Characterisation of the mechanical and fracture properties of a uni-weave carbon fibre/epoxy non-crimp fabric composite.

A complete database of the mechanical properties of an epoxy polymer reinforced with uni-weave carbon fibre non-crimp fabric (NCF) is established. In-plane and through-the-thickness tests were performed on unidirectional laminates under normal loading and shear loading. The response under cyclic shear loading was also measured. The material has been characterised in terms of stiffness, strength, and failure features for the different loading cases. The critical energy release rates associated with different failure modes in the material were measured from interlaminar and translaminar fracture toughness tests. The stress-strain data of the tensile, compressive, and shear test specimens are included. The load-deflection data for all fracture toughness tests are also included. The database can be used in the development and validation of analytical and numerical models of fibre reinforced plastics (FRPs), in particular FRPs with NCF reinforcements.

Specifications Table

Value of the data

This data set presents a complete mechanical characterisation of a CFRP system.

The data can be used as input properties in analytical models.

The data can be used as input parameters in finite element analyses and used for validation of results.

The data can be compared to already available data for others CFRPs. The data can also be used in the development of future CFRPs, in particular those with NCF reinforcements.

Guidelines for the mechanical and fracture characterisation of a given FRP material are provided.

Data

The stress–strain curves under the following loading cases are presented:

in-plane longitudinal tension

in-plane longitudinal compression

in-plane transverse tension

in-plane transverse compression

through-the-thickness (TT) tension

TT compression

in-plane shear

TT shear

The following terminology is used: 1-index refers to the longitudinal (to the fibre) direction in the reinforcement plane, 2-index refers to the transverse direction in the reinforcement plane, and 3-index refers to the TT direction w.r.t. the reinforcement plane. The stiffness and strength values are extracted from the stress–strain curves, and the specimen failure features reported.

Load–deflection curves are obtained from interlaminar fracture toughness tests in mode I, mode II and mixed-mode, and from translaminar fracture toughness tests. The energy release rates associated with the initiation of crack growth for the different tests are reported, as well as the crack resistance curves (R-curves).

The dimensions of the tests specimens are reported in Appendix A. The raw data for all test specimens are provided in CSV files in Appendix B.

2. Materials

The carbon fibre reinforced plastic (CFRP) material system is an HTS45/LY556. The Hunstman LY556 epoxy resin was supplied by ABIC Kemi AB. The reinforcement layer is a 205 GSM uni-weave non-crimp fabric (NCF), from Porcher Industries. It consists of HTS45 E23 Tenax® carbon fibre bundles, which are held together by glass fibre/polyamide weft threads (Fig. 1). HTS45/LY556 laminates were manufactured by resin transfer moulding (RTM) and vacuum infusion (VI) processes, according to the epoxy resin manufacturer׳s recommendation. All the test specimens needed to build the data set were prepared from the laminates listed in Table 1. The fibre volume fraction (FVF) was estimated from the laminate thickness, the laminate layup, the area weight of the carbon fibres in the NCF, and the density of carbon fibres (data provided in [1], [2]).

Fig. 1

Photograph of the uni-weave NCF.

Table 1

Plate specifications.

Plate	Layup		Thickness (mm)	FVF (%)	Manufacturing process	Cure+post-cure	Cure pressure (bar)
UD1	[0]10		1.83	61	RTM	4 h 80 °C+4 h 140 °C	3
UD2	[0]187		35/38	55/60a	VI	4 h 80 °C+4 h 140 °C	0.5
UD3b	[0]16		3.04	59	RTM	18 h 80 °C+4 h 140 °C	3
CP1		[0/90]5s	4.05	55	RTM	18h 80 °C+4 h 140 °C	3

Considering 35 and 38 mm for the laminate thickness.

7.5 micron polyimide film insert in the midplane of the laminate.

3. Experimental design and methods

In-plane tensile and compressive properties

The test procedure for the tensile and compressive in-plane tests followed the ASTM standard D 3039 [3] and the ASTM standard D 3410 [4], respectively. Both longitudinal and transverse properties were measured. All specimens were tabbed with 1 mm thick glass fibre/epoxy laminates and equipped with strain gauges. The compressive specimens were initially polished to eliminate free edge effects.

Table 2 and Fig. 2 report the results of the tests. The specimen bending in the gauge section, , was evaluated in the compressive tests from the back-to-back strain measurements, according to the standard recommendation (Eq. 2 in [4]). Only the average between the two strain gauge readings was considered to construct the stress–strain curve. In the tensile tests, the strain transverse to the loading direction was also measured to evaluate the Poisson׳s ratios of the FRP material.

Table 2

In-plane tensile/compressive properties.

Specimen	Modulus	Poisson ratio	Strength	Strain at failure	Fracture anglea	Bending, By (%)
Transverse	E_22c (GPa)		Y_c (MPa)	ε_22cu (%)	α_0 (deg)	(0.2%ε)		(ε_22cu)
compression	(0–0.3%ε)
cy1	9.4		118	1.48	65	−			−
cy2	8.5		114	1.47	53	2.2			-1.5
cy3	9.2		139	1.89	70	-0.5			2.4
cy4	9.7		140	1.79	64	2.5			7.5
cy5	9.7		133	1.78	56	3.5			8.5
cy6	9.0		138	1.88	65	5.6			3.8
Avg. (CV)	9.3 (5%)		130 (9%)	1.71 (11%)	62 (10%)
Longitudinal	E_11c (GPa)		X_c (MPa)	ε_11cu (%)		(0.2%ε)		(ε_11cu)
compression	(0.1–0.2%ε)
cx1	134		591	0.45		3.8			3.6
cx2	137		703	0.53		6.4			14.0
cx3	135		579	0.43		-6.8			6.5
cx4	129		572	0.43		3.8			1.8
cx5	127		649	0.52		4.6			11.4
cx6	130		690	0.55		-26.2			29.5
Avg. (CV)	132 (3%)		631 (9%)	0.49 (11%)
Transverse	E_22t (GPa)	v_21 (–)	Y_t (MPa)	ε_22tu (%)
tension	(0.05–0.2%ε)	(0.05–0.2%ε)
ty1	9.6	0.032	27.8	0.29
ty2	9.6	0.027	28.8	0.32
ty3	7.8	–	30.3	0.36
ty4	–b	–b	29.3	–b
ty5	8.8	–	29.7	0.33
Avg. (CV)	9.0 (10%)	0.029 (12%)	29.2 (3%)	0.32 (9%)
Longitudinal	E_11t (GPa)	v_12 (–)	X_t (MPa)	ε_11tu (%)
tension	(0.1–0.3%ε)	(0.1–0.3%ε)
tx1	129	0.23	1506	1.10
tx2	152	0.34	1889	1.23
tx3	146	0.25	1891	1.29
tx4	136	0.27	1851	1.25
tx5	137	0.33	1796	1.26
Avg. (CV)	140 (6%)	0.28 (17%)	1787 (9%)	1.23 (6%)

Defined in Fig. 3(d).

No strain reading.

Fig. 2

Stress–strain curves of the in-plane tensile and compressive tests; (a) longitudinal tension, (b) longitudinal compression, (c) transverse tension, and (d) transverse compression.

Longitudinal tensile specimens exhibited broom-like fracture, Fig. 3(a). Transverse tensile specimens failed in the gauge section at the end of the tabs, Fig. 3(b). Longitudinal compressive specimens failed by kink-band formation resulting in a stepped fracture surface, Fig. 3(c). Finally, transverse compressive specimens failed in a localised way with a smooth fracture surface oriented with an angle to the direction transverse to the loading, Fig. 3(d).

Fig. 3

Specimen failures observed in in-plane tests; (a) longitudinal tension, (b) transverse tension, (c) longitudinal compression, and (d) transverse compression.

Shear properties

Iosipescu tests, documented with the ASTM standard D 5379 [5], were performed to evaluate the material response under in-plane and TT shear (in the 1–3 plane) loading. The data was extracted from monotonic tests and cyclic tests. The latter consists of unloading/reloading cycles with an increasing level of applied load. The specimens were prepared with the fibres oriented along the specimen length. The specimens for in-plane shear testing were tabbed with a 1 mm thick glass fibre/epoxy laminate outside the notched region to increase their load bearing capacity. The material orthotropic ratios and were used to determine the opening angle of in-plane and TT shear specimens, according to the rescaling procedure proposed by Melin and Neumeister [6]. During the tests, the shear strain was determined by averaging strain measurements from the digital image correlation (DIC) system over a narrow band spanning the notch-to-notch axis of the specimen.

The failure mode of the Iosipescu specimens was premature failure at the notches by splitting, followed by shear failure in the gauge section (Fig. 4). This failure mode is described as an acceptable failure mode in the test standard [5]. The shear data, reported in Table 3 and Fig. 5, indicate that the shear strength of the material is close to the splitting stress of the specimen. In some specimens shear failure occurred prior to splitting failure.

Fig. 4

Failure of an in-plane Iosipescu specimen with the full-field strain measurements from the DIC system.

Table 3

In-plane shear and TT shear properties.

Test/specimen	Modulus	Strength	Strain at failure	Shear stress at splitting	Shear strain at splitting
In-plane shear	G_12 (GPa)	S_12 (MPa)	γ_12u (%)	(MPa)	(%)
(monotonic)	(0.2–0.4%γ)
xy1	4.8	79.8	11.3	74.1a	5.9a
xy2	4.5	79.0	9.2	76.2a	6.9a
xy3	4.1	75.7	7.4	75.7a	7.4a
xy4	4.2	76.8	8.7	72.0a	5.5a
Avg. (CV)	4.4 (7%)	77.8 (3%)	9.1 (18%)	74.5 (3%)	6.4 (14%)
In-plane shear	G_12 (GPa)	S_12 (MPa)	γ_12u (%)	(MPa)	(%)
(cyclic)	(0.2–0.4%γ)
xy5	4.2	72.2	11.1	68.5a	7.0a
xy6	4.5	73.3	10.1	66.1a	5.8a
xy7	4.2	74.8	11.4	69.0a	6.4a
xy8	4.3	71.8	9.3	69.3a	6.1a
Avg. (CV)	4.3 (3%)	73.0 (2%)	10.5 (9%)	68.2 (2%)	6.3 (8%)
TT shear	G_13 (GPa)	S_13 (MPa)	γ_13u (%)	(MPa)	(%)
(monotonic)	(0.2–0.4%γ)
xz1	3.8	59.4	3.4	59.3a	3.2a
xz2	3.9	54.5	2.6	51.2a	2.0a
xz3	3.5	53.3	2.2	52.0a	2.0a
xz4	3.4	59.8	3.2	59.8	3.2
xz5	3.9	56.4	3.0	56.4	3.0
Avg. (CV)	3.7 (6%)	56.7 (5%)	2.9 (17%)	55.7 (7%)	2.7 (24%)
TT shear	G_13 (GPa)	S_13 (MPa)	γ_13u (%)	(MPa)	(%)
(cyclic)	(0.2–0.4%γ)
xz6	−b	56.0	2.5	42.5a	1.4a
xz7	3.9	50.4	2.1	−	−
xz8	3.7	55.0	2.3	−	−
xz9	4.0	53.0	2.5	53.0	2.5
xz10	3.5	54.1	2.4	54.1	2.4
Avg. (CV)	3.8 (6%)	53.7 (4%)	2.3 (7%)	49.8 (13%)	2.1 (29%)

Stress and strain levels associated to the first split.

No load measurement in the range of modulus calculations.

Fig. 5

Stress–strain curves of the shear tests; (a) monotonic in-plane shear, (b) cyclic in-plane shear, (c) monotonic TT shear, and (d) cyclic TT shear. For the cyclic tests the entire response is shown for one specimen, and the envelopes of the stress–strain curves are shown for the other specimens.

Interlaminar fracture toughness properties

Double cantilever beam (DCB), end notched flexure (ENF) and mixed-mode bending (MMB) interlaminar fracture toughness tests are documented by test method standards [7], [8], [9]. A mode mixity of 0.5 was chosen for the MMB tests, i.e. . For tests involving a mode I component, hinge caps were used instead of the standard piano hinges. In all test setups, the crack elongation was measured from the specimen edge with a travelling microscope.

The critical energy release rates (mode I), (mode II), and (mixed-mode) were calculated following the procedure detailed in section 12.1.1 in [7], section 9.1 in [8], and section in 12.3.1 [9], respectively. From the load–deflection curves in Fig. 6, the initiation value of the critical energy release rates in each test was determined using the visual observation (VO), maximum peak (Peak), 5%/Max, and nonlinearity (NL) methods [7], [8], [9]. The critical energy release rate values at crack initiation for the different tests are reported in Table 4. The R-curves, in Fig. 6, were constructed using the VO method. For ENF tests, the crack generally made a single large jump as far as the loading point at the middle of the specimen, so no crack propagation value was measured. For the mode I tests, the R-curves in Fig. 6(a) are converging towards a propagation value of 300 J/m2.

Fig. 6

Load–deflection curves (left) and R-curves (right) obtained from (a) DCB tests, (b) ENF tests, and (c) MMB tests.

Table 4

Initiation values of the critical energy release rates from the interlaminar fracture toughness tests.

Test/specimen	Initiation value for the critical energy release rate (J/m2)
DCB (mode I)	VO		5%/Max	NL
dcb1	144		147	143
dcb2	143		143	137
dcb3	160		165	153
Avg. (CV)	149 (6%)		152 (8%)	144 (6%)
ENF (mode II)	VO	Peak
enf1	740	900
enf2	551	607
enf3	613	614
enf4	713	721
enf5	834	854
Avg. (CV)	690 (16%)	739 (18%)
MMB (mixed-mode)	VO	Peak	5%/Max	NL
mmb1	507	510	491	432
mmb2	179	476	304	304
mmb3	220	662	285	221
mmb4	122	603	246	199
Avg. (CV)	174*/257 (28/67%)	563 (15%)	332 (33%)	289 (37%)

Excluding deviant value of 507 for specimen. A possible explanation for the high toughness measured for specimen mmb1 is the presence of a rather uneven crack surface observed just at the location of crack initiation. The high energy built up at this location is finally released once a sufficient load is achieved, resulting in an instantaneous crack growth over 8 mm (see R-curve in Fig. 6(c)).

The fracture surfaces of DCB, ENF and MMB specimens were not perfectly flat but exhibited some waviness, which is specific of textile FRPs (Fig. 7). The formation of an undulating fracture surface is a toughness enhancing mechanism as it promotes slip-stick fracture processes.

Fig. 7

Crack path observed on a post-test MMB specimen. The initiation point indicates the end of the initial crack.

TT tensile and compressive properties

The TT tensile and compressive data were extracted using the double waisted specimen design proposed by Ferguson et al. [10]. A 1/2 scale version of the original specimen produces accurate data [10], but a 3/4 scale version was chosen to ensure that a sufficient amount of bundles of the NCF were present over the specimen gauge width (Fig. 8). The specimens were machined by a CNC milling machine using diamond-coated tools.

Fig. 8

Dimensions of the double waisted specimens.

Table 5 reports the material data extracted from the stress-strain curves of the tensile and compressive tests (Fig. 9).

Table 5

TT tensile/compressive properties.

Test/Specimen	Modulus	Poisson ratio		Strength	Strain at failure	Failure angle
Compression	E_33c (GPa)	v_32 (–)	v_31 (–)	Z_c (MPa)	ε_33cu (%)	λ_0 (deg)
	(0.4–0.7%ε)	(0.4–0.7%ε)	(0.4–0.7%ε)
cz1	7.7	0.43		204	5.03	56a
cz2	9.0	0.43		195	3.85	53b
cz3	7.9		0.02	206	3.50	54b
cz4	8.0		0.02	206	3.36	56a
cz5	7.9		0.02	203	3.34	52a
Avg. (CV)	8.1 (6%)	0.43 (0%)	0.02 (0%)	203 (2%)	3.81 (19%)	54 (4%)
Tension	E_33t (GPa)			Z_t (MPa)	ε_33tu (%)
(0.01-0.05%ε)
tz1	7.1			15.7	0.24
tz2	7.1			15.4	0.22
tz3	7.8			16.4	0.23
tz4	−c			13.1	−c
tz5	−c			13.0	−c
Avg. (CV)	7.3 (5%)			14.7 (11%)	0.23 (5%)

Failure mode B, according to Fig. 10(b). The average of the two fracture plane angles is used.

Failure mode A, according to Fig. 10(b).

No strain reading.

Fig. 9

Stress–strain curves of the TT tensile (a) and compressive tests (b).

For the compressive tests, the specimens were simply loaded between two parallel platens in displacement control equivalent to an initial strain rate of approximately 2%/min. Back-to-back strain measurements and stereo DIC measurements indicated no specimen bending. The strains were averaged from the DIC measurements over the entire surface of constant gauge section. The surface monitored by the DIC system was not always the same in all specimens so that the evaluation of both Poisson׳s ratios and was possible.

For the tensile loading configuration, rod end bearings were attached to the universal testing machine to prevent the introduction of moments in the specimens. The specimen end surfaces were adhesively bonded to two steel plates connected to the bearings. Strain gauges were bonded at the centre of the wider surfaces of the specimen, and the average of the two strain readings was considered to construct the stress–strain curves. In two specimens, the strain gauges produced inaccurate signals and the strain data were discarded. However, the strength values associated with these two specimens are considered reliable.

Fig. 10 shows the different specimen failure modes observed during testing. The adhesive bond remained intact in all tensile specimens, which fractured in a region close to the waist radius (Fig. 10 (a)). Two failure modes were observed in the compressive case, Fig. 10 (b), and a fracture angle, , was defined.

Fig. 10

Failure of the double waisted specimens; in tension (a), and in compression (b).

Translaminar fracture toughness properties

The test procedure described by Pinho et al. [11] was followed to determine the energy associated with fibre breakage in tension and in compression, using compact tension (CT) and compact compression (CC) specimens, respectively. Fig. 11 shows the geometry of the specimens. The machining of the notches was as follows: first a circular saw was used to make a wide cut, then a 0.5 mm wide notch was achieved using a precision low-speed saw (only for CT specimens), and finally a razor blade was used to create a sharp pre-crack. During testing, the load was introduced using steel cylinders through the holes of the CT/CC specimen.

Fig. 11

Dimensions of the CT specimens (a) and CC specimens (b); in mm.

Cross-ply specimens are needed to prevent splitting at the notch when the crack initiates. The data reduction scheme, based on Eqs. (1)(2), (3), was followed to extract the critical energy release rate for the 0°-plies in tension and in compression. In Eq. (1), the critical energy release rate for the laminate is calculated from the measurement of the critical load at crack initiation. is the thickness of each specimen. The unit energy release rate is found by calculating the J-integral of the specimen configuration (geometry and layup considered) with finite element methods.

From the critical energy release rate for the laminate, the critical energy release rate for the 0°-plies is found using Eqs. (2), (3), respectively,where is the total thickness of the 0°-plies, and the total thickness of 90°-plies. The values for and were taken from in Table 4. The results from the data reduction scheme are presented in Table 6.

Table 6

Initiation values of the critical energy release rates from the translaminar fracture toughness tests.

Test/Specimen	Initiation value for the critical energy release rate (kJ/m2)
Compact compression	G_Ic|lamcompressive	G_Ic|0°compressive
cc1	53.7	107.1
cc2	49.8	99.2
Avg. (CV)	51.8 (5%)	103.1 (5%)
Compact tension	G_Ic|lamtensile	G_Ic|0°tensile
ct1	32.3	64.1
ct2	35.2	70.0
Avg. (CV)	33.7 (6%)	67.1 (6%)

Subject area	Composite materials
More specific subject area	Material characterisation/mechanics of composite materials
Type of data	Table and graphs, pictures
How data was acquired	Universal testing machines, strain gauges (Showa N22-FA-5-120-11-VS2 for the in-plane tensile tests, Kyowa KFG-3-120-C1-11L3M3R for the compressive tests and through-the-thickness tensile tests), DIC system (ARAMIS 2M(-5M) from GOM GmbH), travelling microscope
Data format	Raw data in CSV format and post-processed data in tables and graphs
Experimental factors	Mechanical and fracture properties a uni-weave NCF composite material
Experimental features	Stress/strain response, stiffness, strength, fracture toughness, failure features
Data source location	Sweden
Data accessibility	Data are included in this article

Table 7

Information on the test specimens.

Specimen	Plate	Thickness (mm)	Width (mm)	Gauge length(mm)	Comments
Transverse compression
cy1	UD1	1.88	9.71	10.29	One strain gauge
cy2	UD1	1.93	9.77	10.70	−
cy3	UD1	1.93	9.78	10.89	−
cy4	UD1	1.94	9.87	10.46	−
cy5	UD1	1.92	9.81	10.74	−
cy6	UD1	1.95	9.72	10.45	−
Longitudinal compression
cx1	UD1	1.75	9.79	10.15	−
cx2	UD1	1.75	9.81	10.21	−
cx3	UD1	1.78	9.90	10.17	−
cx4	UD1	1.78	9.91	10.16	−
cx5	UD1	1.79	9.86	10.20	−
cx6	UD1	1.79	10.00	10.22	−
Transverse tension
ty1	UD1	1.80	25.00	125	−
ty2	UD1	1.80	25.00	125	−
ty3	UD1	1.83	14.95	-	One strain gauge
ty4	UD1	1.81	24.80	124	No strain gauge
ty5	UD1	1.87	24.20	122	One strain gauge
Longitudinal tension
tx1	UD1	1.80	11.99	90	−
tx2	UD1	1.80	12.02	90	−
tx3	UD1	1.81	12.02	90	−
tx4	UD1	1.80	12.04	90	−
tx5	UD1	1.80	11.96	86	−