Hi Mostafa,

Counterface definitely affects the wear behavior of materials. The characteristics of tribolayers (i.e. chemical composition, hardness, thickness, and the like) form during sliding are dependent on the type of counterface used. In addition, the hardness for different abrasive materials is not the same, and as a result, it influences the wear results achieved. As for differences of results reported in various studies, it might have different reasons, such as differences in humidity, tribometer design, the accuracy of controling systems for sliding velocity and applying load.

To make the wear condition more severe you can simply increase normal load or sliding distance.

Hope this helps,

Ahmad 

Hi Mostafa,

Counterface definitely affects the wear behavior of materials. The characteristics of tribolayers (i.e. chemical composition, hardness, thickness, and the like) form during sliding are dependent on the type of counterface used. In addition, the hardness for different abrasive materials is not the same, and as a result, it influences the wear results achieved. As for differences of results reported in various studies, it might have different reasons, such as differences in humidity, tribometer design, the accuracy of controling systems for sliding velocity and applying load.

To make the wear condition more severe you can simply increase normal load or sliding distance.

Hope this helps,

Ahmad 

Hello, Mostafa! Yes, I confirm the sentence of previous Colleague, that for increasing the wear loss you must to increase the normal load or time of trials. But if you want to increase sharply the wear loss you need use the abrasive surface.

You can increase normal load, time of testing and / or tangential speed between pin and disc in the contact zone.

The possibilities of intensification of wear process, however, is limited. We may obtain another type  (physical mechanism) of wear and the moment of this change is differ for various materials. You understand that factor makes the comparison of samples incorrect...There are some accellerated methods of tribotests  described in literature which take into account this circumstance.    

Thank you Ahmad, prof. Malyshev and Krahmer for your answers.

In some investigation wear rate of A356 were reported 80 mg with wear condition of:

Tangential speed= 0.5, normal load= 10 N, distance = 1800 m, and disc hardness =60

For my test I selected wear condition of

Tangential speed= 0.5, normal load= 30 N, distance = 8000 m, and disc hardness =60

but finally total wear rate of A356 was about 16 mg and I don't know why?

Mostafa: 

What you need to take into consideration is that what you measure by weighing the sample before and after wear testing is part of the sample which completely separates from the sample (i.e. the weight of debris). However, a considerable amount of the material removes from the sample's surface and accumulates at its edge during sliding. Even though this part of the sample is not on the surface anymore, it is weighed. 

I would suggest to measure the height of the sample before and after testing and multiply the difference of the heights by surface area to obtain volume loss. 

Wear and Material loss from a specimen should be regulated by the so called Archard Law that states

Vw=(K Fn L) / H

Where Vw= Wear Volume

K = constant adimensional

Fn = Normal Load

L = Sliding Distance

H = Hardness of the material

Anyway Archard Law is far from being an universal Law and presents several discontinuities and irregularities. It's rather a way for you to foresee the expected results inside a set of experiments.

Please don't forget the conductivity of the counterface which is an important factor in determining the contact temperature leading to an increase or decrease of the wear rate. 

Dear Mostafa

There are different variables you can use to increase the wear rate as it was previously mentioned in the above comments. Increasing the normal load and the sliding distance, have been by excellence the parameters commonly used to increased wear rate, but these parameters do not necessarily increase wear rate. For example, during pin-on-disk testing between some polymers (those who offer lubricity) against a harder counter part (i.e., steel), you only generate wear during the running-in of the test, once you achieved this stage, wear ceases. Based on the aforementioned explanation, more sliding distance will not increase wear rate and the intuitive concept of Archard equation (the higher the sliding distance the higher the wear rate) is no longer valid. There other different ways of increasing wear rate that are not based on Archard equation. For instance, you can change the geometry of the tribopair intending to cause yielding below the surface where wear wants to be measured. Reducing the diameter of the steel ball (pin) by one mm, while keeping the normal load constant, can change significantly the physics at the interface, resulting in more wear at the end of the test. The last suggestion is important if you take into account the fact that load transducers of most basic tribometers is very limited (in most commercial pin-on-disk tribometers is no more than 10 N), so that you can take advantage of the high Hertzian stresses induced, to cause more wear. However, this can be dangerous in the absence of lubricant, cause scuffing can be induced, and Archard equation will not longer be valid. I also suggest to check the literature, cause the initial surface roughness can help you to increase wear, but you have to be careful. I hope it helps 

Thank you all for your helps. Your comments are very helpful for me.

Mostafa,

Could you have adhesion based mass gain in your experiment, when compared to the another test, as you have higher load and longer distance?

Other possible reasons for the difference could be

-different disc material (though the hardness was same/similar)-temperature in the contact

-single pass or multi pass test, ie. was the sample going over new, untouched, surface for all the distance or was it going the same surface, already deformed surface after the previous passes

The weight, chemical composition, tribological properties are main parameters responsible.

Ofcourse the clarifications are acceptablebutWe  can't be describe a particular reason for increasing wear rate.There are multiple factors, combined effect of parameters and tribo pair properties,of course the environmental conditions.According to parametric conditions increasing applied load proportional to wear rate.But the sliding velocity not as like.The maximum of sliding  distance generate heat at the interface of the contact zone leads fatigue wear.It should be optimized for the various materials.

Dear Mostafa,

I fully agreed with all colleagues who expressed their opinions here, but let me try to express my considerations too.

You compare two wear conditions and they are ALMOST similar, although there are some differences and some uncertainties:

1. The distance of sliding is very different.

2. The normal load is different, and this may lead to significant difference in processes taking place in friction surfaces.

3. The material of counter body is unknown, although hardness is the same.

Just imagine the following:

You increase load from 10 N to 30 N and this changes wear mode. You also change sliding distance from 1800 m to 8000 m and therefore different wear stages may take place, including INCREASING mass of specimen because the material from counter body is transferred to your sample by some mechanism (this happen sometimes during friction stir welding for example). So finally you could have increasing the mass of your specimen if you increase sliding distance further :) So as you see your wear conditions are not similar and may by VERY different.

Regarding acceleration of wear test to increase wear loss – be very careful with this. It is known, that in some cases wear mechanisms may change dramatically with minor changing of testing parameters. I’d rather suggest you to find those testing conditions that correctly simulate your wear situation. Then try to accelerate wear, but very carefully to ensure that wear mode is not changed.

Please, check this question, I feel it may correlate with yours

https://www.researchgate.net/post/How_to_remove_BUE_from_the_surface_of_tool_before_tool_wear_measurement

Mostafa,

you also should take into consideration lubricating conditions, and types of lubricant used. 

Parameters including Sliding velocity, Sliding distance & time, load applied,  tribolayer properties, lubrication conditions if applicable, material of disc & pin, even humidity, plays much role in wear loss & wear rate.

ofcourse, the applied load ,sliding velocity and sliding distance matters a lot. In your case A356 if all the input paramaters are same, the reason for different wear rate may be due to surface roughness. More the surface roughness Higher the wear rate. U can  increase the wear rate by following parameters

1) PIN hardness should be more 

2) increase the load

3) increase the sliding time and sliding distance

4) disc roughness should be more 

Besides the loading parameters, lubricating as well as heat generation should also be considered.

Actually, it would be better if you described the wear rate as specific wear rate ( mm3/N-1m-1), exactly if u do so , you will find big difference. Moreover, the counterface material and the sliding conditions have great effect on the wear rate.

Refer the publication

Article Dry sliding wear behavior of SiC and B4C-reinforced AA6351 m...

High speed or high normal load that causes breaking of oxide film and hence increased wear. Beside these hardness of the specimen material, geometry (height and size of asperity), entrapping of wear debris particle in the contact region, time are the factors to be considered as well.