Process and apparatus for determining the infinitesimal-hardness behaviour of synthetic materials, coatings and ductive materials

Abstract

A process and apparatus for the rapid determination of the infinitesimal-hardness behaviour of plastic materials, coatings and ductile materials. The process is characterized in that there is employed the continual penetration at a narrowly defined location on a layer of an indentor for the continual recording of the therewith associated penetration depth, whereby this penetration by the indentor may take place in a normal or in a particularly formed atmosphere. In connection therewith, the penetration and, respectively, the loading sequence must be so controlled, whereby the sequence of the continually varying loads and the therewith associated continual penetration values may be digitally recorded in small incremental steps.

Description

FIELD OF THE INVENTION

The present invention relates to a process and apparatus for the rapid determination of the infinitesimal-hardness behaviour (IHV) of plastic or synthetic materials, coatings and ductile materials.

The IHV-process, as such, was first made public by the applicant in 1968 in Brussel, Belgium and, concurrently, an illustration of associated manually controlled apparatus and methods of evaluation. If, under normal penetration hardness-measurement, F defines the load under which an indentor, -pyramid-tip, shere, conical point and the like, penetrates into the upper surface of the material being tested to a penetration depth y, then these reciprocal relationships are normally represented by a diagram represented by the curves in FIG. 1, as discussed in datail hereinbelow. This type of curve, however, showed itself to be dependent upon the load time duration, the configuration and outer surface characteristics of the indentor and, for thin coatings and lacquer layers, additional dependence upon the thickness of the layer.

In lieu of characterizing the hardness of an outer surface by means of these curves, it has also been attempted to use the penetration surface for this purpose, in effect, circular or rectangular, which is left by the correspondingly shaped indentor after completion of the penetrating process. Thusly, the Brinell-hardness was expresses as H = F/A, wherein F designates the load, and A the penetration surface. However, this method of hardness measurement also evidenced the disadvantage of the above-mentioned parameter-dependencies.

The novel aspect of the IHV-process, however, lies in that the quotient F/y is recorded in dependence on the load F, as set forth in the curves persuant to FIG. 2, from which there similarly is obtained a parameter-dependent quotient curve. However, inasmuch as the crossing point of this curve with the ordinate axis forms a so-called boundary or limit-value, this particular boundary transition has been found to be parameter-independent to greatest possible extend. Consequently, this value has been characterized as a particularly distinguished value as the "IHV-value", having the equation

IHV = lim (F/y).sub.F.sub..fwdarw. 0

The foregoing represents an extremely significant value, which is singular for the material being utilized, with the value being varied in a characteristic manner through the conditions and minutest changes experienced by the material from external, frequently intended, influences. Extensive experiments and theoretical investigations have indicated that

IHV .about. C .sqroot. E

wherein

C = a finely variable value, dependent upon, the particular material and condition of the test object; and

E = the modulus of elasticity of the material of the test object.

The IHV-values thereby also encompass the interactions between, for example, pigment and plastic material interiorly of heterogeneous and quasi-homogeneous plastic material-matrices; interactions, which again lead to further results respecting the structure, build-up and relationships of the materials. The IHV-value is a decidedly outer surface value, which is, however, also determined in a certain degree by the immediate or contiguously adjoining lower layers. Since plastic material and coating outer surfaces react quite rapidly in response to external conditions, the IHV-value also immediately responds to changes in the exterior conditions of the plastic material, and the like. Such external conditions may be, for example, those of exterior weathering, artificial weathering, gas, steam and liquid applications, electrical, mechanical, magnetic and radiation conditions, and so forth. Thus, the artificial weathering may be effected in a suitable climatized chamber, or in a sealed climatized chamber containing the materials to be tested. The chamber may be heated so as to provide suitable temperature conditions. The teasting conditions may also be created through treatment of the materials with acid fumes, such as of inorganic acids, i.e. HCl, H.sub.2 SO.sub.4, HNO.sub.3, or organic acids such as HCOOH, CH.sub.3 COOH, ditric acid, lactic acid or chloracetic acid. The fumes or vapors may also be constituted of water, alcohol, esters, ethers, acetates, aromatic and aliphatic carbohydrates. Aggressive gases, such as SO.sub.2, HCl and HF may also be employed.

The electrical influences or effects for conditioning the materials may comprise high-frequency currents, light beams including infrared, ultraviolet, radioactive, X-ray and electron beams.

All of the aforementioned conditioning and afflicting elements may be used individually, collectively, or in various combinations, as required for the particular evaluation tests.

When a so-treated exterior surface is removed from the conditioning or treating zone, it builds back mostly quite rapidly, but not fully reversibly. Thereby it becomes advantageous to create possibilities which permit the test objects to also be measured also during the presence of these conditions.

DISCUSSION OF THE PRIOR ART

Heretofore, exterior weathering tests required durations of one to two years in order to provide definite results. Through the application of the rapid and sensitively reacting IHV-methods only hours, days or a few weeks are required therefor. In addition, it is not necessary to apply falsified elevated conditions which, for example, are impressed on the probes by means of the Weather-o-meter.

For reception of the measuring values leading to the IHV-value, heretofore there have been employed usual or known microhardness-indentation measuring apparatus such as, for example, the Wallace-Indentation-Tester, or the ICI-apparatus. The process entailed that a Vickers-pyramid subjected to variable loads was pressed into the plastic material being tested for a freely selected but constant time period, and in which the particular and time-constant penetration depth was measured or registered in dependence upon the particular load. However, from penetration to penetration, the test member had to be displaced for a minutely small distance, so as to avoid erroneous measurements caused by the previous measurement of the particular location. The predetermined loads and the thereby obtained penetration depth values were divided by each other, and the quotient F/y plotted on a Cartesian coordinate graph as functions of the loads F. The extrapolation of the limit-value F .fwdarw. O resulted by means of a regression curve through the quotient values F/y. The crossing point of the regression curve with the F/y -ordinates axis then provided the IHV-value.

SUMMARY OF THE INVENTION

The present invention eliminates the disadvantages encountered in the described prior art methods with numerous "manually effected" steps through improvement and acceleration thereof, while requiring a completely new concept for the obtention of the IHV-value.

Basically it must thereby be determined that there is provided a consistency in the values, which afford a new limit-transition toward the IHV-value. The inventive process is thereby characterized, in that there is employed the continual penetration at a narrowly defined location of an indentor for the continual recording of the therewith associated penetration depth, whereby this penetration by the indentor may take place in a normal or in a particularly formed atmosphere. In connection therewith, the penetration and, respectively, the loading sequence must be so controlled, whereby the sequence of the continually varying loads and the therewith associated continual penetration values may be digitally recorded in small incremental steps.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference may now be had to the following detailed description of the invention, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a graphical illustration showing the plot of load with respect to penetration depth for two coating thicknesses for a prior art penetration measurement;

FIG. 2 is a graphical illustration similar to FIG. 1 utilizing the IHV-process according to the present invention; and

FIG. 3 is a schematic view of an apparatus for effecting the IHV-process according to the present invention.

DETAILED DESCRIPTION

Referring to the drawings, the apparatus disclosed therein facilitates the application of the method by means of two alternatives:

Alternative (a):

The penetrating sequence of the indentor is effected without interruption at a continually increasing load, and the therewith associated penetration depths are thereby continuously digitally recorded and evaluated. A family of new curves (F/y, --F) is thus obtained which, in comparison with the curves from the previous methods, lies somewhat more elevated, but which must lead, on the basis of mathematical boundary transition concepts, to the same IHV-value. Such a recording with rapidly changing values is unthinkable for a manual peration, and positively retards the automation.

In order to effect the inventive concept, an apparatus constructed in accordance with the principle of FIG. 3 may be employed. IN the drawing, 1 defines the support for a probe 1a, 2 defines the indentor, 3 and 4 the control system for the indentor, which may be either electrical or mechanically and pneumatically operated, 4 and 5 comprise the recording means for the penetration depth of the indentor 2. The load values and the penetration depth values are amplified by, respectively, elements 6 and 8, and recorded through component 9, and from which there may be ascertained the balancing parabola and the crossing point with the F/y axis in a computerized manner. Component 7 symbolically illustrates the Zero-position-adjustment installation for the indentor, and similarly component 10 symbolically illustrates the power supply circuit for the apparatus.

Alternative (b):

This alternative is particularly suitable for application to materials having a low modulus of elasticity. In this instance, a method must be sought in which the penetrating process is braked, but will nevertheless still lead to a measurable limit-value. This may be attained in that there may be placed in opposition to the alternative a of steering the load of the penetrating indentor a larger continuous operation, which is to be handled in the material. This may be effected by constructing the indentor as a wheel having conically ground periphery, so that the object to be tested is moved in a translatory manner below this loaded wheel. The wheel may be formed as a starwheel, having peripheral wedge-shaped segments. In accordance with the type of material, F/y-- F curves are obtained which lie higher, but occasionally also lower, than the values obtained through the Alternative (a). The limit-value must coincide, however, when employing the same material for Alternatives (a) and (b), again due to the limiting requirements excluding boundary transition. Above all, the apparatus here becomes considerably complicated, since for the Alternative (a), there is still added the translation of Alternative (b).

While there has been shown what is considered to be the preferred embodiment of the invention, it will be obvious that modifications may be made which come within the scope of the disclosure of the specification.

Claims

What is claimed is:

1. In a process for determining the infinitesimal-hardness behaviour of plastic materials, in particular coatings and ductile materials, including penetrating a test material layer with an indentor in dependence upon a load exerted on the indentor; and recording the extent of penetration; the improvement comprising: continually effecting said penetration by said indentor in small steps at narrowly defined locations on said layer, concurrently and continually increasing the load on said indentor; operatively connecting a process calculator and computer to a portion of said indentor providing measurement values of the depth of penetration in dependence upon the load exerted on said indentor, said calculator and computer continuously recording depths of penetration y in dependence upon loads F exerted on said indentor, transforming this relationship into F/y-quotients, plotting a curve through these F/y-quotients in dependence upon loads F and determining the crossing-point with the F/y-ordinate axis so as to indicate the value of the Infinitesimal-Hardness-Behaviour IHV.

2. An improvement as claimed in claim 1, said process being effected under a normal atmospheric environment.

3. An improvement as claimed in claim 1, said process being effected in a climatized chamber.

4. An improvement as claimed in claim 1, comprising subjecting said test material to thermal conditioning, cincluding selective heating and cooling thereof.

5. An improvement as claimed in claim 1, comprising conditioning said test materials through climatizing preceding the penetration testing thereof; and imparting additive specialized conditioning to said test materials.

6. An improvement as claimed in claim 5, said specialized conditioning comprising mechanical treatment of said test materials.

7. An improvement as claimed in claim 5, comprising imparting said specialized conditioning to said test materials through the intermediary of acid fumes.

8. An improvement as claimed in claim 7, said acid fumes being one or more inorganic acids selected from the group consisting of HCl, H.sub.2 SO.sub.4 and HNO.sub.3.

9. An improvement as claimed in claim 7, said acid fumes being one or more organic acids selected from the group consisting of citrio acid, lactic acid and chloracetic acid.

10. An improvement as claimed in claim 7, comprising imparting said specialized conditioning to said test materials through the intermediary of solvent vapours, such as one or more in combination, water, alcohol, esters, ethers, acetates, aromatic and aliphatic carbohydrates.

11. An improvement as claimed in claim 7 comprising imparting said specialized conditioning to said test materials through aggressive gases, said gases being one or more gases selected from the group consisting of SO.sub.2, HCl, HF.

12. An improvement as claimed in claim 7, comprising imparting said specialized conditioning to said test materials through electrical and electromagnetic treatment, such as, high-frequency currents, light beams, infrared light, ultraviolet light, radioactive rays, and X-ray electron beams.

13. An improvement as claimed in claim 7, comprising concurrently imparting a combination of specialized conditioning treatments to said test materials.

14. An improvement as claimed in claim 1, said narrowly defined location on said layer comprising a single point of initial contact between said indentor and said testing material layer.

15. An improvement as claimed in claim 1, said indentor comprising a spherical penetration member.