Elastic Work Factor Research Articles

Fracture behavior of seawater-absorbed carbon/epoxy laminated composites in the hydrostatic pressure condition

It was shown in the previous study that the fracture toughness of dried carbon/epoxy composites increased 38% as the applied hydrostatic pressure increased from 0.1 to 200 MPa. However, no research has been conducted on the fracture behavior of seawater-absorbed carbon/epoxy composites in a hydrostatic pressure environment. This work investigates the compressive fracture behavior of seawater-absorbed carbon/epoxy composites subjected to various hydrostatic pressures. Compressive fracture tests were performed under four hydrostatic pressure levels, 0.1 (atmospheric pressure), 100, 200, and 270 MPa. The compliance and fracture loads were determined from load–displacement curves as a function of hydrostatic pressure. Fracture toughness was determined from the elastic work factor approach. The results showed that compliance decreases but fracture load increases as the applied hydrostatic pressure increases. Fracture toughness increased with increasing pressure. Specifically, fracture toughness increased from 2.66 to 4.44 kJ/m 2, a 67% increase, as hydrostatic pressure increased from 0.1 to 270 MPa. Optical microscope examination of the fractured surface showed that local delaminations and microcracks are suppressed with increasing hydrostatic pressure. SEM examination showed that seawater-absorbed specimen shows a lot more epoxy fracture than the dried specimen.

Effect of Loading Rate on the Delamination Behavior of Carbon/Epoxy Laminated Composites

Previous studies show that fracture toughness of carbon/epoxy composite is affected by hydrostatic pressure. The fracture toughness of carbon/epoxy composite is also affected by strain rate. To date, no study has been made on the combined effects of hydrostatic pressure and strain rate on the fracture toughness of carbon/epoxy composite. This work investigates the compressive fracture behavior of carbon/epoxy composite subjected to low and high strain rates in the hydrostatic pressure environment. Compressive fracture tests were performed in the atmospheric pressure and hydrostatic pressure environment of 270MPa. The compliance and fracture load were determined from load-displacement curves as a function of applied strain rate. Fracture toughness was determined from the elastic work factor approach. The results showed that the compliance decreased as the applied strain rate increased. However, the fracture load is less affected by the strain rate. The toughness decreased with increasing strain rate. Specifically, for 270 MPa hydrostatic pressure environment, fracture toughness decreased from 4.64 kJ/m 2 to 4.05 kJ/m 2 (12.7% decrease) as the strain rate increased from 0.05% to 0.55%. The decrease of fracture toughness with an increase in the strain rate is due to the epoxy becoming brittle as there is not sufficient time for the stress to be relieved.

An Analysis for Arrest Toughness of Impact-Induced Delamination in Carbon/Epoxy Laminates

A model is proposed to identify an arrest toughness, which governs a delamination in laminates. Also, a statistical analysis is conducted to identify a variation of arrest toughness due to material nonhomogeneity. To these ends, impact and 3-point bending tests are performed on the Carbon/Epoxy laminates with various thickness. The fracture behavior can be described by a crack arrest concept. The arrest toughness can be evaluated by an elastic work factor. Also, the Weibull distribution is suitable to predict a failure probability for the arrest toughness. Moreover, the variation of toughness increase gradually with the increase of the specimen thickness. This behavior may be attributed to a change of material nonhomogeneity with the specimen thickness.

On the application of η-factor approach to determine compressive fracture toughness of fiber-reinforced composites under hydrostatic pressure environment

It was shown in the previous studies that the η-factor approach could be used to determine fracture toughness of fiber-reinforced composites in air environment. This work investigates the applicability of the η-factor approach to determine fracture toughness of thick graphite/epoxy composites in the hydrostatic pressure environment. The effects of hydrostatic pressure and stacking sequence on the elastic work factor were studied. The stacking sequences used were unidirectional, [0°] 88 and multi-directional, [0°/±45°/90°] 11s. The hydrostatic pressures applied for [0°] 88 case were 0.1, 70, 140, and 200 MPa. The hydrostatic pressures applied for [0°/±45°/90°] 11s case were 0.1, 100, 200, and 300 MPa. For each stacking sequence and hydrostatic pressure, the values of fracture toughness determined using the η-factor approach were compared with those determined from the compliance method. The results showed that the elastic work factor was not affected by the hydrostatic pressure and the stacking sequence. The elastic work factor decreased in a linear fashion with crack length. The results also showed that the values of fracture toughness determined from the η-factor approach are very comparable to those determined from the compliance method for each stacking sequence and hydrostatic pressure. Thus, fracture toughness of thick graphite/epoxy composites in the hydrostatic pressure environment can be determined from a single fracture test using the η-factor approach.

Effect of hydrostatic pressure on the elastic work factor, ηel and fracture toughness determination of unidirectional composites using ηel

Previously, fracture toughness of graphite/epoxy composites in the hydrostatic pressure environment was determined using the compliance method. However, it requires four to five test specimens of different crack lengths in order to determine fracture toughness. In this work, the elastic work factor approach was applied to determine fracture toughness of unidirectional (0°) thick graphite/epoxy composites from a single fracture test in the hydrostatic pressure environment. First, the effect of hydrostatic pressure on the elastic work factor was studied. Second, the fracture toughness determined using the elastic work factor approach was compared with that determined from the compliance method at each hydrostatic pressure level. The results showed that the elastic work factor was not affected by hydrostatic pressure, and it decreased linearly with delamination length. The results also showed that the values of fracture toughness determined from both methods were comparable to each other at each hydrostatic pressure.

Determination of Fracture Toughness, GC of Graphite/Epoxy Composites from a Cracked Lap Shear (CLS) Specimen

Previously, the work factor approach was applied to determine fracture toughness, Gc of unidirectional graphite/epoxy CLS specimen, and it is required to apply the approach to determine Gc of multi-directional CLS specimen. In this work, the elastic work factor, η el form of multi-directional CLS specimen was calculated numerically as a function of delamination length in order to investigate stacking sequence effect on η el. The calculated η el was applied experimentally to determine fracture toughness, G c of multi-directional ([0/±45/0] s/[02/±452/02] s, [0/±45/0] s/[02±452/902] s, and [902/02] s/[04/904] s for the lap and the strap) graphite/epoxy composites. For each case, the Gc values determined from the η el approach were compared with those determined from the compliance method. Numerical results show that η el is not affected by the fiber angles of plies, and η el is linearly related to delamination length. It was found from the experimental results that Gc determined from the η el approach is in a maximum 15% range of difference with that determined from the compliance method for each case. It was also found from the SEM examination that delamination propagated irregularly through interfaces of lap and strap (8th and 9th plies) for [902/02] s/[04/904] s case while no delamination transfer was observed for [0/±45/0] s/[02/±452/02] s and [0/±45/0] s/[02/±452/902] s cases.

An Analysis for Delaminations Using Energy Release Rate in CFRP Laminates

The understanding of impact-induced delamination is important in safety and reliability of composite structure. In this study, a model for arrest toughness is proposed in consideration of fracture behavior of composite materials. Also, the probabilistic model is proposed to describe the variability of arrest toughness due to the nonhomogeneity of material. For these models, experiments were conducted on the Carbon/Epoxy composite plates with various thickness using the impact hammer. The elastic work factor used in J-Integral is applicable to the evaluation of energy release rate. The fracture behavior can be described by crack arrest concept and the arrest toughness is independent of the delamination size. Additionally, a probabilistic characteristics of arrest toughness is well described by the Weibull distribution function. A variation of arrest toughness increases with specimen thickness.

Stacking sequence effect on the elastic work factor of a cracked lap shear composite specimen

Stacking sequence effect on the elastic work factor of a cracked lap shear composite specimen

$G_IC$ determination of unidirectional graphite /epoxy DCB composites from the elastic work factor approach

Compliance calibration method is frequently used to determine from the DCB composite specimen. However, the method requires at least 4 to 5 fracture test (loading-unloading) records. In this study, of unidirectional graphite/epoxy DCB composites was determined from the elastic work factor approach which uses a single fracture test record. In order to inspect the validity of the elastic work factor approach, determined from the elastic work factor approach was compared to that of determined from the compliance calibration method. It was shown that determined from the elastic work factor approach was comparable to that determined from the compliance calibration method. That is, the elastic work factor approach can be used to determine of unidirectional graphite/epoxy DCB specimen from a single fracture record.

On the validity of applying the elastic work factor approach to determine GIc of fiber-reinforced laminated composites

Previously, the elastic work factor, η el of a DCB specimen was derived from a simple bending theory. In this study, the η el derived from simple bending theory was compared with that calculated from a finite-element method. The η el derived from simple bending theory was applied experimentally to DCB specimens with two stacking sequences in order to determine G Ic of fiber-reinforced composites (AS4/3501). The stacking sequences used were [0] 16 and [ 0 2± 45 2 0 2 ] s . G Ic determined from the work factor approach was compared with that determined from the compliance method for each stacking sequence. The results showed that the work factor approach and the compliance method produce comparable results of G Ic for each stacking sequence. Thus, G Ic can be determined from a single DCB specimen using ν el derived from simple bending theory.

Elastic Work Factor of CLS Specimen and Determination of $G_c$ for Graphite/Peek Composites by Using the Elastic Work Factor

It was shown in the previous study that the numerically derived elastic work factor for CLS specimen was independent of fiber direction for a unidirectional case. Also, it was proposed the elastic work factor could be used to determine energy release rate from a single test record. In the present study, elastic work factor was derived from a simple beam theory to investigate its dependence on material property and geometric condition. Also, the elastic work factor of CLS specimen was applied experimentally to determine critical energy release rate in order to prove its validity determining critical energy release rate from a single specimen. For this purpose, critical energy release rate determined using the elastic work factor was compared with that determined by the compliance method. The results showed that while elastic work factor is affected by and it is independent of fiber angle for a unidirectional case. It was also found that critical energy release rates determined by both methods are comparable each other, thus elastic work factor approach can be used to determine energy release rate from a single test specimen.

Determination of Mode I Fracture Toughness of Fiber Reinforced Composites by the Elastic Work Factor

The work factor approach was applied to determine of fiber reinforced composites (AS4/3501) from a single unidirectional (0-deg) DCB specimen. Elastic work factors of DCB specimen for three different symmetrical staking sequences were derived from a simple bending theory and a finite element method. The results showed that elastic work factors calculated from both methods were comparable each other. In particular, the elastic work factor of DCB specimen with symmetrical stacking sequence is independent of stacking sequence. The determined from the work factor approach was compared with that determined by the compliance method. The results showed that the work factor approach and the compliance method produce comparable results of . Thus, can be determined from a single DCB specimen using the work factor approach.

Evaluation of elastic work factor for a double cantilever beam specimen

Evaluation of elastic work factor for a double cantilever beam specimen

A Study on the Application of Work Factor Approach to Composite Laminates

Static fracture tests using the cracked lap shear (CLS) specimens made of thermoplastic composite APC-2 were conducted to verify if the elastic work factor devel oped previously is a valid parameter to calculate energy release rate from a single speci men. Also, the elastic work factor was derived theoretically based on a beam analysis. The experimentally determined elastic work factor, (η el)exp was compared with those calculated from a beam analysis and a finite element analysis. The results showed that the elastic work factors determined from these three ways are comparable to each other. In ad dition, the elastic work factor was applied to determine a critical energy release rate, and it was found that the elastic work factor approach can be used to determine energy release rate from a single specimen.

Parametric studies on the elastic work factor for the CLS specimen

Parametric studies were conducted to see the effects of geometric conditions on the elastic work factor for the CLS specimen. Elastic work factors were calculated in two different ways: numerically using a finite element analysis and analytically from a beam analysis. The results showed that the elastic work factors determined from both methods are comparable. In addition, the results showed that the elastic work factor is not greatly affected by L 2 L 1 but is significantly affected by t 1 t 2 .

Method for Computing Energy Release Rate Using the Elastic Work Factor Approach

The elastic work factor ηel concept was applied to composite structures for the calculation of total energy release rate by using a single specimen. Cracked lap shear specimens with four different unidirectional fiber orientation were used to examine the dependence of nel on the material properties. Also, three different thickness ratios (lap/strap) were used to determine how geometric conditions affect ηel. The ηel values were calculated in two different ways: compliance method and crack closure method. The results show that the two methods produce comparable ηel values and while ηel is affected significantly by geometric conditions, it is reasonably independent of material properties for the given geometry. The results also showed that the elastic work factor can be used to calculate total energy release rate using a single specimen.