Measure Strength Of Carbon Fiber Reinforced Plastic

Carbon Fiber Reinforced Plastic or Carbon Fiber Reinforced Polymer (CFRP) is known for its high strength to weight ratio, excellent high-temperature characteristics and resistance fatigue. CFRP has gained substantial interest in manufacturing industries especially in the weight-critical aerospace industry. Also, it has applications in automotive, marine and civil engineering industries.

Carbon fiber is the backbone of CFRP and is responsible for its strength. Each carbon fiber is a long thin strand made of thousands of carbon filaments with a diameter of 5-10μm. The compressive strength of carbon fiber is significantly less than its tensile strength. Thus, in industry applications, axial compressive strength is usually used as the basis for its design rating. This ensures the safety and functionality of the finished product.

The FISCHERSCOPE® HM2000 (Fig. 1) is an automated instrumented indentation measuring instrument which is ideal for performing compressive strength testing on carbon fiber using a special 50μm Flat Indenter (see Fig.1). The FISCHERSCOPE® HM2000 is known for its high resolution and precision which is ideal for measuring small and brittle samples such as carbon fibers.

FISCHERSCOPE® HM2000 (left) with microscopic view of Flat; Indenter (right).

The FISCHERSCOPE® HM2000 is intuitive and does not require special specimen preparation for such tests. Simply place the CFRP sample on the measuring stage, check the monofilament diameter, and start the measurement.

The graph below (Fig. 2) shows the carbon fiber measurement process. As the indenter contacts the surface of the carbon fiber, the load increases linearly. Once the sample is crushed, the load curve gradient will increase rapidly. This occurred at a test force of 1547mN and compression (indentation depth) of 3.6 μm (see detail X in Fig. 2) for this sample. This force value is used to calculate the effective stress of the fiber in terms of compression. The microscopic images in Fig. 3 shows fragments of the remaining fiber after the fiber is fully crushed.

Graph showing Test force [mN] against Compression (Indentation depth [μm]).

Microscopic picture of the the small fiber before (left) and after the indentation (right).

Measure Mechanical Properties of Lacquer

In the automotive industry paint coatings are used as protection from corrosion and external damage. These lacquers are exposed to environmental influences such as extreme temperature fluctuations or moisture and salt. In addition, automotive coatings must exhibit a certain toughness to make them resistant to stone chips and scratches, for example in car washes. This requires the right balances between hardness and elasticity.

Car paint has to fulfill different functions and possesses therefore various properties. A quick differentiation and determination of its properties is possible with the characteristic parameters obtained from the instrumented indentation test.

The Martens hardness (HM) and the Martens hardness after creeping (HMCR) are values which specify plastic and elastic properties of the paint coating. The indentation hardness (HIT) considers only the plastic portion of the material deformation. The hardness parameters provide conclusions about aging, curing, cross-linking, embrittlement through UV radiation, hardness change through temperature influences and the degree of polymerisation of the lacquer.

Weathering rack in Florida of the company Atlas with various car body parts.

One of the most important advantages of the instrumented indentation test is the determination of elastic properties. Parameters like the modulus of indentation (EIT), elastic recovery (hIT), creep at maximum load (CIT 1) and creep at minimum load (CIT 2) can be detected using this method. The parameters described above allow various conclusions regarding visco-elastic properties of lacquer coatings. These in turn show the vulnerability of the lacquer against weather influences, its susceptibility to rockfall, the ability to heal in case of scratches and the reflow behaviour.

SAMPLE HM [N/MM²] HIT [%] C IT 1 [%] C IT 2 [%] E IT [KN/MM²]
A (mean) 42.9 23.4 18.4 -10,6 1,39
STD 1.2 0.8 0.2 0.3 0.1
B (mean) 143 45.7 6.1 -9 3.07
STD 5.6 0.4 0.1 0.3 0.1

Martens Hardness plot and plastic and elastic measurement parameters for 2k automotive repair paints; A being a soft sample and B a hard one

Using the FISCHERSCOPE® HM2000 makes the determination of material characteristics like surface hardness, crosslinking, elastic modulus and healing behaviour in case of scratches simple and easy. In this manner, several chemical process parameters can be determined quickly during manufacturing or hardening of automotive paint coatings. Your local FISCHER representative will be happy to answer further questions.

HM2000

Nanoindenter with programmable XYZ stage for automated measurements in the load range of 0.1-2,000 mN

Get More Information

Nanoindentation for DLC Coatings on Engine Components

Testing the Hardness of Thin DLC Coatings with FISCHERSCOPE® HM2000

In order to reduce emissions in combustion engines without sacrificing performance, manufacturers are continually working to improve the ability of the moving parts (e.g. camshafts, piston rings and gears) to resist abrasion and reduce friction. Coating them with DLC (diamond-like carbon) is just such an optimization. DLC coatings are not only very hard but also feature a certain toughness – which are two of the critical parameters that must be monitored during the coating process.

Composed primarily of amorphous diamond and amorphous graphite, DLC coatings serve first and foremost as protection against wear and tear but they also minimize friction. Due to their dark colour and the miniscule size of the indentation, determining their hardness by optically measuring the indenter impression is almost impossible and therefore unreliable.

A more accurate method for testing DLC coatings is nanoindentation, during which the force and displacement are continuously measured during both the loading and unloading phases. From these data, one can calculate the hardness and other quality-determining characteristics, such as the modulus of indentation. This method also prevents the substrate material from exerting any influence on the measurement results.

In this example, the measurement results of a 3 µm thick DLC layer are presented, as determined using the FISCHERSCOPE® HM2000. The Martens hardness (HM) takes the plastic and elastic deformation of the sample into account. The modulus of indentation (EIT), however, also allows conclusions to be drawn regarding the elastic behaviour. The values for penetration hardness (HIT) and the resultant converted Vickers hardness (HV) indicate the plastic properties of the samples.

DLC COATING HM N/MM² EIT/(1-VS^2) GPA HIT N/MM² HV
X 8442.98 173.71 19398.17 1833.13
s 785.22 15.89 2320.85 219.32
V/% 9.3 9.15 11.96 11.96

Martens hardness (HM) and other parameters of the DLC coating. The table shows the mean value, standard deviation and coefficient of variation of 12 measurements; the graph shows the depth-dependent profile.

The standard deviations and coefficients of variation illustrate the accuracy with which these quality-related parameters can be determined, even on rough samples with thin coatings. But the FISCHERSCOPE® HM2000 also makes it simple to take these highly sophisticated measurements:

  • Extremely fast sample preparation
  • Short measuring times
  • High depth resolution
  • Minimal, thus negligible, device compliance

When it is utterly crucial to determine the mechanical properties of DLC coatings with speed, accuracy and precision, the FISCHERSCOPE® HM2000 is indispensable. For further details, please contact your local FISCHER representative anytime.

FISCHERSCOPE® HM2000 AND HM500 NANOINDENTERS

Automatic and manual stage Nanoindenters with the load range of 0-2,000mN