This article presents a review of current methods for production of metallic open-cell porous materials through space holders. The methods are divided into two major groups: on the basis of sintering and using liquid phase processing. Details about technologies are given, and their relations to structure parameters of obtained materials are discussed. Methods with 11 different space holders are described. The space holders could be metallic or nonmetallic (organic and inorganic) materials which could be leached or burned depending on removal technique. It is concluded that the flexible application of different space holders offers opportunities for obtaining large variety of metallic porous structures. A new line of development should be elaboration of complex techniques for production of porous structure with graded pore size and/or porosity which will meet various engineering requirements and will open new possibilities for applications as functional and structural elements. The next part of this work is devoted to the structure, the properties, and application of the open-cells porous materials obtained through space holders.

This work presents an overview of structural characteristics and basic mechanical properties of the open-cell metallic foams obtained by different space-holder methods, which are discussed in Part I of the same review. The presentation is arranged with respect to foam material, and the structure and properties are compared for different space holders and production techniques. In order to have more clear information for the structures obtained and their relation with production techniques, many images are provided and discussed. Compressive behavior of the foams is shown, and stress–strain curves are analyzed with respect to the energy absorption characteristics. The analysis are made on the basis of different porosities and processing parameters. Some applications of the open-cell metallic foams are discussed in the end of the article.

It is well known that mechanical stimulation promotes indirect fracture healing by triggering callus formation. We investigated the short-term response of healing tissue to mechanical stimulation to compare the changes in tissue stiffness during stimulation and resting phases in a preclinical case-series. Four sheep underwent a tibial osteotomy and were instrumented with a custom-made active fixator which applied a mechanical stimulation protocol of 1000 cycles/day, equally distributed over 12 h, followed by 12 h of rest. During each cycle, a surrogate metric for tissue stiffness was measured, enabling a continuous real-time monitoring of the healing progression. A daily stiffness increase during stimulation and an increase during resting were evaluated for each animal. One animal had to be excluded from the evaluation due to technical reasons. For all included animals, the stiffness began to increase within the second week post-op. A characteristic pattern was observed during daily measurements: the stiffness dropped considerably within the first stimulation cycles followed by a steady rise throughout the rest of the stimulation phase. However, for all included animals, the average daily stiffness increase within the first three weeks post operation was larger during resting than during stimulation (Sheep I: 16.9% vs. −5.7%; Sheep II: 14.7% vs. −1.8%; Sheep III: 8.9% vs. 1.6%). A continuous measurement of tissue stiffness together with a controlled fracture stimulation enabled the investigation of the short-term effects of specific stimulatory parameters, such as resting periods. Resting was identified as a potentially determining factor for bone healing progression. Optimizing the ratio between stimulation and resting may contribute to more robust fracture healing in the future.

This research investigates the tribological behavior of advanced open-cell porous AlSi10Mg-SiC composites fabricated using the novel replication method of NaCl space holders. These composite materials have potential applications in lightweight and high-strength structures that require high resistance to friction and wear. The composites were tested using a pin-on-disk method under dry sliding-friction conditions at ambient temperature, with a sliding velocity of 1.0 m∙s⁻¹ and an applied load of 50 N. The resulting wear parameters, including the coefficient of friction (COF) and mass wear, provided quantitative measures of the tribological behavior. Microstructural observations of the worn composite surfaces were carried out using scanning-electron microscopy (SEM) to study the wear mechanisms, and an elemental analysis was performed using X-ray energy-dispersive spectroscopy (EDS) to examine the elemental composition. The results showed that the AlSi10Mg-SiC composites had lower mass wear and COF than the open-cell porous AlSi10Mg material under the same experimental conditions. Three different machine learning (ML) models were employed to predict the COF of the composites, and their performances were evaluated using the R2, MSE, RMSE, and MAE metrics on the validation and test sets.

In this study, a hybrid material is produced, and the effect of different loads varying from 40 to 60 N against an EN-31 steel counter disk on its wear behavior under dry sliding conditions at room temperature is studied. The tribological behavior is studied via the pin-on-disk method and analyzed using primary wear parameters, such as the coefficient of friction (COF), mass wear, and specific wear rate. The obtained results are compared with the results for B83 babbitt under the same wear test conditions. Microstructural observation with scanning electron microscopy (SEM) is performed along with X-ray energy dispersive spectroscopy (EDX) for chemical analysis conduction. The results from the wear experiments indicate that the hybrid material possesses a lower COF, mass wear, and specific wear rate as well as a higher wear resistance in comparison to the B83 babbitt specimen when subjected to the same test conditions. The results from the wear experiments indicate that by applying different loads of 40, 50, and 60 N, the hybrid material possesses a lower mass wear, specific wear rate, and COF specifically at a load of 40 N in comparison to the B83 babbitt specimen under the same test conditions. It was also observed that by increasing the load under dry sliding friction, the hybrid material increases its mass wear and specific wear rate.