Sandwich constructions are widely used in numerous sectors such as aerospace, marine, architectural, and transportation industry acknowledging their excellent light-weight, exceptional corrosion characteristics, and rapid installation capabilities. The combination of the face-sheet and core should be profound so the sandwich structure’s functionality is maintained over its life-span and guarantee structural integrity. The interfacial adhesion between the core and face-sheets plays a vital role to ensure structural integrity. The adhesion is primarily responsible for load transfer between the face-sheets and core and its failure results in severe degradation of the sandwich structure’s functionality. Therefore, this study investigates the significance of adhesive layer application at the skin-core interface while manufacturing Carbon Fiber Reinforced Plastic/End-Grain Balsawood sandwich composites and its impact on the composite’s mechanical performance. Interface adhesive application demonstrated overall improved mechanical behavior under quasi-static flexural loading; which essentially accounts for superior interfacial skin-core bonding. The technique enhances structural performance without a considerable density variant. Numerical results agreed well with the experimental findings and aided in further understanding of the associated damage mechanisms. Sandwich composite’s flexural damage mechanisms were essentially the same irrespective of the presence of reinforced interfacial bond; however; the improved interfacial bond resulted in higher load capacity and reduced skin-core debonding.

A satisfactory reproduction of three-point bending and impact test data of an industrially important amorphous polymer, acrylonitrile-butadiene-styrene (ABS), in the context of finite element analysis is of prime importance to industry. Constitutive material models developed for amorphous polymers are capable of describing their complex mechanical behavior under multiaxial loadings with a variety of success; therefore, the computational accuracy directly depends on the selection of constitutive model and a proper determination of its associated parameters. Thus, this study aimed at accurately predicting the multiaxial mechanical behavior of ABS by the Anand–Gurtin elastic–viscoplastic material model selected as the constitutive model and employed for the first time in the numerical implementations of the three-point bending and impact tests of ABS. To this end, the constitutive model parameters never identified for ABS before was first determined mainly depending on uniaxial compression test data at various strain rates ranging from 2 × 10−4 s−1 to 2 × 10−1 s−1 and then validated against tension test data for a broad range of strain rates varying from 1 × 10−3 s−1 to 45 s−1. All the experimental data taken into consideration in this study was taken from the previous studies of authors. The material model with the validated constitutive parameters of ABS was utilized in the numerical implementation of three-point bending tests for two different bending speeds (0.05–10 mm/s), in addition, impact tests for two various low impact velocities (4.43–6.23 m/s). Numerical results revealed that the constitutive model successfully reproduces the three-point bending test data of ABS for both bending speeds but acceptably overestimates the impact response of ABS under both low impact velocities in terms of peak impact load. Hence, it was concluded that this computationally inexpensive complex material model with the constitutive parameters determined for ABS can be used in the accurate prediction of its multiaxial material behavior.

Under flexural loading, premature indentation of face sheet is a major concern in sandwich-structured composites with a softer core. A composite material having sandwich structure is a special class of composite materials that is developed by adhesively bonding two thin but stiff skins to a lightweight but thick core. ASTM C393 standard recommends the use of a wider load pad under the loading pin to ensure distribution of concentrated load [ 21 ]. However, it does not address how padding influences the overall flexural behavior of sandwich composites. This investigation focuses on evaluating the effect of padding by comparing flexural tests of sandwich beams with and without padding. Rubber and Teflon materials are used as padding, which are adhesively bonded in the sandwich composite beams. Results show that flexural stiffness and peak load carried by the beams are not affected, but the failure modes can change significantly due to load-point padding. More significant core collapse (failure) in the padded case is the key difference in failure modes between the padded and unpadded cases. This change in failure mode requires careful attention, particularly, for the development of a proper test standard. We conducted finite element analysis, which clarifies the stress distribution in the face sheets and in the core due to padding as well as when padding is absent. Finite element analysis results show that greater volume of the core material is subjected to higher level of von Mises stresses, which occurs in the padded case, increasing the probability of core failure. High shear zones are also observed in the case of padding, and balsawood core cracking is consistent with these high shear zones. Results from this investigation shed light on current experimental methods and consequence of padding in altering failure modes and eventual load-deflection response in sandwich composites subjected to flexural loading.

Acrylonitrile–butadiene–styrene (ABS) is a very significant and widely used amorphous thermoplastic which, on account of its importance in industry, multiplied billions of dollars are spent yearly in the United States alone, not to talk of the rest of the world. It is primarily utilized in industry and domestic situations due to its high damage resistance properties. This fact makes it a required exercise for serious and thorough research in this area to go ahead. In this article, the tension, compression, and bending response behavior of ABS material under various strain rate levels tests were investigated. Its characterization under tensile, compression, and other mechanical testing is thus quite important, to elicit ways of enhancing properties that would make the material or structures made from it, better in service. In the current phase, tension, compression, shear, and flexural samples were tested, because it is of interest to know how the longitudinal and shear loading damages propagate through the specimen length and thickness, and how the microstructure is affected from point to point, both laterally and depth-wise. The issues of energy transfer and dissipation are significant in terms of the effectiveness of this material as a damage retarder. Mat_187 nonlinear material model in Ls-Dyna was utilized to numerically evaluate the behavior of ABS under tension, compression, and three-point bending. The experimental results compared favorably to the numerical results.

In the present investigation, we present, the flexural characteristics of carbon fiber reinforced polymer/polyurethane foam and glass fiber reinforced polymer/polyurethane foam sandwich beams having partial debonding between facesheet and core that acts interfacial degradation and hinders the load transfer between facesheets and core. An initial pre-crack between core and face sheet is created by placing a Teflon sheet at the interface on one end of the beams during the manufacturing of sandwich beams. A comparative analysis is carried out to study the effect of using CFRP and Eglass prepregs as face sheet material on such sandwich beams. The flexural behavior of GFRP/PU sandwich beams having initial debond is characterized and analyzed under both three- and four-point loadings. Lastly, the effect of varying the support span length on the flexural response of CFRP/PU sandwich beam having initial debond is also investigated. It was found that the degraded sandwich beams having woven CFRP facesheets have slightly higher stiffness and peak load level as compared to the sandwich beam having cross ply GFRP facesheets. GFRP/PU foam sandwich beam showed higher ductile behavior prior to progressive failure of the sandwich beam. It was observed that the crack tip of the implanted interfacial debond acts as a medium to trigger the interfacial damage followed by the shear failure of the core due to the progression of the initial crack into the core.

Light-weight sandwich composites can be tailored to satisfy many specific application requirements and are inevitable for modern structures where reduced weight is extremely critical. However, these structures are highly vulnerable to debonding at the skin-core interface. The skin-core adhesion is an extremely crucial part of a sandwich structure; mostly responsible for transferring load and maintaining integrity between the components. Keeping this into consideration, the effectiveness of a straightforward but productive technique of using an additional adhesive layer between the face-sheet and core for improving the damage resistance of sandwich structures is investigated. Contribution of a reinforced skin-core interface via adhesive bonding on the impact and post-impact performances, i.e., the maximum load and energy dissipation capacities and failure modes of the sandwich composites were experimentally investigated. Application of additional adhesive at the skin-core interface while manufacturing CFRP/end-grain balsawood sandwich composite demonstrated improved structural performance with no significant variation in density nor requiring additional complex manufacturing procedures. Experimental methods such as low-energy impact, compression-after-impact (CAI), and core compression tests were utilized to illustrate the influence of the interface enforcement. Experimental results indicate that interface adhesive application reinforces the structure's impact tolerance and improves post-impact response. Controlled skin-core debonding primarily attributes to the improved features.

Acrylonitrile–Butadiene–Styrene (ABS) is a very significant and widely used amorphous thermoplastic that possesses high impact resistance, toughness, and heat resistance. Bending collapse is a predominant failure of polymeric structural members in the vehicle environment under angled and unsymmetrical collisions. Therefore, it becomes critical to investigate the flexural behavior of the ABS beam and find its energy absorption capabilities under a transverse loading scenario. Four-point bending tests were carried out at different strain rates and at two different span lengths to investigate the deformation behavior of ABS. This paper examines the influence of strain rate, friction coefficient, Generalized Incremental Stress-State MOdel (GISSMO) and Damage Initiation and Evolution (DIEM) damage models, yield surfaces, and the span length on the four-point flexural behavior of the ABS polymeric material. A Semi-Analytical material model (SAMP_1) in LSDYNA was utilized to numerically evaluate the behavior of ABS under four-point bending. From extensive investigative explorations, it was found that the flexural behavior of ABS is dependent upon the span length, loading strain rate, and friction coefficient between the specimen and the supports. The modeling of damage was successfully exemplified by using the inherent damage law of the SAMP-1 material model, GISSMO, and DIEM damage formulations.

Acrylonitrile-Butadiene-Styrene (ABS) is an important terpolymer that find applications in numerous engineering fields due to its high impact resistance. Thereby, the experimental characterzation and numerical validation of its impact behavior is the main focus of this investigation. Impact tests were carried out using hemi-spherical impactor at three velocities of 4.43 m/s, 5.775 m/s and 6.264 m/s, respectively. The localized material change caused by microvoids was noticed near the impact zone on non-impacted surfaces for all impact velocities. The damage morphologies on the non-impacted surface for 4.43 m/s includes plastic deformation and crazes without any micmvoids, whereas a combination of crazes and microvoids were discovered for other two velocities. Tensile tests at various strain rates, compression and shear tests were performed on ABS material at quasi-static conditions to utilize as an input to the SAMP-1 material model in impact simulations. The predicted impact histories and damage morphologies were compared with the experimental results.

Carbon fiber composite materials are being used at an increasing rate in the automotive industry due to their low densities, superior mechanical properties and great design flexibilities. The recently developed High Pressure Resin Transfer Molding (HP-RTM) process enables high resin injection rates and thereby shortens composite molding cycle times to meet the demanding performance and volume production requirements of automotive components. However, variability is endemic in composite materials and their processing. The development of an accurate injection simulation model of the HP-RTM process is critical for robust process design. In this paper, uncertainty quantification (UQ) for the simulation of the resin injection process of a carbon fiber composite is developed to predict the resin flow and thus the outcome of the composite molding. The uncertainty interplay is modeled using polynomial chaos expansions (PCE). Several material and molding process parameters have been considered for stochastic analysis. This multi-variable stochastic manufacturing problem is challenging to solve computationally, and a previously developed basis adaptation scheme has been used to reduce the computational effort. The UQ development has been implemented on the GM high performance computing system, and the coupled UQ toolbox PAM-COMPOSITETM injection simulations have been conducted for an automobile underbody floor. The numerical results show an excellent convergence of the PCE methodology for the chosen injection problem. A hypothesis of predicting the occurrence of potential dry spots indirectly, by monitoring the information about the resin arrival time, the value of pressure increase, and the value of saturation pressure at a location in the proximity of the flow front closure has been proposed and validated.

As Light weighting is the top priority for the automotive industry today, the push for reducing overall vehicle weight will likely include the consideration of materials that have not previously been part of mainstream vehicle design and manufacturing, including carbon fiber composites. Therefore, the deformation characteristics and crush performance of carbon fiber reinforced polymer (CFRP) and steel front bumper crush-can (FBCC) assemblies in Quarter-point Impact Tests are investigated in this article. The experimental tests in this study were conducted using a sled-on-sled testing method. Force-time histories, kinematic data and videos for each test were recorded using several high-speed cameras (HSCs), accelerometers and a load cell wall. The collected data was filtered with SAEJ211 CFC 180 filter and sorted to ease the comparative analysis for the performance of the steel and CFRP bumper assemblies. A similar pattern was observed in the crashworthiness characteristics (i.e. force-time history, force-displacement, crash pulse and deformation patterns) of all steel and CFRP FBCC specimens. Typical failure modes of composite bumper assemblies, which were revealed by the high-speed videos were the failure of crush-can and failure of the bumper beam due to the generation of high stresses as it gets stretched due to its curvature after hitting the sled. On the contrary, local permanent deformation of the beam and crush-can was the predominant failure mode in steel FBCCs assemblies under quarter-point loading. Results obtained from the comparative investigation show that CFRP is a more efficient yet lighter material in regard to the absorption of the impact energy.

Structural systems developed from novel materials that are more durable and less prone to maintenance during the service lifetime are in great demand. Due to many advantages such as being lightweight as well as having high strength, corrosion resistance, and durability, the sandwich composites structures, in particular, have attracted attention as favorable materials for speedy and durable structural constructions. In the present research, an experimental investigation is carried out to investigate the flexural response of sandwich beams with a pre-cracked core-upper facesheet interface located at one end of the beam. During the development of the sandwich beams, an initial pre-cracked debond was created between the core and facesheet by placing a Teflon sheet at the interface. Both three-point and four-point flexural tests were conducted to characterize the flexural behavior of the sandwich beams. The effects of the loading rate, core thickness, and placement of the initial interfacial crack under a compressive or tensile stress state on the response and failure mechanism of Carbon Fiber-Reinforced Polymer (CFRP)/Polyurethane (PU) foam sandwich beams were investigated. It was found that the crack tip of the initial debonding between the upper facesheet and the core served as a damage initiation trigger followed by the fracture failure of the core due to the growth of the initial crack into the core in an out-of-plane mode. Finally, this leads to facesheet damage and rupture under flexural loadings. An increase in the core thickness resulted in a higher peak load, but the failure of the sandwich beam was observed to occur at significantly lower displacement values. It was found that the behavior of sandwich beams with higher core thickness was loading rate-sensitive, resulting in stiffer response as the loading rate was increased from 0.05 to 1.5 mm/s. This change in stiffness (10–15%) could be related to the squeezing of all pore space, resulting in the collapse of cell walls and thereby making the cell behave as a solid material. As a result, the occurrence of the densification phase in thick core beams occurs at a faster rate, which in turn makes the thick cored sandwich beams exhibit loading rate-sensitive behavior.

Fiber-reinforced composites are widely used for structural components in the aircraft, automotive, marine, and other industries due to their low density, high specific stiffness and strength, excellent durability, and design flexibility. During the fabrication of continuous fiber reinforced composite components, fiber direction changes, residual stresses, and out-of-the-mold deformations are unavoidable. As the 2-D fabric is deformed to a 3-D part geometry the fiber tows move, leading to fiber direction changes that result in relative angle changes between the fibers that make up the fabric. These changes have a significant effect on the behavior of the composite material system. The extent of fiber angle change in a non-crimp fabric system is largely dependent on the differences between the 2-D and 3-D geometries and the particular stitching parameters used to manufacture the fabric. In order to better understand the influence of fabrication induced fiber angle change on the performance of structural composite parts, detailed experiments and simulations were conducted. For the experiments, a reinforcement geometry was selected. Due to the complexity of the chosen geometry for draping, several slits were designed at strategic locations to allow the fabric to take the shape without wrinkling. During molding, two patterns were overlaid so that the slit locations after molding were staggered through the thickness to reduce their effect on the structural performance. Detailed draping analyses were performed taking into account the process steps, and the fiber angle changes were calculated using numerical models that were developed previously. Further, the fiber angles following draping were mapped onto the structural performance models used to simulate the crush tests. The predicted stiffness and strength results from the integrated fabrication and performance simulations were compared with the experimental measurements, and the correlations are presented in this paper.

Single hat sectioned hybrid beams composed of aluminum and Carbon Fiber Reinforced Polymeric materials (CFRP), intended for structural applications in the automotive and aviation sectors, have been studied from the point of their energy absorption capabilities when submitted to transverse low-velocity impact loading. Carbon fiber-epoxy composite prepregs were placed on the inside of the single hat sectioned aluminum sheet and completely cured in the autoclave under the recommended curing cycle. The bonding process between the aluminum sheet and composite layers was achieved by using 3M VHB™ 4930 double-sided acrylic foam tape. Bonding the aluminum and composite layers through adhesive tape eliminates the requirement of surface preparation of the aluminum layer through chemical etching or mechanical abrasion and thereby the strength of the metallic layer is not reduced due to the formation micropores during the chemical etching process. Results are shown in terms of load-displacement and damage morphologies diagrams; characteristic trends are compared and discussed. It was observed that the presence of viscoelastic adhesive tape material restricts the rupture (visual cracks) failure of the outer aluminum layer, resulting in the only impact-induced indentation for all impact energies. Numerical simulations were also performed to characterize and predict the failure mechanism of such hybrid beams when subjected to impact loading. Numerical predictions showed good correlation with experimental results for all impact histories at low and medium impact energies but a showed slight discrepancy for highest impact energy and were not able to successfully capture the system response in the unloading region. Current modeling does not consider damage healing or recovery with unloading and it is difficult to account for such change in material state. This study provides the low-velocity impact characteristics and collapse behavior of the hybrid hat sectioned beams under tensile and shear forces developed by impact loading by providing insight to their primary damage mechanisms relative to the impact energies. It was found that the primary damage of the specimen’s changes from impact-induced indentation, minimal fiber breakage to partial perforation accompanied by larger indentation depth as the impact energy is increased from 6 to 12 J.

Time-dependent behavior is characteristic of adhesively bonded structureswhen put under constant load (creep). In this study, adhesively bonded beam specimens prepared by adhesively bonding two unidirectional carbon fiber laminated beams were subjected to accelerated three-point bending creep tests. A three-point bending test was selected because of its simplicity and the fact that bending stresses tend to develop in structures under load even if not subjected to direct flexural load. The aim of this study is to predict the long-term behavior and to investigate the long-term creep response of the adhesively bonded composite system. The long-term creep behavior was predicted by time-temperature superposition principle (TTSP) and construction of the master curve at a reference temperature.

Acrylonitrile-butadiene-styrene (ABS) is an extensively utilized rubber-toughened amorphous thermoplastic in industry. Compared to other amorphous thermoplastics, the most promising mechanical quantity of ABS is its high impact resistance. Thus, understanding the mechanical response of ABS to multiaxial loads is of the great industrial concern. The primary objective of this study was to characterize the flexural response of ABS by conducting three-point bending tests at two distinct deformation rates of 5 and 10 mm/s to figure out the deformation rate effect on the flexural response of ABS. It was observed that the ABS act stiffer with an increased deformation rate. Numerical implementation of three-point bending tests for each deformation rate was performed using the semi-analytical material model (SAMP-1) available in Ls-Dyna finite element code. The simulations for each deformation rate were run depending on SAMP-1 and Von-Misses yield surface formulations to figure out the effect of nonidentical material behavior of ABS in tension, compression, and shear on flexural response. The percentage error in the predicted peak force values considering the compression and shear test data (SAMP-1) and without it (Von Misses) was 3% and 7% for deformation rate of 5 mm/s and 5% and 12% for deformation rate of 10 mm/s. Hence, predicting the flexural behavior of ABS accurately, dissimilar material behavior needs to be taken into consideration. Moreover, associated and nonassociated flow rule effects on the flexural response of ABS were numerically investigated and there was no significant influence observed on the flexural response of ABS.

Advantages such as ultra-lightweighting, parts consolidation, and using newly available fast-curing resin formulations are driving the need to develop improved understanding of carbon fiber composites. Towards this end, the present segment of research is focused on developing a multi-scale model to predict the performance of non-orthogonal woven fabric composites. Woven fabrics (where the fiber tows are orthogonal) are used extensively to manufacture components with complex geometries due to their excellent drapability. However, during draping, the fiber tows in the composite preform reorient themselves to conform to the part geometry (the fiber tows are sheared to become non-orthogonal), and the fiber directions may change drastically compared to the original preform, resulting in significant changes in strength and stiffness of the final composite. The ability to include these processing induced effects in predicting the structural performance of these non-orthogonal fabric composites allows us to improve the accuracy of the prediction and optimize the designs. In this paper, a multi-scale modeling approach was developed to predict the performance of composites made using non-orthogonal woven fabrics. Sample coupons molded with and without a pre-determined amount of shearing were evaluated in tensile and three-point bend experiments, and the numerical predictions were compared with the experimental results. A good correlation was observed, validating the developed model.

Synthetic fibers are mainly considered as a source of reinforcement in many composites that have been studied so far. As a continuous effort is being made in the entire world to develop more sustainable products and systems, fibers obtained from natural sources (hemp, flax, jute, etc.) are being considered as substitutes to the synthetic fibers which are commonly used these days. In this study, the tensile, flexural and interlaminar shear strength properties of hemp fiber composites, bonded with an epoxy matrix, are characterized. Three-point bending tests were conducted on the hemp fiber composites and their failure modes were inspected using micrographs and documented. The short-beam shear method was utilized to investigate the interlaminar shear strength of these composites. Hemp fiber composites were found to have considerably lower flexural strength as compared to typical glass fiber/epoxy composites. Lastly, multiscale analyses were performed for the tensile case to predict the response of these composites by conducting simulations at fiber tows and matrix level rather than using typical finite element approach of homogenized properties at ply level with Altair's multiscale designer software (MDS). In the multiscale macro-simulations, a unit cell with twill weave configuration was developed, and the response of the unit cell under tensile loadings was compared to the experiment results. Excellent Correlation was achieved between numerical and experimental results for unnotched tension/compression MDS macro-simulation. A parametric study was conducted to investigate the effect of fiber tow minor radius on the tensile response of the hemp/epoxy composites keeping rest of the geometric parameters of unit cell similar. The smaller minor tow radius predicted higher yield and ultimate strengths as compared to larger ones. A stochastic analysis was also performed to investigate the effects of variations in the geometric unit cell parameters on the young's modulus of hemp/epoxy composite.

Fiber metal laminates (FML) combine the strength of carbon fiber composite layer with ductility of the aluminum layer for desirable mechanical characteristics. For these composites, progressive failure behavior can be complex and require attention. In this study, two carbon fiber reinforced aluminum laminates (CARRAL) with a 3/2 configuration, with aluminum in the outer layer for the first case and one with carbon fiber composite layer in the outer layer were prepared using a vacuum press without any adhesive layer between the layersa significant departure from similar aerospace materials. Epoxy from the prepreg provides adequate adhesion during consolidation in these lower cost FMLs with a pressure level of 0.35MPa. Three-point flexural behaviors of these two material systems were evaluated under static loading and failure modes were recorded. Primary failure modes observed were crack in lower aluminum layer, carbon fiber (CFRP) layer fracture and delamination between upper aluminum and CFRP layer. A major contribution of this study was to predict the flexural response of these FMLs using LS-DYNA finite element code. Modeling the progressive damage behavior of FML by considering stress based material failure and shear stress based delamination failure between adjacent layers were key aspects of finite element modeling. Predicted mechanical behavior matches well with experimental results and the progressive nature of damage are recovered in the model.

Fiber metal laminates (FMLs) are hybrid composite structures made of thin sheets of metal alloys and plies of polymeric materials reinforced with fibers. Among various FML, CArbon Fiber Reinforced ALuminum Laminates (CARALLs) are appreciated because of their excellent impact resistance and energy absorption property; for the correct design of components that are intended to exploit such capabilities, the mechanical characterization is very important, not only in quasi-static but also in high strain rate conditions. With this regard, CARALL has received less attention if compared with other FMLs; moreover, conflicting results are found in the literature, as the actual properties depend on a number of parameters. Each type of FML requires a dedicated test campaign for a correct characterization. Hence, this work shows the mechanical characterization of a newly developed CARALL, manufactured in the laboratories of the Wayne State University, that makes no use of adhesives film among layers. Quasi-static and dynamic tensile tests have been carried out on CARALL sheet samples. The dynamic tests were made by a direct version of Split Hopkinson Bar (SHB) at an average strain rate of 300 s(-1); in the work, the difficulty of achieving accurate strain measurements in such tests was also analyzed, concluding that a direct strain measure by image analysis is essential. A finite element model was also used to confirm the validity of the adopted approach. Finally, the specific CARALL here considered is not strain rate sensitive in terms of material strength; on the contrary, it shows a different failure mode if subjected to dynamic rather than quasi-static loading.

The influence of stacking sequence and resin rich (polyester veil cloth) layers, which were used to improve the adhesion between carbon fiber/epoxy (CFRP) and aluminum layers (AL), on the uniaxial tensile response of carbon fiber reinforced aluminum laminates (CARALL) was investigated in this research study. The metal volume fraction was varied to prepare two types of CARALL laminates having a 3/2 configuration with the help of a vacuum press without using any adhesive film. Numerical simulations were performed by utilizing commercially available finite element (FE) code, LS-Dyna to predict the tensile response of these laminates with initialization of predicted thermal residual stresses that developed during curing of laminates. Delamination failure was considered in the numerical simulation by utilizing the well-known B-K mixed-mode damage propagation model. It was found that addition of epoxy resin rich (polyester veil cloth) layers used for enhancement of interfacial bond adhesion and to ensure no separation between AL-CFRP layers increased the tensile strength of CARALL laminates.