Patent Application
20240006033
The present invention refers to a predictive method for the dynamic properties of rubber compounds that is based upon machine learning, to be implemented therefore by means of an electronic computer, for the development of composites for tire tread compounds.
The present invention is in the tire manufacturing sector, in particular with reference to the determination of the composition of those rubber compounds used for manufacturing tire treads.
The dynamic properties of these rubber compounds (for example tan δ and E′) play a key role in determining tire performance, especially those that relate to energy dissipation (for example wet braking, dry braking and the Coefficient of Rolling Resistance (RRC).
These properties are ensured by the characteristics of the recipes used for the composites, in particular in terms of the ingredients, the quantity thereof and the particular synergies that are established between two or more thereof.
Commonly, the correct formulation of the recipes used for composites must go through several validation steps in the laboratory in order to first find the right technological package and then optimize the formulation by means of progressive fine-tuning until the objective is fully achieved.
Each of these iterative experimental campaigns leads, from the product point of view, to an increase in lead-times and costs in developing the product (time to market) and, from the data point of view, to the generation of a database with intrinsic variability due to random noise within the measurements made during the various test campaigns.
The expectations for the performance of the product, in relation to energy dissipation (for example wet braking, dry braking and RRC), is determined by evaluating the dynamic properties of the rubber compound (for example tan δ and E′). Such an evaluation requires extensive laboratory testing in order to reach validation of the composite and requires time and resources.
The object of the present invention is, therefore, to solve those problems left unresolved by the prior art, by providing a process as defined in claim 1.
In particular, an object of the present invention is that of simulating laboratory tests, in order to provide an accurate estimate of some of the significant dynamic properties of composites for the production of rubber compounds for tires without the need to perform any physical tests. These properties are, for example, tan δ and E′, which represent key parameters to determine the performance of those products that are associated with energy dissipation (for example wet braking, dry braking and RRC).
Further characteristics of the present invention are defined in the corresponding dependent claims.
On the other hand, the use of a software tool that can predict the behavior of composites, and therefore tire performance, allows for:
Other clear advantages over the prior art, together with the characteristics and usages of the present invention, will become clear from the following detailed description of the preferred embodiments thereof, given purely by way of a non-limiting example.
Reference will be made to the drawings in the attached figures, wherein:
The present invention will be described below with reference to the above figures.
A methodology will therefore be described for the prediction of dynamic properties (for example Tan δ and E′) of composites that can be used for the production of rubber compounds for tires.
In general terms, the process involves the following procedure:
In particular, after a step of training the model using the dataset contained in the normalized and pre-processed database as described above, it is possible to predict the dynamic properties of the composite with greater precision than by directly applying an algorithm straight to the raw data in the database.
In fact, in this way, it is possible to drastically reduce the effect, on the predictive precision, of database noise and the intrinsic variability of the data.
In fact, by means of the procedure for the iterative normalization of the data, operating by means of data relating to multiple laboratory tests on the same species of reference (at least one of the MN compounds present in each of the N experimental sessions), the aim is to reduce the intrinsic experimental variability. Indeed, each repeated test, performed during specific experimental sessions, is used to estimate the rate of variability due to these specific experimental conditions.
Furthermore, the pre-processing procedure (Data Mining) is used to improve the accuracy of predictions by developing new capabilities, removing aberrant data and performing a principal component analysis (PCA).
Finally, the machine learning algorithm, for example an artificial neural network (ANN), predicts some of the main dynamic properties of the composites under examination, for example, as already indicated, the tan δ versus temperature trend and the E′ versus Temperature trend.
During the dynamic mechanical analysis (DMA), a sinusoidal force (stress σ) is applied to a material and the resulting displacement (deformation) is measured. If the material is perfectly elastic, the resulting tension and stress are perfectly in phase. If the material is purely a viscous fluid, a 90 degrees' deformation phase lag, with respect to stress, is observed.
Viscoelastic polymers have intermediate characteristics whereby some phase delays occur during DMA tests. In this context:
The results are validated by comparing the values of tan δ and E′, as predicted by the developed algorithm, with those known experimentally for a plurality of new experimental recipes, which were obviously not used to feed the neural network (ANN) during the training step.
It should be noted that, according to the invention, important preprocessing steps are performed before the ANN algorithm training step. More specifically, the aforementioned data normalization procedure +the preprocessing step by means of data mining.
This normalization procedure has demonstrated the most efficient improvement. In this type of application, due to the repeated experimental sessions, it is usually possible to observe high variability as regards the target properties. Indeed, some recipes are often repeated in several experimental sessions and the target properties thereof sometimes demonstrate significant differences. By investigating all of the N experimental sessions performed, it is possible to find different recipes, amongst the MN possible recipes, that can be used to reduce this variability in relation to the experimental sessions.
The normalization is carried out on each experimental session by referring to those physical properties of the recipe that are common to the various experimental sessions. If such a recipe cannot be used to normalize some of the experimental sessions, insofar as it is not included in them, a new recipe will be selected, in such a way that it is included in at least one already normalized experimental session and in those experimental sessions still to be normalized. By means of this selection it will be possible to iteratively extend and apply the normalization to new experimental sessions.
From a mathematical point of view, these connections can be made in many ways and therefore different normalization procedures can be used.
According to the invention, each target property (i.e., for example, tan δ and E′) is divided by those corresponding to the recipes used as a reference in the experimental sessions.
From an operational point of view, the iterative normalization procedure is performed as follows:
It is important to highlight that, according to the invention and contrary to what happens in the known art, data normalization is not applied to the data set as a whole. The normalization procedure is applied in a specific and targeted way to each experimental session, and is developed in order to make each individual experimental session comparable to the others, thereby forming the data set as a whole. This objective is achieved by reducing the variability in relation to the experimental session. This means that what is generally discouraged in the known art, insofar as it introduces harmful non-linearities, namely the normalization of different data sets in different ways, according to the invention is used and exploited in order to achieve the desired results by means of the implementation of iterative normalizations that are determined according to the connections of the graph in
The normalization procedure can be described as:
wherein: i stands for i-th experimental session, j stands for the j-th example belonging to the specific experimental session, k stands for the k-th target property, ref, indicates the reference example of the i-th experimental session and
The following Table 1 shows the difference between performing the data normalization procedure or not in terms of accuracy.
In doing so, accuracy is defined as the percentage of recipes that show a percentage prediction error that is lower than the target percentage error. The E′ value prediction model showed an increase in accuracy greater than 30% by virtue of the application of the data normalization procedure (see the DELTA column), while the tan δ value prediction model showed an increase in precision greater than 11%.
This table shows the predictive precision of E′ and tan δ with the aim of highlighting the impact of the data normalization procedure. Normalized data processing improves the predictive performance of each individual target property. Interestingly, the normalization procedure introduces a 40% improvement in the prediction accuracy of E′ @ 0° (from 28.57% accuracy without normalization to 68.57% accuracy with normalized data).
The accuracy of the prediction is greatly improved when a correct data mining operation (iterative normalization, aberrant data removal, PCA) is performed on the experimental dataset used to build the algorithm during the “training step”. Indeed, PCA is able to remove those ingredients that do not affect the target properties (for example tan δ and
E′) from the recipes of the training dataset and to add new fictitious ingredients, created specifically in order to emphasize the informative content of the dataset.
With the term informative contribution of a feature (and therefore, by extension, of the dataset) reference is being made to the fact that the effect thereof upon the physical properties being predicted is well interpreted by the model, again in relation to the quantity and interaction thereof with other ingredients, in line with the performance thereof. A correct increase of 2 M pa in relation to one property of those in question following an increase-decrease of a certain ingredient is a ratio that, if properly interpreted by the model, is a positive informative contribution.
The anomalous data removal procedure is designed to be implemented by taking into account both each individual experimental session alone and all of the various experimental sessions jointly. This dual nature of the procedure makes it possible to take advantage of every single session.
In order to add new fictitious ingredients, with the aim of facilitating the subsequent creation of predictive models, the original ingredients have been divided into certain categories, i.e., polymers, fillers, accelerators, etc. PCA was then applied to each ingredient category in order to estimate a new fictitious ingredient that could enhance the informative content of that particular ingredient category. In this context, therefore, it is possible to define as a fictitious ingredient a linear combination of the actual ingredients, as supplied to the PCA, that is such that it can emphasize the informative contribution of that specific category of ingredients. This linear combination therefore combines the informative contribution of the initial ingredients. From this it follows that the informative contribution made by the fictitious ingredient summarizes and amplifies the informative contribution of the initial ingredients. Finally, for each category of ingredients, the fictitious ingredients determined in such a way have been added to the input list (i.e., ingredients) that the prediction algorithm has the task of processing and, therefore, both the original informative contributions and those amplified in the fictitious ingredient are subject to analysis.
Refer now to
In particular, the predictions become more reliable when the model is forced to simultaneously satisfy the following significant physical constraints:
wherein
and y stand for E′ and tan δ respectively.
The factor Ri°/j° is introduced in order to normalize the target functions tan δ (t) and E′(t). The normalization Ri°/j° is a necessary condition in order to ensure that the algorithm applies an equal “weight” to all temperatures, although the absolute values of tan δ (T) and E′(T) decrease. These constraints are applied by means of a weight/penalty logic to the cost function to be minimized during the training of the model itself. This means that the cost function is conveniently multiplied by:
Although both methodologies (with and without constraints) correctly predict the decay tendency of tan δ versus temperature, only the constrained model correctly estimates the increase in tan δ with an oil content.
The following Table 2 shows the prediction of the oil content on tan δ versus Temperature. Four materials were studied (A, B, C, D). The first lines show the recipes, in which the CPD column reports the formulation (from NR to RAE OIL) for the four materials (A, B, C, D). The middle rows indicate the predicted tan δ values, obtained by using a constrained model, while the last middle rows indicate the predicted tan δ values, obtained by using an unconstrained model.
The present invention has heretofore been described with reference to the preferred embodiments thereof. It is intended that each of the technical characteristics implemented in the preferred embodiments described herein, purely by way of example, can advantageously be combined, in ways other than that described heretofore, also with other characteristics in order to give form to other embodiments which also belong to the same inventive nucleus and that all fall within the scope of protection afforded by the claims recited hereinafter.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102020000029054 | Nov 2020 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/083492 | 11/30/2021 | WO |
