# Effect of Designed 3D Reinforcement in Mitigating Machining Damage on CFRP Plates

Thiago Luiz Lara Oliveira, Daniel Brighenti Bortoluzzi, Antônio Carlos Ancelotti

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Thiago Luiz Lara Oliveira, Daniel Brighenti Bortoluzzi, Antônio Carlos Ancelotti. Effect of Designed 3D Reinforcement in Mitigating Machining Damage on CFRP Plates. Polymer Composites, In press, 10.1002/pc.70595 . hal-05489096

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RESEARCH ARTICLE

OPEN ACCESS

# Effect of Designed 3D Reinforcement in Mitigating Machining Damage on CFRP Plates

Thiago Luiz Lara Oliveira<fnref n="1" />,² ID

Daniel Brighenti Bortoluzzi<fnref n="1" />

Antônio Carlos Ancelotti Jr<fnref n="1" /> ID

**Correspondence:** Thiago Luiz Lara Oliveira (tllo@unifei.edu.br)

**Received:** 7 September 2025 | **Revised:** 20 October 2025 | **Accepted:** 20 October 2025

**Funding:** This work was supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico; Fundação de Amparo à Pesquisa do Estado de Minas Gerais.

**Keywords:** CFRP, surface quality | damage | machining | tufting

## ABSTRACT

Composite materials made of carbon fiber-reinforced epoxy (CFRP) are widely used in aerospace fields due to their high strength-to-weight ratio. However, due to low out-of-plane resistance, these materials are often subject to processing damage, such as delamination and matrix cracking, affecting their mechanical properties. The novelty of this paper lies in using a 3D reinforcement to mitigate machining-induced damage on CFRP, specifically evaluating both compressive strength and surface quality. By comparing tufted and non-tufted specimens under various machining conditions, the research demonstrates that tufting achieves up to 14% higher compressive strength and a 36% reduction in surface roughness. These mechanical benefits are obtained without a significant increase in material thickness. These findings highlight tufting as a practical and effective 3D reinforcement technique, providing a valuable framework for integrating advanced reinforcement strategies into manufacturing processes for high-performance composites.

## 1 | Introduction

Composite materials are frequently employed in aeronautical, naval, and automotive industries, owing to the heightened prospects they present for substituting conventional materials [1-3]. The increased use of composite materials in industries for their lightweight and superior mechanical properties leads to a focus on optimizing design manufacturing of materials for aerospace applications. Among the advantages of the use of composite materials in aircraft is fuel efficiency while keeping structural strength [4, 5]. Currently, carbon and glass fiber reinforced polymers make up the majority of aircraft parts due to their mechanical properties, lightweight, and corrosion resistance [6-8]. For instance, Carbon Fiber Reinforced Plastic materials (CFRP) with different matrix types thermoset and thermoplastic resins have been evaluated for their suitability in the back section of a regional aircraft fuselage [9]. The relevance

of the use of composite materials in the aeronautical industry is primarily for cost reduction and fuel consumption without compromising structural strength [10-12]. Composite materials can achieve higher mechanical strength than aeronautical aluminum, another characteristic that makes the use of these materials more significant in aeronautical structures [13].

Machining composite materials is a secondary manufacturing process aimed at shaping components or creating contours for assembly. For aeronautical applications, the most common machining processes include drilling, milling, turning, and grinding, each involving distinct cutting phenomena tailored to meet the structural and design requirements of composite materials [14-18]. Unlike metals, machining composites presents unique challenges, including higher tool wear, limited cooling due to chip shape, minimal use of cutting fluids, and significant surface damage during the process [19-21].

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

© 2025 The Author(s). *Polymer Composites* published by Wiley Periodicals LLC on behalf of Society of Plastics Engineers.

<footnote n="1">¹Institute of Mechanical Engineering, Universidade Federal de Itajubá, UNIFEI, Itajubá, Brazil | ²Institute Clement Ader, Université Paul Sabatier, Toulouse, France</footnote>
## Summary

* 3D reinforcement reduces machining damage at edges and joints prone to failure in CFRP composites.

* Tufted samples show +14% strength and -36% surface roughness.

* Tufting shifts fracture to shear mode, lowering delamination, achieved without increasing thickness significantly.

* Practical strategy to improve durability of composite parts used in structural components.

The phenomenology of the machined surface and material damage for composite materials is influenced by a high number of factors, such as material properties, tool characteristics and machining input parameters, making the entire machining process a complex field of study [22, 23]. Given the high value of products utilized in the aeronautical industry, the machining of these materials is centered on ensuring the quality of the final product, including the prevention of damage [24]. Machining of polymeric composite materials generates fine powder-like chips with low heat dissipation, potentially causing matrix damage due to high temperatures and health risks if inhaled [25, 26].

Machining parameters significantly influence surface finishing and mechanical properties, with improper input parameters resulting in low surface quality and degrading mechanical performance. Research demonstrated that controlling machining temperatures by adjusting cutting speed and feed rate can prevent matrix degradation or facilitate the cutting process, especially by maintaining temperatures near or below the glass transition temperature (Tg) [27, 28]. The damage caused by the machining process is dominated by machining input parameters, including tool geometry. Improper parameters can lead to reduced load-carrying capacity, strength, and stiffness, particularly in glass fiber reinforced polymer (GFRP) composites where damage can detrimentally affect fatigue life and assembly performance [20, 29]. Therefore, careful study and selection of cutting tools and process parameters are necessary to minimize machine-induced defects such as burrs, tearing, delamination, and matrix degradation directly compromising structural integrity, long-term reliability, and fatigue life [30, 31].

Regarding surface finishing, different machining phenomena, such as conventional milling and abrasive water jet (AWJ) milling, can achieve similar surface roughness values with different effects on mechanical properties and defect types [32, 33]. Tool wear is another relevant factor, with higher wear levels causing greater surface damage, increased roughness, and negatively influencing mechanical performance [26, 34, 35]. Additionally, fiber orientation relative to the feed direction and cutting speed influences surface quality, with mismatched angles leading to higher roughness and damage. Proper optimization of machining parameters is thus essential to minimize surface defects and preserve the material's mechanical integrity [36]. Machining processes inherently cause surface damage to composites, making the careful selection of machining parameters essential to minimize defects and material degradation [25, 37].

The integration of through-thickness reinforcement in composite materials is often employed for enhancing resistance to out-of-plane loading and impact forces [38]. There are different techniques of 3D, and their proper design has been shown to significantly improve impact resistance, and mitigate structural damage [39–42]. Among these techniques, tufting—originating from the textile industry—evolved into a commercially viable option to be applied in composite materials [43, 44]. This technique involves inserting additional threads through composite layers using a single needle, providing localized reinforcement with minimal disruption to the material's structure [45, 46].

A study investigating the interaction between drilling and 3D tufting reinforcement in aeronautical composites found that both machining parameters and tufting density significantly influence material performance. Using an open-hole tensile test, the study demonstrated that the choice of drilling tools and tufting density directly affected the material's tensile resistance, showing the significance of proper machining and tufting inputs for structural integrity [47].

There are many studies showing that 3D reinforcement strategies can improve the interlaminar strength, toughness, and load-bearing capabilities of CFRP laminates, especially for post-impact scenarios enhancing material overall performance [48, 49]. Compressive testing is a valuable method for evaluating the benefits of tufting, as it assesses load-bearing capacity, joint toughness, and resistance to delamination [43].

This study innovates the investigation into the impact of specifically designed tufting to mitigate damage induced by machining parameters and to intentionally modify mechanical properties and fracture modes in loading areas. It thoroughly examines the role of 3D reinforcement in carbon fiber and epoxy resin composites, focusing on how the, reinforcement, coupled with different machining conditions, influences the quality of machined surfaces and the overall mechanical attributes of the material. A key objective was to delineate the relationship between machining conditions and the performance of the reinforced material versus its unreinforced counterpart. This research establishes a novel manufacturing guideline that synergically incorporates machining with 3D reinforcement design. Such integration aims to fabricate final components with mechanical properties, exhibiting improved surface finishing, particularly in regions prone to stress concentrations.

## 2 | Materials and Methods

### 2.1 | Plate Manufacturing

The CFRP specimens used in this research were manufactured using a 2D carbon woven fabric and epoxy resin, prepared in two configurations: with and without tufted 3D reinforcement. The carbon fabric was a plain weave (SIGATREX SKDL 8051), consisting of 16 layers arranged in a cross-ply configuration, with the 0° direction aligned with the warp and the 90° direction aligned with the weft. The epoxy resin system used was Ampreg 31 base resin combined with Ampreg A31FAST hardener, both from Gurit, mixed at a mass ratio of 100:26, based on recommendations from previous studies [40, 47, 50]. Two groups of materials were prepared: the reference group (without tufting) and the
tufted samples. The tufting thread was an aramid yarn, Twaron 1680, manufactured by Teijin. The properties of the carbon plain weave fabric and the aramid thread are presented in Table 1.

## 2.2 | 3D Reinforcement

In this study, the tufting procedure involved reinforcing the composite plates in the Z direction by inserting a continuous thread

through the woven carbon layers. A mechanically assisted needle inserted the thread vertically through all layers of dry fabric to the desired preform depth, forming a free loop at the bottom. Friction between the thread and fabric secured the tuft, while an EVA plate and polyamide (PA) film shaped and stabilized the loop. The needle then moved horizontally, creating a square pattern with a tuft spacing of 5 mm. A schematic representation of the process is shown in Figure 1a. Specimens were prepared per ASTM D6641 for compressive testing (Figure 1b).

The through-thickness reinforcement was achieved using a CNC router guided by a G-code algorithm to insert aramid fibers into the CFRP preform, as shown in Figure 2a. A metal frame ensured fiber alignment during the tufting process, while tufting was placed near specimen edges to reinforce machined regions; the final tufting placement can be seen in Figure 2b. Other configurations and materials were evaluated for the 3D reinforcement and the choice was made in respect of previous researches [40, 47, 50].

<table><caption>TABLE 1 | Properties of 3D reinforcements threads.</caption><thead><tr><th>Properties</th><th>Carbon fabric</th><th>Properties</th><th>Aramid</th></tr></thead><tbody><tr><td>Surface Density (g/m²)</td><td>300</td><td>Density (g/cm³)</td><td>1.44</td></tr><tr><td>Fiber Type</td><td>Grafil/Pyrofil TR50S</td><td>Ultimate strength (N)</td><td>350</td></tr><tr><td>Elongation (%)</td><td>2.0</td><td>Elongation (%)</td><td>3.6</td></tr><tr><td>Tex (g/km)</td><td>400</td><td>Tex (g/km)</td><td>168</td></tr><tr><td>\Number of Filaments</td><td>6000</td><td>Number of Filaments</td><td>1000</td></tr></tbody></table>

## 2.3 | Machining Conditions

The investigation focused on the machining parameters for milling the edges of CFRP plates to evaluate the interaction between 3D reinforcement and machining-induced damage. As shown in Figure 3, the composite plates were initially segmented using

<figure><img src="image_3.png" /><figcaption>FIGURE 1 | (a) Schematic representation of the tufting procedure; (b) Compressive samples: Reference (without tufting) and Tufted (reinforced). The yellow line indicates the tuft thread.</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>FIGURE 2 | (a) Tufting process using a CNC-integrated device; (b) Tufted plate prior to resin infusion.</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>**FIGURE 3** | Specimen preparation workflow: The CFRP plate was cut into smaller sections using an AWJ and trimmed at the edges with conventional machining.</figcaption></figure>

<table><caption>**TABLE 2** | Milling parameters used for CFRP plates.</caption><thead><tr><td>Machined condition</td><td>Cutting speed (Vc)</td><td>Feed speed (Vf)</td><td>Cutting length (Lc)</td></tr></thead><tbody><tr><td>1</td><td>150 m/min</td><td>500 m/min</td><td>0 m</td></tr><tr><td>2</td><td>33.9 m/min</td><td>29 m/min</td><td>2 m</td></tr><tr><td>3</td><td>339 m/min</td><td>29 m/min</td><td>4 m</td></tr></tbody></table>

an AWJ to divide them into smaller sections, facilitating preparation for compressive testing. The AWJ process was used to ensure uniform cutting conditions and enable consistent preparation for compressive testing.

Conventional trimming was conducted using a CNC universal machining center (DMG Mori DMU 80 monoBLOCK) with 5-axis capability and a SIEMENS 840D control system. A 6 mm diameter multi-flute cutting tool, coated with Titanium Diboride (TiB2), was used for machining. Process parameters, including feed speed, feed rate, and tool wear, were adjusted to assess their impact on surface finishing and to prepare specimens with the precise dimensions required by the ASTM D6641 standard for compression testing.

To investigate the effects of machining parameters on CFRP plates, three conditions were evaluated to produce varying levels of damage, as shown in Table 2. Condition 1 used high cutting and feed speeds with a new tool to minimize machining damage. Condition 2 employed lower speeds and moderate tool wear to reduce thermal damage. Condition 3 used a high cutting speed, low feed speed, and significant tool wear to generate extensive fiber and resin damage. These conditions facilitated a comparison of machining-induced damage and the performance of the 3D reinforcement. The selected parameters were based on prior studies achieving varied surface finishes [26, 34].

## 2.4 | Surface Quality

The evaluation of the quality of the machined surfaces was performed using a digital microscope and 3D surface profiling

equipment. The Keyence 7000 digital microscope provided high-definition images for visual inspection, with a magnification of up to 6000×. For quantitative roughness measurements, the Alicona Infinite Focus equipment was employed, offering 3D surface profiling of scanned areas, in this case a 5×5 mm square with a topographic range of 2000 µm. This setup enabled both qualitative visualization and quantitative analysis of surface roughness and topography in the examined areas.

## 2.5 | Mechanical Tests

The mechanical tests aimed to evaluate the impact of tufting on CFRP specimens subjected to varying surface finishes and machining-induced damage. Compressive tests were executed for all conditions, with and without tufting, across three machining setups, following ASTM D6641 for quasi-static tests at room temperature. The tests utilized an Instron 8561 servo-hydraulic system with a constant displacement rate of 1 mm/min applied until specimen failure, while load-displacement data were recorded by a 3D Digital Image Correlation (DIC) system. This setup ensured precise characterization of tufting's effects on material fracture behavior.

For each machining condition, a minimum of three specimens was tested to ensure the statistical relevance of the results. Statistical analyses were performed using Minitab software (version 1.110). The analysis workflow included data normalization and outlier detection to verify assumptions of normality and homogeneity of variance. Analysis of Means (ANOM) was employed to identify significant deviations among group means, while Levene's test was used to confirm the equality of variances. Hypothesis testing was conducted at a significance level of *p* < 0.05 to determine statistically significant differences between tufted and non-tufted samples under the various machining conditions.

## 3 | Results

The results of this study examine the fracture patterns, stress-strain relationships, and surface quality of CFRP specimens subjected to varying machining conditions (MC1, MC2,
and MC3) and tufting designs (Reinforced and Reference). Compressive tests were conducted following ASTM D6641, the mechanical properties were correlated with surface roughness parameters (Sa, Sq, Sz), while fracture morphology was analyzed to highlight differences between tufted and non-tufted samples. Statistical analyses emphasized the significance of tufting in improving surface quality and material performance.

Regarding machined surface quality prior to mechanical testing, Figure 4 presents the surface profiles of both reference and reinforced samples under Machined Condition 3. The reference sample exhibits a significantly damaged surface, Figure 4a, marked by machining-induced defects such as fiber pull-out, fiber fracture, and interfacial debonding. These defects appear to be associated with irregularities in the topographic profile, in the form of deeper valleys and abrupt height transitions, suggesting localized fiber removal and uneven material response. The waviness pattern indicates that fiber bundles were inconsistently severed or detached from the matrix, leading to a rougher surface finish and reduced structural cohesion. These phenomena are consistent with the lower mechanical properties observed in the compression tests.

In contrast, the tufted (reinforced) sample, shown in Figure 4b, appears to have a more homogeneous and continuous waviness along the machined surface, indicating reduced machining-induced damage. The surface appears smoother and less disrupted, with damage mostly linked to matrix smearing rather than fiber-related mechanisms. This difference is further supported by the topography, where the reinforced surface maintains shallower relief and fewer abrupt changes in height. In this sense, it was expected that tufting would anchor fibers more effectively through the thickness, reducing the likelihood of pull-out or interfacial failure under machining stresses. This is also reflected in the surface topography, in terms of height subrange color map, where the reference sample shows isolated green-to-yellow peaks, indicating higher surface roughness, while the reinforced sample remains mostly within the blue-to-green range, confirming a smoother surface profile. Nonetheless, while tufting seems to substantially improve surface integrity, it only mitigates the detrimental effects associated with harsh machining conditions.

Figure 5 shows post-compressive fracture images for all studied conditions. The fractures shown for tufted samples appear to be

<figure><img src="image_6.png" /><figcaption>**FIGURE 4** | Comparative analysis of surface finishing for reference and reinforced samples under the same machining conditions. (a) The reference sample exhibits a higher variety and levels of damage, with a rougher surface profile. (b) The tufted sample presents improved fiber cohesion and a smoother surface.</figcaption></figure>
<figure><img src="image_7.png" /><figcaption>**FIGURE 5** | Post-compressive fracture images of CFRP samples under varying machining conditions. The left column presents reinforced (tufted) specimens, while the right column shows reference (unreinforced) specimens. For both groups, fracture severity increases progressively from Machined Condition 1 to Machined Condition, corresponding to increasing surface roughness. The reference samples exhibit extensive delamination and longitudinal cracking, indicating brittle failure dominated by interlaminar separation and matrix fracture. In contrast, reinforced specimens display localized and shear-dominated fractures, with tufting effectively bridging layers and constraining crack propagation.</figcaption></figure>

more localized and less pronounced in delamination compared to the reference samples. In the tufted sample, the fracture is characterized by its localized nature, indicative of the ability of the tuft to hold the crack propagation and maintain the integrity of surrounding areas. This is consistent with the reinforcement behavior of tufting, which acts to bridge the layers of the composite material. The reference samples show a more extensive and diffuse fracture pattern, with more significant levels of delamination, occurring along the layers of the composite. This type of fracture behavior suggests a less effective transfer of stress across the composite layers, leading to a more brittle failure and highlighting the absence of through-thickness reinforcement that tufting provides.

Machining quality also had an impact on fracture behavior, with rougher machining conditions leading to more extensive fractured zones, for both tufted and reference samples. Tufted samples demonstrate a shear-dominated failure, whereas the reference samples exhibit increased delamination with a decrease in machining quality. Reference samples under rougher machining conditions exhibited severe delamination, larger fracture areas, and reduced material integrity, emphasizing the role of tailored tufting in improving damage tolerance. These findings suggest that tufting provides benefits in terms of failure mode and reduces the extension of the machining damage, while it cannot fully compensate for the detrimental effects of harsh input milling parameters.

Figure 6 supports these findings. Under equal machining conditions, the tufted sample exhibits failure along a 45° angle (area

delineated by a yellow line), consistent with a shear-dominated failure mode induced by the reinforcing effect of tufting. In contrast, the reference sample shows evidence of longer buckle delamination (area delineated by a white line), a typical brittle failure mode for CFRP laminates under compressive loads, associated with reduced energy absorption and structural integrity.

Figure 7a shows a through-thickness cut of a specimen near the tufting placement within the composite plate. The tailored tufting design did not significantly increase the composite's overall thickness, which remained approximately 5 mm for both tufted and untufted samples. Measurements indicated minimal resin deposition over the fiber layer, adding only 0.1 mm, consistent across all samples [47].

A water jet texturing procedure was used to validate the negligible thickness increase due to tufting. Operating at 500 bar pressure, 100 mm standoff distance, and 15,000 mm/min traverse speed, the process removed the upper resin layer, resulting in minor fiber exposure and tuft removal on the surface, as shown in Figure 7b. The disrupted fibers and crater formations below 200 µm confirm the minimal resin deposition and support the structural efficiency of the 3D reinforcement design. This optimized tufting approach ensures a high strength-to-weight ratio without compromising the composite's weight efficiency.

Figure 8 shows the stress-strain curves for CFRP specimens under compressive testing, showing the effects of tufting and
<figure><img src="image_8.png" /><figcaption>**FIGURE 6** | Comparative failure modes of CFRP samples subjected to compressive testing under identical machining conditions. The tufted sample (a) exhibits a shear-dominated failure mode along a 45° angle (yellow line), indicating the reinforcing effect of tufting. The reference sample (b) displays longer buckle delamination (white line), typical of brittle failure in CFRP laminates under compressive loads.</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>**FIGURE 7** | Surface analysis of tufted specimens. (a) Through-thickness view showing reinforcement threads and surface resin layer with no significant thickness increase. (b) Surface profile after water jet texturing, highlighting areas with removal depths exceeding 200 µm caused by AWJ. The findings confirm minimal resin deposition and validate the structural efficiency of the tufting design.</figcaption></figure>

machining conditions. For MC1, both tufted and reference samples exhibit similar initial stiffness, as reflected in the similar slopes of the curves at lower strain values. However, the tufted samples achieve higher ultimate compressive strength, likely due to improved interlaminar bonding and fiber alignment provided by the tufting process.

Regarding the MC2, the initial stiffness remains comparable between tufted and reference samples, but tufted specimens consistently demonstrate slightly higher stress values at equivalent strain levels. This indicates enhanced compressive strength and damage tolerance from tufting, particularly at higher strain values where the tufted samples maintain their performance. The reference samples show reduced strength, which may be attributed to increased delamination and surface defects resulting from the machining process (as shown in Figure 6).

For MC3, representing the most severe machining conditions, the stress-strain curves show the significance of tufting in mitigating machining-induced damage. Reference samples exhibit a marked reduction in stiffness and ultimate strength, likely due to extensive delamination and machining defects. In contrast, tufted samples maintain higher strength and demonstrate greater resilience, underscoring the protective role of tufting against poor machining quality.

Statistical analyses supported the qualitative observations, demonstrating the significant effects of machining conditions and tufting on CFRP specimen performance. For ultimate compressive stress, analysis of means (ANOM) indicated that machining quality deterioration from MC1 to MC3 led to reduced stress capacity, while tufted samples consistently exhibited higher stress values than non-tufted samples. Variance
<figure><img src="image_10.png" /><figcaption>**FIGURE 8** | Stress-strain curves for CFRP specimens under varying machining conditions, with and without reinforcement. Reinforced samples exhibit consistently higher strength, particularly under rougher machining conditions (MC3), indicating the effectiveness of tufting in mitigating machining damage and enhancing structural integrity.</figcaption></figure>

tests revealed reduced variability in strain for tufted samples, highlighting their enhanced stability under compressive loading.

Surface roughness analyses (Sa, Sq, Sz) confirmed that machining conditions significantly influenced surface quality, with rougher machining (MC3) producing higher roughness values. Tufted samples displayed consistently lower roughness across all conditions, as supported by ANOM and equal variance tests, which showed statistically significant differences in roughness variability. These findings underscore tufting's role in mitigating machining damage and maintaining surface integrity.

In summary, statistical tests, including ANOM and equal variance analyses, reinforced the conclusion that the reinforcement was able to increase mechanical performance and surface quality, even under varying and harsher machining parameters.

## 4 | Discussion

The results demonstrate a correlation between tufting and improved mechanical performance of CFRP composites, particularly in mitigating machining-induced damage. This section discusses the implications of these findings, focusing on mechanical properties, fracture behavior, and the role of machining parameters in shaping performance.

Under all machining conditions, tufted reinforced samples maintained higher ultimate compressive strength and

exhibited more uniform stress distribution, even at higher strain levels. This indicates that tufting not only enhanced the material's resistance to machining damage but also has improved its overall stiffness and structural integrity. By maintaining a similar thickness to non-tufted samples, tufted composites achieve a superior strength-to-weight ratio, making them highly suitable for high-performance structural applications. Fracture analysis revealed significant differences between tufted and non-tufted samples, especially under severe machining conditions. Tufted samples predominantly exhibited shear-dominated failure modes, with fractures that were more localized and less severe. This contrasts with the extensive delamination and brittle failure modes observed in reference samples, which showed prominent damage propagation. These findings underscore tufting's ability to contain machine-induced damage and improve fracture toughness, thereby enhancing the overall durability and performance of CFRP composites.

Regarding the machining conditions tested, a significant influence on the compressive strength and strain capacity of CFRP samples was observed. Optimized cutting parameters (MC1) resulted in higher strength and strain capacity, emphasizing the importance of surface quality. In contrast, harsher machining conditions (MC2 to MC3) led to reduced mechanical performance due to increased surface damage and defects. This effect was particularly pronounced in reference samples, which were more susceptible to stress and damage propagation under harsh machining conditions.

Comparing Figure 9a,b reveals an inverse relationship between Sa and ultimate compressive strength, with smoother surfaces
<figure><img src="image_11.png" /><figcaption>**FIGURE 9** | Average values for ultimate compressive strength (a) and mean roughness profile (Sa) (b) across machining conditions (MC1, MC2, MC3) and sample types (Reinforced and Reference), with trend lines highlighting the relationship between surface quality and mechanical performance.</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>**FIGURE 10** | Scatter plot showing the relationship between ultimate compressive strength and surface roughness (Sa) across all machining conditions and the presence of 3D reinforcement. Symbols represent machining conditions and tufting presence, with annotations highlighting key trends.</figcaption></figure>

(lower Sa) corresponding to higher compressive stress values. This result also suggests that improved surface quality results in a more uniform and intact material structure, conducive to better mechanical properties. The trend lines in the charts further emphasize this inverse relationship between surface roughness and mechanical performance.

Statistical analyses reinforced the relevance of tailored tufting in mitigating machining damage and enhancing mechanical properties. Figure 10 shows the scatter plot of ultimate compressive strength against Sa for each machining condition, with tufted samples consistently outperforming their non-tufted counterparts at similar Sa values. This confirms that the result aligns with tufting's rising load-bearing capacity of CFRP, regardless

of machining condition. Additionally, compressive strength decreases progressively from Machining Condition 1 to 3, aligning with findings that increased surface damage and roughness diminish mechanical performance [32, 34].

Statistical analyses reinforced the qualitative observations, demonstrating the significant influence of machining conditions and tufting on CFRP specimen performance. For ultimate compressive strength, analysis of means (ANOM) revealed that optimized machining conditions (MC1) resulted in higher strength values, while harsher machining conditions (MC2 and MC3) led to progressively reduced mechanical performance. Tufted samples consistently exhibited higher compressive strength across all machining conditions, highlighting the effectiveness
<figure><img src="image_13.png" /><figcaption>**FIGURE 11** | Conceptual schematic illustrating machining-induced dimensional deviation in tufted and untufted CFRP samples. While both are machined with the same nominal width (W), tufted samples exhibit smoother surface roughness (lower Sz variability), due to effective damage mitigation.</figcaption></figure>

of tufting in mitigating the detrimental effects of machining-induced damage. Variance analyses for strain demonstrated reduced variability in tufted samples, suggesting enhanced stability under compressive loads compared to reference samples.

Surface roughness analyses (Sa, Sq, Sz) further validated the relationship between machining conditions and surface quality, showing that rougher machining conditions (MC3) resulted in higher roughness values. However, tufted samples consistently displayed smoother surfaces across all conditions, as confirmed by ANOM and equal variance tests, which highlighted statistically significant differences in roughness variability. Figure 4 showed qualitatively the comparison between surfaces and allied to these results it emphasizes tufting's significance in maintaining surface integrity and mitigating machining damage. The perspective of dimensional deviation due to machining was addressed in previous studies, highlighting the increase in nominal width (W) as a result of machining-induced damage [51]. In this context, a conceptual representation of this factor is shown in Figure 11, where untufted samples exhibit higher surface roughness (Sz), while tufted samples effectively mitigate the damage, resulting in a smoother surface (lower Sa).

The results underscore the relevance of tailored 3D reinforcement in reducing machining-induced damage while improving surface quality and mechanical properties. By controlling surface roughness and integrating tufting into CFRP structures, material performance is effectively optimized, making tufting design a valuable strategy for applications demanding high strength-to-weight ratios and enhanced durability under diverse machining conditions.

## 5 | Conclusion

The findings of this study highlight the critical role of tufting in reducing machining-induced damage while improving the mechanical performance of CFRP samples. Tufting significantly reduces surface roughness, a key indicator of machining quality, under varied machining conditions. Moreover, the strategic integration of tufting as a 3D reinforcement enhances mechanical properties without a significant increase in plate thickness,

preserving the strength-to-weight ratio essential for advanced composite applications.

Machining quality was shown to directly impact the compressive strength of CFRP samples. Statistical analyses further validated the qualitative findings, demonstrating that tufted samples consistently outperformed non-tufted ones by exhibiting more localized damage, reduced delamination, and improved structural integrity.

The results underscore the importance of tailoring tufting design to mitigate machining damage, preserve surface integrity, and enhance resistance to compressive loads. These insights emphasize the potential of optimized through-thickness reinforcement designs to advance high-performance manufacturing processes for composite materials, particularly in demanding aeronautical applications.

## Author Contributions

**Thiago Luiz Lara Oliveira:** conceptualization, data curation, formal analysis, visualization, writing – original draft, methodology, investigation, writing – review and editing, software, validation. **Daniel Brighenti Bortoluzzi:** conceptualization, investigation, methodology, formal analysis. **Antônio Carlos Ancelotti Jr:** project administration, supervision, funding acquisition, resources.

## Acknowledgments

The authors gratefully acknowledge the financial support provided by the National Council for Scientific and Technological Development (CNPq) under CNPq call 26/2021, project number 200884/2022-0/PDE. This research was also supported by the Minas Gerais State Research Foundation (FAPEMIG) under project APQ01846-18. The authors would like to thank Laurent Crouzeix, Nathalie Rocher Gleizes, and Redouane Zitoune from Institut Clément Ader for their valuable assistance, as well as Zoheir Aboura from Université de Technologie de Compiègne for his support during this study. The Article Processing Charge for the publication of this research was funded by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) (ROR identifier: 00x0ma614).

## Conflicts of Interest

The authors declare no conflicts of interest.

## Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

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