region-by-region strain analysis

2020 ◽  
Vol 15 ◽  
pp. 155892502097832
Author(s):  
Eric A Lepp ◽  
Jason P Carey
Keyword(s):  
Polynomial Regression ◽  
Strain Analysis ◽  
Local Stress ◽  
Image Correlation ◽  
Tensile Failure ◽  
Braided Composites ◽  
Growth Trend ◽  
Stress Strain ◽  
Structural Degradation ◽  
Strain Data

The objective of this study was to characterize the early structural degradation behavior of tubular braided composites (TBCs) under quasi-static tension through direct quantification of the surface strains developed in their yarn-reinforced and unreinforced (resin-rich) material regions. Kevlar-epoxy TBCs with varying braid angles and numbers of yarns were analyzed through quasi-static testing and stereo digital image correlation (DIC) analysis to understand how the yarn-reinforced and resin-rich regions deformed under tensile loads up to the initiation of structural degradation within the braid structure. Structural weakening was confirmed to initiate in the unreinforced, resin-rich regions of the TBC specimens by way of a normal tensile failure mode, as the strains developed within these regions were the first to deviate from a linear-elastic growth trend and also exceed the expected strain to failure of their constituent material. Through two-way full-factorial ANOVA analysis with a 95% confidence interval, the stress required to initiate degradation within these regions was found to depend significantly upon both the quantity and angular orientation of the preform yarns, the former to a markedly lower extent. The maximum strain accumulated in the resin-rich regions upon their degradation was found to not statistically depend on either of these parameters, affirming that it is purely defined by the strength properties of the constituent neat resin material. To provide conservative and repeatable estimates of the stress to failure in TBC structures, it is recommended that this quantity be estimated from both the global stress-strain data of the entire specimen and the local stress-strain data measured exclusively within its resin-rich regions, with the lower of the two taken. Through these means, the relationship between a TBC’s preform geometry and its stress to failure may be optimally modeled using a polynomial regression trend.

The Stress-Strain Behavior of Densified Mix Design of Concrete

2002 ◽  
Vol 18 (4) ◽  
pp. 185-192
Author(s):  
Ping-Kun Chang
Keyword(s):  
High Performance ◽  
Strain Softening ◽  
High Performance Concrete ◽  
Strain Curve ◽  
Type I ◽  
Peak Strain ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Strain Behavior ◽  
Slump Flow

ABSTRACTThis paper investigates the compressive strength and workability of High-Performance Concrete (HPC) which yields a slump at 250 ± 20mm and a slump flow at 650 ± 50mm. From the complete stress-strain curve, it shows the peak strain will be higher while the strength increases. Two kinds of the post failure models can be distinguished. The first type (Type I) is called strain softening and the second type (Type II) is called strain snapping back. Also, it is found that the modulus of elasticityEcdecreases as the volume of cementitious pasteVpincreases. On the other hand, Poisson's ratio ν increases asVpincreases.

scholarly journals Virtual Extensometer Analysis of Martensite Band Nucleation, Growth, and Strain Softening in Pseudoelastic NiTi Subjected to Different Load Cases

Materials ◽  
2018 ◽  
Vol 11 (8) ◽  
pp. 1458
Author(s):  
Cagatay Elibol ◽  
Martin Wagner
Keyword(s):  
Strain Softening ◽  
Nucleation Site ◽  
Shear Loading ◽  
Gauge Length ◽  
Surface Strain ◽  
Image Correlation ◽  
Localized Deformation ◽  
Stress Strain ◽  
Softening Behavior ◽  
Characteristic Features

Pseudoelastic NiTi shape memory alloys exhibit different stress–strain curves and modes of deformation in tension vs. compression. We have recently shown that under a combination of compression and shear, heterogeneous deformation can occur. In the present study, we use digital image correlation to systematically analyze how characteristic features of the nominally uniaxial engineering stress–strain curves (particularly the martensite nucleation peak and the plateau length) are affected by extensometer parameters in tension, compression, and the novel load case of shear-compression. By post-experimental analysis of full surface strain field data, the effect of the placement of various virtual extensometers at different locations (with respect to the nucleation site of martensite bands or inhomogeneously deforming regions) and with different gauge lengths is documented. By positioning an extensometer directly on the region corresponding to the nucleating martensite band, we, for the first time, directly record the strain-softening nature of the material—a specific softening behavior that is, for instance, important for the modeling community. Our results show that the stress–strain curves, which are often used as a basis for constitutive modeling, are affected considerably by the choice of extensometer, particularly under tensile loading, that leads to a distinct mode of localized deformation/transformation. Under compression-shear loading, inhomogeneous deformation (without lateral growth of martensite bands) is observed. The effects of extensometer gauge length are thus less pronounced than in tension, yet systematic—they are rationalized by considering the relative impact of differently deforming regions.

Determination of Weld Metal Mechanical Properties Utilising Novel Tensile Testing Methods

2007 ◽  
Vol 7-8 ◽  
pp. 127-132 ◽  
Author(s):  
M. Kartal ◽  
Rafal M. Molak ◽  
Mark Turski ◽  
S. Gungor ◽  
Michael E. Fitzpatrick ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Weld Metal ◽  
Tensile Test ◽  
Weld Zone ◽  
Local Stress ◽  
Gauge Length ◽  
Image Correlation ◽  
Stress Strain ◽  
Strain Behaviour ◽  
Dic Technique

The aim of this study was to develop a method of extracting local mechanical properties from weld metal by strain mapping using the digital image correlation (DIC) technique. The feasibility of determining local stress-strain behaviour in the weld zone of a 316H stainless steel pipe with a girth weld was investigated by tensile tests of specimens machined from the pipe so that it contained the weld at its centre. The tensile test was recorded using a high resolution digital camera and the DIC technique was used to obtain the complete set of full field displacement maps during the tensile test. The local strain was calculated at every sub-region of 32×32 pixels, which enabled the local stress-strain behaviour for this region to be determined. Results from these tests show the variability of the elastic modulus, yield stress and UTS across the weld. To check the reliability of the technique, a set of micro tensile samples, with gauge length of 3.7mm and crosssectional area of 0.7×0.7 mm2, were machined from the various locations in and around the weld zone. The comparison of stress-strain curves determined from micro-samples to stress-strain curves from the corresponding locations within a larger more conventional tensile specimen shows reasonably good agreement.

scholarly journals A Hybrid Experimental-Computational Approach to Determine Constitutive Models for Hyperelastic Polymers

2019 ◽  
Author(s):  
Atefe Karimzadeh ◽  
Majid R. Ayatollahi ◽  
Bushroa A. Razak ◽  
Seyed S. R. Koloor ◽  
Mohd Y. Yahya ◽  
...  
Keyword(s):  
Constitutive Model ◽  
Hybrid Approach ◽  
Compressive Loading ◽  
Constitutive Models ◽  
Strain Curve ◽  
Polymeric Materials ◽  
Computational Approach ◽  
Compression Tests ◽  
Stress Strain ◽  
Hyperelastic Materials

A study on the selection of hyperelastic constitutive model for polymeric materials is performed using a hybrid experimental-computational approach. Bis-GMA polymer is used as a case study of hyperelastic material to describe the polymer characteristics by determining its Poisson’s ratio and its valid range of the hyperelastic stress-strain curves. These two parameters are then used to determine the hyperelastic constitutive model by using the hybrid approach. Several uniaxial compression tests along with their finite element simulations are implemented in a systematic way, to identify the polymer behavior under the compressive loading conditions. Nano-indentation experiments are conducted to verify the hyperelastic behavior of the polymer. The experimental and computational evidences confirm that the Poisson’s ratio of Bis-GMA is 0.40 and the appropriate hyperelastic constitutive model for this polymer is of a second order polynomial. It is shown that, the results can be used to determine the true stress-strain curve of hyperelastic materials.

Evaluation of local constitutive properties of Al2024 friction stir-welded joints using digital image correlation method

2020 ◽  
pp. 030932472098120
Author(s):  
A. Shahmirzaloo ◽  
M. Farahani ◽  
M. Farhang
Keyword(s):  
Mechanical Properties ◽  
Digital Image Correlation ◽  
Digital Image ◽  
Welded Joints ◽  
Local Stress ◽  
Image Correlation ◽  
Welding Parameters ◽  
Stress Strain ◽  
Friction Stir ◽  
Dic Technique

The intense applied thermal gradients during the welding process leads to the variation in the properties of the weld zone and its surrounding areas. In this regard, determining the local mechanical properties and evolved microstructures of the weld and its surrounding zones are essential in the evaluation of welded structures. In this study, the local mechanical properties of Al2024 friction-stir-welded joints were precisely examined. Digital image correlation (DIC) technique using uniform stress (USM) and virtual field methods (VFM) were utilized to evaluate the local mechanical properties. The local stress-strain curves were plotted for different weld regions using local strain from the DIC technique. It was observed that the advancing side of the thermo-mechanically affected zone (TMAZ) had the lowest values of Young’s modulus and yield strength (YS), approximately 9% and 31% of the base metal, respectively. Effects of welding parameters, such as tool rotational and traverse speeds, were also taken into account. The plotted local stress-strain curve for the fractured region of welded specimens at lower rotational speed illustrated a higher strength and elongation. Furthermore, lower rotational and also higher traverse speeds resulted in the reduction of the grain size.

scholarly journals Anti-Inflammatory Properties of Injectable Betamethasone-Loaded Tyramine-Modified Gellan Gum/Silk Fibroin Hydrogels

Biomolecules ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 1456
Author(s):  
Isabel Matos Oliveira ◽  
Cristiana Gonçalves ◽  
Myeong Eun Shin ◽  
Sumi Lee ◽  
Rui Luis Reis ◽  
...  
Keyword(s):  
Rheumatoid Arthritis ◽  
Mechanical Properties ◽  
Silk Fibroin ◽  
Therapeutic Efficacy ◽  
Composite Structures ◽  
Gelation Time ◽  
Polymeric Materials ◽  
Gellan Gum ◽  
Traditional Use

Rheumatoid arthritis is a rheumatic disease for which a healing treatment does not presently exist. Silk fibroin has been extensively studied for use in drug delivery systems due to its uniqueness, versatility and strong clinical track record in medicine. However, in general, natural polymeric materials are not mechanically stable enough, and have high rates of biodegradation. Thus, synthetic materials such as gellan gum can be used to produce composite structures with biological signals to promote tissue-specific interactions while providing the desired mechanical properties. In this work, we aimed to produce hydrogels of tyramine-modified gellan gum with silk fibroin (Ty–GG/SF) via horseradish peroxidase (HRP), with encapsulated betamethasone, to improve the biocompatibility and mechanical properties, and further increase therapeutic efficacy to treat rheumatoid arthritis (RA). The Ty–GG/SF hydrogels presented a β-sheet secondary structure, with gelation time around 2–5 min, good resistance to enzymatic degradation, a suitable injectability profile, viscoelastic capacity with a significant solid component and a betamethasone-controlled release profile over time. In vitro studies showed that Ty–GG/SF hydrogels did not produce a deleterious effect on cellular metabolic activity, morphology or proliferation. Furthermore, Ty–GG/SF hydrogels with encapsulated betamethasone revealed greater therapeutic efficacy than the drug applied alone. Therefore, this strategy can provide an improvement in therapeutic efficacy when compared to the traditional use of drugs for the treatment of rheumatoid arthritis.

scholarly journals A General Temperature-Dependent Stress–Strain Constitutive Model for Polymer-Bonded Composite Materials

Polymers ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 1393
Author(s):  
Xiaochang Duan ◽  
Hongwei Yuan ◽  
Wei Tang ◽  
Jingjing He ◽  
Xuefei Guan
Keyword(s):  
Composite Materials ◽  
Constitutive Model ◽  
Model Parameters ◽  
Temperature Dependent ◽  
Stress Strain ◽  
Proposed Model ◽  
Single Temperature ◽  
Testing Data ◽  
Bonded Composite ◽  
Tension And Compression

This study develops a general temperature-dependent stress–strain constitutive model for polymer-bonded composite materials, allowing for the prediction of deformation behaviors under tension and compression in the testing temperature range. Laboratory testing of the material specimens in uniaxial tension and compression at multiple temperatures ranging from −40 ∘C to 75 ∘C is performed. The testing data reveal that the stress–strain response can be divided into two general regimes, namely, a short elastic part followed by the plastic part; therefore, the Ramberg–Osgood relationship is proposed to build the stress–strain constitutive model at a single temperature. By correlating the model parameters with the corresponding temperature using a response surface, a general temperature-dependent stress–strain constitutive model is established. The effectiveness and accuracy of the proposed model are validated using several independent sets of testing data and third-party data. The performance of the proposed model is compared with an existing reference model. The validation and comparison results show that the proposed model has a lower number of parameters and yields smaller relative errors. The proposed constitutive model is further implemented as a user material routine in a finite element package. A simple structural example using the developed user material is presented and its accuracy is verified.

Sign in / Sign up

Export Citation Format

Share Document