Experimental Investigation Concerning the Influence of Face Sheet Thickness on the Blast Resistance of Aluminum Foam Sandwich Structures Subjected to Localized Impulsive Loading

Abstract

This study presents an experimental investigation into the dynamic response and blast resistance of aluminum foam-cored sandwich panels with varied face sheet thicknesses under impulsive loading conditions. The primary focus is on analyzing how the thickness of front and back face sheets affects the deformation behavior and energy absorption capabilities of the sandwich panels. By employing a 3D digital image correlation (3D-DIC) system coupled with post-test analyses, the dynamic responses and permanent deformations were quantitatively characterized. Failure modes of the core layers, front face sheets, and back face sheets were identified and discussed. The results demonstrated that sandwich panels with thick front face sheets exhibited superior blast resistance and energy absorption performance than their thin-front counterparts under high localized impulsive loading. The findings provide important comparative insights about face sheet thickness distribution effects, though further studies with broader thickness variations are needed to establish comprehensive design guidelines.

1. Introduction

Under impulsive loading conditions, structures experience transient, high-intensity stress waves, where dynamic response, failure mechanisms, and energy absorption play critical roles in blast resistance. Blast resistance refers to the ability of a material or structure to withstand and mitigate the effects of explosive or impulsive loading. It is a critical performance metric in aerospace, military, and civil engineering applications, where structures are exposed to dynamic loads—such as blast shields in defense facilities, rein-forced buildings in urban security zones, and aircraft components subjected to shock waves. The design of blast-resistant systems often involves optimizing material properties and structural configurations to dissipate kinetic energy and minimize catastrophic failure.

Owing to their exceptional stiffness-to-mass ratio, sandwich structures have been widely implemented in commercial and military vehicle designs as alternatives to solid monolithic counterparts. As a structural-functional material with high porosity, aluminum foam maintains constant nominal stress during large plastic deformation. When subjected to static or dynamic loads, the aluminum foam core in lightweight sandwich panels enables substantial energy absorption through pronounced plastic deformation [1].

The energy dissipation capacity of sandwich structures during impact events is directly correlated with their deformation patterns and failure progression. Sandwich panels generally consist of a low-density core with face sheets on both sides. Nurick and Shave [2] experimentally investigated the impulsive loading of square metallic plates and identified three primary failure mechanisms: extensive ductile deformation, tensile tearing, and transverse shear. Xu et al. [3] proposed three improved dimensionless numbers that outperform Nurick’s model in prediction accuracy, and developed a general approach for constructing simplified mode solutions for final plastic deformation of circular plates under localized impulsive loading. Nagesh and Gupta [4] employed three failure criteria to predict the structural response of clamped circular steel plates under uniform impulsive loads. The results demonstrated a satisfactory correlation with experimental data in large permanent deformations and tensile rupture/fracture.

Low-density foams exhibit extensive civil and military applications, particularly as core materials in sandwich structures. Zhou et al. [5] experimentally characterized the uniaxial and biaxial failure mechanisms in aluminum alloy foams, revealing distinct deformation patterns under different loading conditions. Radford et al. [6] showed that aluminum foam-core sandwich structures outperform monolithic plates in shock resistance. The primary research objective focuses on engineering lightweight structures with optimal stiffness-to-weight ratios coupled with exceptional energy absorption capacity. Yuan et al. [7] systematically evaluated polymer-foam composites, demonstrating enhanced mechanical performance through failure mode analysis and compressive property evaluation, particularly in energy dissipation and stress stabilization. Impulse loading experiments have provided critical insights into deformation processes and damage evolution in composite structures [8,9,10]. Fleck et al. [11] developed analytical models for blast-resistant behavior characterization of metal sandwich beams in both air and underwater environments, establishing fundamental design principles. Qiu et al. [12] established a theoretical framework to predict the nonlinear deformation of clamped circular sandwich structures under impulsive loading. Zhu et al. [13] combined experimental and analytical approaches to evaluate the blast resistance of square metallic sandwich panels with honeycomb and aluminum foam cores, subsequently developing a mass-constrained optimization strategy for the composite structure. Ren et al. [14] investigated the impact resistance of composite foam-core sandwich plates through high-velocity projectile tests, revealing that high density significantly enhances impact resistance while maintaining areal mass, with high-density cores demonstrating superior energy absorption efficiency. Huang et al. [15] systematically characterized the dynamic failure mechanisms of sandwich structures with symmetric face sheets under impact loading conditions. Through coupled experimental-FEM approaches, Xu et al. [16] and Mao et al. [17] systematically analyzed the blast-resistant performance of aluminum foam-cored sandwich panels, demonstrating strong agreement between simulation and empirical data. Arumugam et al. [18] indicated that less stiff structures undergo significant deformation, which reduces the load acting on the structure compared to more-stiff structures.

Radford et al. [19] pioneered a novel laboratory technique employing metallic foam projectiles to replicate both aquatic and aerial blast profiles on structural elements. Their approach demonstrated the capability to generate characteristic pressure–time curves reliably while maintaining operational simplicity and safety. Adopting this experimental methodology, Ye et al. [20], Deng et al. [21], and Mei [22] employed aluminum foam projectile impact to investigate the dynamic response of sandwich structures under localized impulsive loading conditions. Yu et al. [23] utilized composite projectile impact to simulate sequential fragment impact and blast loading generated by cased charge explosions. Despite the three-layer configuration, research on sandwich panels primarily focuses on the core layer, which includes aluminum foam core [8], PVC foam core [14], tetrahedral truss core [15], S-shape fold core [20], star-shaped reentrant core [24], hemispherical-shell core [25], density-graded cellular core [26], and auxetic honeycomb core [27,28]. The other two face sheets are frequently investigated simultaneously, typically constructed from identical materials and possessing uniform thickness. Jamil et al. [29] studied blast-resistant sandwich panels with identical face sheets, observing that tearing failure modes (partial and tensile) exclusively manifested in the back face sheet. Zarei and Sadighi [30] investigated the effect of face sheet thickness on energy absorption characteristics, demonstrating that thicker symmetric face sheets diminish specific energy absorption capacity by suppressing failure modes such as wrinkling. Mei [22] demonstrated that sandwich panels with low core density and thick face sheets achieve superior impact resistance while maintaining equal mass in most experimental cases.

Significant disparities exist in both failure modes and mechanisms between the front and back face sheets of sandwich panels, necessitating distinct evaluation of their respective thickness effects on blast resistance performance. This study aims to examine how varying the thickness of sandwich panel face sheets (both front and back) influences structural response under impulsive loading conditions. Utilizing 3D-DIC methodology, this study experimentally characterizes the dynamic deformation fields, failure mechanisms, and blast-resistant performance of aluminum foam-cored sandwich panels under impulsive loading conditions.

2. Material Properties

The sandwich panels consist of 5A06 aluminum alloy face sheets and closed-cell aluminum foam cores, with their mechanical properties listed in

Table 1. Mechanical properties of 5A06 aluminum alloy and aluminum foam.

Material	Density (Kg/m3)	Young’s Modulus (MPa)	Poisson’s Ratio
5A06 aluminum alloy	2780	74,000	0.32
aluminum foam	300	80	0.10

.

2.1. Aluminum Foam

For both dynamic and quasi-static compression tests, Φ30 × 10 mm specimens were machined from a single 10 mm-thick aluminum foam plate. Quasi-static and dynamic compression tests were conducted on the compressible solid foam specimens to characterize their stress–strain behavior across different strain rates. The quasi-static tests employed an electronic universal testing machine, while dynamic tests utilized a Φ40 aluminum split Hopkinson pressure bar.

The stress–strain response of aluminum foam exhibits three characteristic regimes: (1) Elastic deformation with near-linear stress–strain correlation, (2) Plateau stage maintaining relatively constant stress over extended strain, and (3) Densification involving exponential stress rise after cellular structure collapse. Zhao et al. [31] systematically reviewed the constitutive law testing methods for metallic cellular materials, along with their strain-rate sensitivity mechanisms. As shown in Figure 1, both quasi-static and dynamic tests demonstrated excellent repeatability, revealing significant shock enhancement effects where the dynamic plateau stress exceeded its quasi-static counterpart by 97%.

Lightweight foams demonstrate exceptional energy absorption capacity due to their characteristic plateau stress behavior, where progressive cell structure collapse occurs until densification initiates. A method to identify the energy absorption and optimum usage characteristic of foam material is called the energy efficiency parameter. The energy absorption efficiency η is mathematically expressed as follows [32]:

$$\eta ={\displaystyle \frac{{\displaystyle {\int }_0^{\epsilon }\sigma (\epsilon )\mathrm{d}\epsilon }}{\sigma (\epsilon )}}$$

(1)

where σ and ε represent stress and strain of the foam material, respectively. Figure 2 presents comparative efficiency-strain and stress–strain responses of aluminum foams under both static and dynamic loading conditions. It is found that the maximum dynamic and static efficiencies are very close, which are 0.24 and 0.26, with the densification strain of 0.41 and 0.44. While the densification stresses are 3.86 MPa in dynamic loading, and 1.81 MPa in static loading.

2.2. 5A06 Aluminum Alloy

The sandwich panels in this study utilize 5A06 aluminum alloy for face sheets. The mechanical behavior of 5A06 aluminum alloy is characterized using the Johnson–Cook constitutive model, which incorporates strain hardening, strain rate sensitivity, and thermal softening effects. The constitutive model parameters are listed in

Table 2. Johnson-Cook constitutive model parameters of 5A06 aluminum alloy [15].

Material	A (MPa)	B (MPa)	N	C	m
5A06 aluminum alloy	167.0	443.7	0.44	0.02	2.3

.

3. Experimental Setup

3.1. Sandwich Configurations

The sandwich panels fabricated with dissimilar-thickness aluminum alloy face sheets, separated by the closed cell aluminum foam layer. For comparison purposes, two distinct sandwich panel configurations were investigated. As detailed in

Table 3. Two sandwich panel configurations (Unit: mm, thickness of the core layer: 10 mm).

Configuration	Thickness of Front Sheet	Thickness of Back Sheet
1	0.5	1.0
2	1.0	0.5

, configuration 1 features a 0.5 mm front face sheet and 1.0 mm back face sheet, while configuration 2 features a thick front sheet (1.0 mm) and a thin back sheet (0.5 mm). The core layers of both configurations are identical, each 10.0 mm thick with a density of 0.30 g/cm³. Both configurations share identical core layers but exhibit reversed face sheet thickness arrangements (front/back), with their masses, thicknesses, and areal densities remaining equivalent.

3.2. Test Configurations

A lab-scale impulsive loading system was developed using a Φ40 mm single-stage light gas gun to propel projectiles. Cylindrical aluminum foam projectiles (Φ40 × 30 mm, 0.35 g/cm³ density) were employed to simulate shock loading [19]. Figure 3 illustrates the customized experimental apparatus utilized in these tests. The projectile’s impact velocity was recorded using a vertically oriented Phantom high-speed camera (Vision Research Inc., Wayne, NJ, USA).

The tests utilized Aramis, an optical 3D deformation analysis system characterized by its non-contact and material-independent measurement capabilities. As shown in Figure 3, a paired setup of high-speed cameras captured the panels’ dynamic deformations, enabling three-dimensional digital image correlation (3D-DIC) analysis through synchronized image processing. At a frame rate of 36,000 fps, the high-speed cameras captured the sandwich panel’s dynamic response characteristics.

Figure 4 illustrates the support configuration and composition of the analyzed sandwich panels. The sandwich specimens were rigidly clamped between two thick armored steel plates using eight high-strength bolts distributed along a 160 mm pitch circle diameter. This clamping configuration creates essentially fixed boundary conditions around the entire perimeter of the specimen, effectively preventing both translational and rotational displacements at the edges. Post-test examination showed no measurable slippage or rotation at the clamped edges.

4. Results and Discussion

This study focuses on characterizing the dynamic response and blast resistance performance of foam-cored aluminum sandwich panels under impulsive loads. Two panel configurations were tested using a gas gun setup to evaluate their blast resistance. Quantitative analysis was performed by introducing a dimensionless parameter, the normalized impulse, defined as [14]:

$$I^{*}={\displaystyle \frac{I}{Ah\sqrt{\rho {\sigma }_{ys}}}}$$

(2)

where A, h, ρ, and σ_ys denote the cross-sectional area, thickness, density, and yield stress of the aluminum foam projectile, respectively, while I represents the total impulse (equivalent to the projectile’s kinetic energy).

Table 4. Experimental results for sandwich panels.

Label	Impact Velocity (m/s)	Normalized Impulse	Failure Mode of Front Face Sheet	Residual Thickness of the Core (mm)	Deformation (mm)	Energy Absorption (J/mm)
1-1	85.8	0.99	I	5.0	5.92	9.09
1-2	122.3	1.42	I	3.2	9.18	11.98
1-3	155.5	1.84	I	2.2	12.58	14.33
1-4	168.2	1.97	I	1.8	14.17	14.78
1-5	213.5	2.40	I	1.5	18.38	17.61
1-6	257.5	2.92	III	1.2	25.00	18.96
1-7	268.2	3.00	III	Shear	26.06	19.46
1-8	263.8	3.11	III	Shear	28.54	18.25
1-9	276.7	3.18	III	Shear	29.58	18.77
1-10	300.9	3.46	III	Shear	33.27	19.73
2-1	72.8	0.84	I	6.1	5.66	6.79
2-2	109.2	1.26	I	4.4	8.33	10.38
2-3	139.5	1.58	I	2.8	10.65	13.07
2-4	190.3	2.16	I	1.9	15.94	16.24
2-5	228.9	2.58	I	1.5	19.90	18.69
2-6	246.9	2.76	I	1.5	21.48	20.01
2-7	272.9	3.11	I	1.4	23.95	22.39
2-8	298.0	3.42	I	1.3	26.57	24.23

summarizes the experimental results of sandwich panels under impulsive loading, including: impact velocities of the aluminum foam projectiles (Φ40 × 30 mm, 0.35 g/cm³), normalized impulses, front face sheet failure modes (mode I: ductile deformation, mode III: shear and tearing), core layer residual thicknesses, panel permanent transverse deflections, and energy absorption efficiency.

4.1. Dynamic Response of Sandwich Panels

Using 3D-DIC, the real-time deformation fields of sandwich panels were quantified at high frame rates. Figure 5 illustrates the deformation evolution of the back face sheet in sandwich panels (tests 1–6) under a normalized impulse of 2.92. The deformation process exhibited pronounced nonlinear characteristics, particularly during the plastic hinge formation and propagation phases. As demonstrated, the sandwich panel under impulsive loading displayed four distinct phases of dynamic deformation:

Phase 1 (0–0.056 ms): The impulse propagates through the core to the back sheet, inducing the formation of a plastic hinge at the center of the back sheet.

Phase 2 (0.056–0.444 ms): Unlike underwater impulsive loading [15], the plastic hinge expands radially toward the fixed boundary, exhibiting circular expansion while central deflection increases monotonically.

Phase 3 (0.444–0.583 ms): Upon reaching the fixed boundary, the plastic hinge stabilizes, and the sandwich panel achieves its maximum central deflection (25.82 mm) under sustained loading.

Phase 4 (>0.583 ms): The target undergoes elastic oscillation within a finite deflection range until complete kinetic energy dissipation.

Figure 6 presents the time-history curves of transverse deflection and radial strain measured by three gauges in Tests 2–6 using digital image correlation. In Figure 6a, three virtual gauges from 3D-DIC (spaced 25 mm apart) reveal initial deformation concentration at the panel center, with propagation delays with radial distance. The back face sheet exhibits rapid transverse deflection growth until peak values (21.56 mm, 16.89 mm, 11.15 mm at respective measurement points), followed by spring-back stabilization. This confirms that permanent deformation decreases with increasing radial distance from the center. Figure 6b reveals three radial strain profiles characterized by rapid initial growth followed by stabilization, with plateau values negatively correlated to radial position. The sustained positive in-plane radial strain throughout deformation confirms radial tensile stress as the dominant failure mechanism for sandwich panel back face sheets. Peak strain localization at the back face sheet center implies that tension induced tearing would likely become the predominant failure mechanism under impulsive loading conditions exceeding the current experimental intensity threshold.

Figure 7 presents the temporal evolution of mid-span deformation for four sandwich panel specimens under impulsive loading. Tests 1–4 and 1–9 belong to configuration 1, while tests 2–4 and 2–6 belong to configuration 2. The curves in Figure 7 show that all specimens exhibited statistically indistinguishable initial deformation rates within the first 0.11 ms, attributable to standardized impact conditions and shared core layer properties. After 0.11 ms, the transverse deformation rate increases with higher impulsive intensity. Comparisons between tests 1–4 (configuration 1: 0.5 mm front sheet) and tests 2–4 (configuration 2: 1.0 mm front sheet) reveal that configuration 1 consistently exhibits higher transverse deformation rates under similar impulse intensities.

The deflection rise time of each structure increases with higher impulsive intensity, as shown in Figure 7, attributable to enhanced material damage accumulation. According to tests 1–4 and tests 2–4, configuration 1 exhibits consistently shorter deflection rise time compared to configuration 2 under similar impulse intensity. After reaching peak transverse deflection, slight spring-back recovery occurs, with no further significant vibrations observed.

As impulsive intensity increases, both the deflection rise time and the deformation rate increase. However, a thicker front sheet (configuration 2) can extend the rise time and reduce the deformation rate, thereby mitigating more critical structural failure modes.

4.2. Failure Modes and Associated Mechanisms of Sandwich Panels

Impulsive loading can cause significant damage to sandwich panels, though their failure modes and severity remain challenging to predict. Understanding these failure modes is critical for structural design, particularly for configurations with high energy absorption capacity, which enhances blast resistance in both sandwich and monolithic structures.

4.2.1. Failure Modes of Front and Back Face Sheets

The sandwich panels in this study feature thin aluminum alloy face sheets on both sides, differing only in their inverted thicknesses. At low applied impulse, only slight inelastic deformation is observed on the two sheets of the sandwich. Global deformations increase with rising impulses, while the core layers continue to compress, and permanent deformations accumulate as the impulse increases, as shown in Figure 8a,b.

As shown in Figure 7, a thicker front sheet can extend the rise time, and reduce the deformation rate, thereby mitigating more critical structural failure modes. When the normalized impulse reaches 2.92, cracks form in the front sheet of configuration 1. According to literature [2], the failure sequence of thin sheets progresses from energy-absorbing ductile deformation to mixed-mode tensile-tearing, ultimately reaching shear failure. However, this study does not observe tensile-tearing failure. The absence of tensile-tearing (mode II) is attributed to the constrained deformation imposed by the 10 mm thick aluminum foam core layer. The foam core’s cellular structure provides continuous lateral support to the front face sheet, effectively suppressing tensile membrane stresses that would otherwise lead to tensile failure. This aligns with the foam’s plateau stress behavior, which stabilizes plastic deformation. The failure modes transferred from large ductile deformation (I) into shear failure directly. Due to the irregular cellular wall structure of the aluminum foam projectile, shear failure induces tearing, leading to a mixed failure mode of shear and tearing (III), as shown in Figure 8c.

When the normalized impulse increases to 3.00, both the front sheet and the core layer of configuration 1 failed in shear mode, and the material discontinuity significantly hindered energy dissipation. In contrast, configuration 2 with thicker front sheets consistently exhibits ductile deformation across all impulse ranges, as shown in Figure 8e.

Figure 8d,f shows the sectional profile for back face sheets of tests 1–7 with permanent deformation of 26.06 mm under normalized impulse 3.00, and tests 2–6 with permanent deformation of 21.48 mm under normalized impulse 2.76. The sandwich panels’ high energy absorption capacity resulted in consistent failure modes of both configurations: all back face sheets exhibited large ductile deformation throughout the tested impulse range, as demonstrated by the inelastic deformation patterns in Figure 9.

Figure 9 illustrates the typical deformation profiles of sandwich panel back face sheets under impulsive loading. At low intensity, the profile approximates a triangular shape with a central circular arc, whereas high-intensity impulses (e.g., Tests 1–9) induce additional central bulging deformation.

4.2.2. Failure Modes and Residual Thicknesses of the Core Layer

Aluminum foam’s suitability as a core material for these applications primarily stems from its exceptional energy absorption capacity, which effectively mitigates permanent panel deformation. Understanding the failure mechanism provides critical insights for enhancing the panel’s blast resistance performance. Under impulsive loading conditions, aluminum foam core failure in sandwich structures primarily results from three mechanisms: cellular structure collapse, compression, shear failure of base material and their synergistic interactions.

As shown in Figure 10, at low impulse intensities, the core layers predominantly exhibited compressive failure. The shapes of the front and back sides of the two core layers are repainted in red in Figure 10a,b. The results indicate that the residual thickness of the core layer in tests 2–4 expands more uniformly along the radial direction, while rapid expansion occurs near the impact boundary of tests 1–4. These findings demonstrate that increasing the front face sheet thickness enhances a sandwich panel’s impulse diffusion capability.

As shown in Figure 10c, sandwich panels with thin front face sheets primarily fail through transverse shear under high impulse loading. This failure mode results from coupled compression-shear interaction, causing complete compression of the sheared region while inducing global deformation in the remaining core layer. In contrast, sandwich panels with thick front face sheets primarily experience compression failure under high impulsive loading.

Energy absorption in sandwich panels is primarily governed by core compression. The residual thicknesses in the mid-span of core layers (initial thickness: 10 mm) were measured in the post test, as shown in Figure 11. The residual thicknesses exhibit a linear decline with increasing normalized impulse up to 2.2 across both configurations. Linear fitting reveals that sandwich panels with thicker front face sheets consistently demonstrate lower residual thicknesses than those with thin front face sheets within this impulsive loading range. Both configurations maintain nearly constant residual thicknesses with further increasing impulse, as their core layers enter the densification region.

When the normalized impulse exceeds 3.00, transverse shear occurs in configuration 1, while configuration 2 shows no transverse shear within the tested impulse range. Table 4 indicates that transverse shear failure develops simultaneously in both the core layer and front face sheet, directly influencing the aluminum foam’s energy absorption performance.

4.3. Permanent Deformation of Sandwich Panels

Permanent deformations of sandwich panels were measured using both a digital micrometer system and 3D-DIC analysis, with the results showing strong correlation (deviation < 5%). The main parameter representing the damage degree is the normalized transverse deformation of the panel, where lower normalized deformation values indicate superior blast resistance. This parameter is defined as [22]:

$$\overline{w}={\displaystyle \frac{D_b}{r}}$$

(3)

where D_b is the permanent transverse deformation of the middle span and r is the back sheet’s radius.

Figure 12 compares the normalized deformation responses of both configurations under impulsive loading. Within the tested impulse range, configuration 1 exhibits a steeper mean slope than configuration 2, indicating that sandwich panels with thin front face sheets undergo accelerated permanent deformation growth with increasing impulse. Conversely, thin front face sheets (configuration 1) demonstrate superior performance under low-impulse conditions, though the performance advantage remains statistically insignificant.

The two curves intersect at a normalized impulse of 1.78, beyond which normalized deflections of configuration 1 exceed those of configuration 2, with the gap widening as impulse increases. For example, at a normalized impulse of 3.44 ± 0.02 (Tests 1–10 and 2–8), configuration 2 outperforms configuration 1 by 20% in permanent deformation, confirming that thick front face sheets (configuration 2) provide superior performance under high-impulse loading.

4.4. Energy Absorption Evaluation of the Sandwich Panels

Sandwich panels with low-density aluminum foam are primarily applied to absorb energy under impulsive loading. Zhang et al. [33] investigated aluminum matrix syntactic foams under impulsive loading, reporting that both cell size and impulse intensity critically govern energy dissipation behavior of the foams. While interfacial friction may dissipate a fraction of the initial kinetic energy, the aluminum foam projectile exhibits no significant upsetting. Its cellular structure inherently limits solid contact area, thereby rendering plastic deformation the dominant energy absorption mechanism.

Experimental results demonstrate that configuration 1 exhibits superior performance under low-intensity impulsive loading, whereas configuration 2 performs better at higher impulse levels. To quantify energy absorption efficiency, a normalized parameter E_d (energy per unit central deformation) is introduced as Equation (4) [34], where higher values indicate better energy dissipation efficiency.

$$E_d={\displaystyle \frac{E_k}{D_b}}$$

(4)

The foam projectile’s initial kinetic energy (E_k) and the panel’s permanent central deformation (D_b) serve as key parameters in this analysis. As shown in Figure 13, similar trends in energy absorption performance for the two configurations are observed until the normalized impulse rises to 2.76, and then the uptrend in energy absorption performance for configuration 2 is continued, while configuration 1 stabilizes at approximately 19 within the tested range.

Comparing the peak energy absorption performance values of the two configurations under impulse loading, configuration 2 outperforms configuration 1 by 24.5%. The thicker front face sheet delays the initiation of core shear failure, thereby extending the stable compression stage and enhancing energy dissipation.

It should be noted that this study only examined two specific face sheet thickness configurations. While the comparison between these configurations revealed important insights about thickness distribution effects, future research should investigate a broader range of thickness combinations to verify the generalizability of these findings.

5. Conclusions

Through systematic gas gun experiments (70–300 m/s) coupled with 3D-DIC analysis, this study deciphers the thickness-dependent dynamic response of aluminum foam sandwich panels under impulsive loading, revealing four deformation phases with characteristic time scales. The experiments also characterize the mechanical properties of the aluminum foam materials. This work systematically examines how face sheet thickness influences the dynamic response of sandwich panels under impulsive loading. Through comparative testing of two configurations, dynamic responses, failure mechanisms, and energy dissipation behaviors are comprehensively analyzed.

The dynamic response of sandwich panels under impulsive loading is quantified using 3D-DIC analyses. Radial strain and transverse deflection of the panels decrease with increasing radial distance from the center. Both the deflection rise time and the deformation rate increase with increasing impulse magnitude. Sandwich panels with a thicker front sheet (configuration 2) can extend the rise time and reduce the deformation rate.

The failure mechanisms are analyzed through a layer-by-layer examination of the sandwich panel structure. The aluminum face sheets predominantly fail through large ductile deformation, with transverse shear and tearing specifically localized in the 0.5 mm thin front face sheet. Tensile-tearing mode remains absent under these operational conditions. The foam core layer primarily exhibits compression failure and transverse shear in these tests. Notably, core-layer transverse shear only manifests when the front face sheet simultaneously fails via transverse shear. Sandwich panels with thick front face sheets demonstrate dual effectiveness: efficiently diffusing impulse while maintaining structural integrity under impulsive loading.

For a given configuration, permanent deflection exhibits monotonic growth proportional to the applied impulse. Experimental results indicate that thin front face sheet sandwich panels demonstrate marginally improved blast resistance under low impulse intensity conditions, though the performance advantage remains statistically insignificant. Thick front face sheet sandwiches show performance advantages under high-intensity loading, outperforming thin ones by 20% in permanent deformation and 24.5% in energy dissipation efficiency. This confirms that thick front face sheets provide superior performance under high-impulse loading, attributable to delayed shear failure of the front sheet and the core layer initiation.

Future investigations should explore a broader range of thickness ratios to identify optimal configurations for specific impulse ranges, based on the fundamental mechanisms elucidated in this study. The insights gained here provide preliminary guidelines for the design of sandwich panels in blast resistance applications, while highlighting the need for more comprehensive thickness variation studies.