Hybrid Titanium Composite Laminates Research Articles

Developing thermoplastic hybrid titanium composite laminates (HTCLS) at room temperature: Low-velocity impact analyses

Hybrid titanium composite laminates (HTCLs) are high-performance light-weight fiber metal laminates (FMLs) that are being increasingly used in various industries such as aeronautical, military, and marine thanks to their optimized fracture toughness, impact resistance, and thermal performance. In the current study, the low-velocity impact (LVI) characteristics of a new generation of thermoplastic (TP) HTCLs at various energy levels are investigated. To do so, Ti-6Al-4 V sheets, carbon fabrics, and ultra-high molecular weight polyethylene (UHMWPE) fabrics are used to fabricate multiple laminates with different fiber types, metal volume fractions, and lamination layups. A low-cost resin infusion process is employed for manufacturing the laminates at room temperature by using a novel liquid thermoplastic methyl methacrylate resin, Elium® 188. Before fabrication, a multi-step surface treatment method is applied on Ti alloy sheets to enhance the interfacial properties between the composite layer and the metal alloy sheet. In addition to TP-HTCLs, equivalent thermosetting (TS) HTCLs with an epoxy resin, Epolam, are fabricated to compare the results and evaluate the possibility of fabricating recyclable TP-FMLs at room temperature with enhanced out-of-plane properties. Impact properties including contact force, deflection, energy parameters, and related damage modes are investigated and presented for each laminate. It is concluded that the newly developed TP-HTCLs can be cured at room temperature and have enhanced impact properties compared to those of TS-HTCLs. Besides, the HTCL with UHMWPE fabrics on its composite sides (before the Ti alloy sheets) performs better in LVI compared to that with carbon fibers on the top and bottom (of its composite core) since UHMWPE exhibits higher strain to failure and fracture toughness compared to carbon fibers.

Novel thermoplastic fiber metal laminates manufactured with an innovative acrylic resin at room temperature

In the current study, the mechanical characteristics of a new generation of thermoplastic fiber metal laminates (FMLs) manufactured by vacuum-assisted resin infusion (VARI) at room temperature are investigated. For this end, Ti-6Al-4V alloy sheets, ultra-high molecular weight polyethylene (UHMWPE) fabric, carbon fabric, and two hybrid laminates with different layups are manufactured by a novel liquid methyl methacrylate (MMA) thermoplastic resin, Elium®. Prior to fabricating and testing, a multi-step surface treatment is followed to improve the bonding strength between the titanium alloy sheets and fiber-reinforced polymer composite (FRPC) laminates. ASTM standard tests are conducted in tension, compression, shear (both intralaminar and interlaminar) as well as flexural to evaluate the mechanical characteristics of the newly developed hybrid titanium composite laminates (HTCLs). The results are compared with those of equivalent monolithic composites as well as traditional FMLs in the literature to determine the possibility of replacing epoxy resins with Elium® for fabricating different types of FMLs, namely HTCLs. In addition, the results are verified by a recently developed homogenization method, that is the mechanics of structure genome (MSG), which is used in parallel with the rule of mixture (ROM) to verify the experimental results of HTCLs and their constitutive FRPC laminates. The results show equivalent mechanical properties of the newly developed HTCLs compared to those of traditional thermoplastic HTCLs with the advantages of fabricating at room temperature, increasing the production rate, eliminating the residual thermal stresses, and the requirement for post-stretching HTCL panels.

Failure Modes in Hybrid Titanium Composite Laminates

Hybrid titanium composite laminates (HTCLs) combine the benefits of thin titanium sheets and fiber-reinforced polymer (FRP) composite laminates to design high performance light-weight materials with optimized impact resistance, fracture toughness, durability, and/or thermal performance. This paper starts with a detailed review of typical failure modes observed in HTCLs. The critical manufacturing process of thin grade II titanium sheets combined with HexPly G947/M18 carbon fiber-reinforced polymer laminates is described in detail. This includes the evaluation of titanium surface preparation techniques, which guarantee good adhesive bonding. A systematic experimental study of different HTCL configurations under tensile loading confirms that the major failure modes are debonding between the titanium sheet and the FRP laminate, matrix cracking in the 90 deg plies of the FRP laminate and interlaminar delamination. The results show that HTCLs made from woven carbon FRP plies show higher ultimate strengths and strain at breaks than HTCLs containing a cross-ply composite core made from unidirectional (UD) prepreg.

Drilling of Hybrid Titanium Composite Laminate (HTCL) with Electrical Discharge Machining.

An experimental investigation was conducted to determine the application of die sinker electrical discharge machining (EDM) as it applies to a hybrid titanium thermoplastic composite laminate material. Holes were drilled using a die sinker EDM. The effects of peak current, pulse time, and percent on-time on machinability of hybrid titanium composite material were evaluated in terms of material removal rate (MRR), tool wear rate, and cut quality. Experimental models relating each process response to the input parameters were developed and optimum operating conditions with a short cutting time, achieving the highest workpiece MRR, with very little tool wear were determined to occur at a peak current value of 8.60 A, a percent on-time of 36.12%, and a pulse time of 258 microseconds. After observing data acquired from experimentation, it was determined that while use of EDM is possible, for desirable quality it is not fast enough for industrial application.

Experimental and numerical analysis of drop-weight low-velocity impact tests on hybrid titanium composite laminates

An experimental and numerical study on low-velocity impact responses on [Ti/0/90] s hybrid titanium composite laminates (HTCLs) is presented. Different energy levels from 10 to 40 J are investigated using a drop-weight instrument and post-impact inspection. An explicit finite element implementation provides a detailed analysis of impact response in composite and titanium layers, respectively. It accounts for interfacial debonding, progressive failure in composite plies and elastic–plastic deformation in titanium. The main failure modes are experimentally and numerically found to be debonding between titanium and composite, matrix cracking and interlaminar delamination. The principal energy-absorbing mechanism is plastic dissipation of the two titanium sheets. The low cost numerical model is able to effectively predict the overall impact response and major failure modes with good accuracy.

Crack growth behavior of internal titanium plies of a fiber metal laminate

Abstract Hybrid Titanium Composite Laminates (HTCL) offer many attractive properties for use on aerospace structures. They have many of the advantages of traditional composites such as good strength and stiffness to weight ratios. Further, the fiber ply orientations can be varied to give desired orthotropic properties. The HTCL also retain some of the advantages of metallics (titanium in particular) such as electrical conductivity, toughness, and bolt-bearing capacity. In an effort to further optimize this class of materials, the objectives of this research was to investigate several potential heat treatments of Ti-15-3 as to their mechanical properties and how they may translate into a more crack resistant HTCL. Stress–strain curves to failure were developed for each of the four heat treatments of Ti-15-3. Then fatigue tests were conducted on the HTCL specimens containing an open center circular hole. Specimens were made using a foil of one of the four heat treatments placed at the mid-section of the laminate. The fatigue tests determined the number of cycles to crack initiation and the subsequent crack growth behavior of the Ti foil. Fatigue testing was conducted at four different stress ranges, all at a stress ratio of 0.1. Dye penetrant enhanced radiography was used to detect the cracks in the internal ply of titanium. Observations were made on the effect of the foil heat treatment on crack growth behavior.

Bearing Strength Analysis of Hybrid Titanium Composite Laminates

This paper presents a finite element model used to predict the bearing strength of hybrid titanium composite fiber-metal laminates. The model is used to examine the effects of material parameters such as titanium content and edge-distance ratio on specific bearing strength. In addition, a three-dimensional progressive failure user material subroutine is implemented into the commercial finite element code ABAQUS to model stiffness degradation in the graphite-polyimide layers of the hybrid laminate. These results are used to optimize the fiber-metal laminate layup by determining to the ideal tradeoff between joint strength and structural weight.

Low-Velocity Impact Response Characterization of a Hybrid Titanium Composite Laminate

The low-velocity impact response of a hybrid titanium composite laminate, known as TiGr, was compared to that of graphite/epoxy composite. The TiGr material comprised of two outer plies of titanium foil surrounding a composite core. The composite core was PIXA-M (a high temperature thermoplastic) reinforced by IM-6 graphite fibers and consolidated by an induction heating process. The impact response of TiGr was characterized by two modes of failure which differed by failure or nonfailure in tension of the bottom titanium ply. The ductility of titanium caused buckling by yielding whereas the brittle adjacent composite ply lead to fracture. The maximum failure force of the material correlated well with the previously reported static flexural data, and the material outperformed the commonly used graphite/epoxy.

Influence of processing methods on the tensile and flexure properties of high temperature composites

In this study, the influence of processing method on the mechanical properties of high temperature polymer matrix composites was evaluated. Three material systems were studied: PEEK(poly-ether-ether-ketone), PIXA-M, and a hybrid titanium composite laminate (HTCL). Two manufacturing processes were considered for consolidation of each material system: autoclave curing and induction heating. The tensile and flexural properties of the induction-heated materials were compared with their counterpart using the autoclave curing. Post fracture analyses were performed using optical and scanning electron micrography. Similarities and differences due to processing methods are discussed with possible reasoning for each, based on results and the post fracture analysis. These results indicate that the induction-heating process has potential as a cost-effective alternative to the autoclave curing process for consolidation of these high temperature composites.

Behaviour of Hybrid Titanium Composite Laminate (HTCL) under In-Plane Loading

The Hybrid Titanium Composite Laminate (HTCL) incorporates the mechanical advantages of existing hybrid composite laminates such as ARALL and GLARE while extending their applications to harsh environments. Hybrid composite laminates, consisting of layers of Titanium Grade 2 foils bonded together with fibre-reinforced prepreg plies, have been tested under fatigue loading. HTCL has proven to possess exceptional strength and fatigue resistance. Degraded stiffness and ultimate resistances are provided through experimental stress-strain response of HTCL laminates, which are compared with predicted results by a laminate analysis code. The roles of mechanical degradation, the static and dynamic behaviour and fatigue properties of HTCL are addressed. The development of damage in HTCL specimens during fatigue is shown including titanium ply cracking, interfacial debonding, and layer failure. These tests provided several parameters in order to calibrate a numerical Lamaitre's Continuous Damage Mechanics (CDM) fatigue model, which resulted in good agreement with experimental data. The influence of the fatigue properties of titanium layers on the fatigue of HTCL is discussed. The performance of HTCL laminates in fatigue is shown superior to that of the monolithic titanium alloy for room-temperature conditions.

Effect of Cross Section Material Distribution on Impact Response of Hybrid Composites

A linear analytical model is proposed to evaluate the magnitude of the impact force as a function of the velocity of the impactor. This model provides a simple tool for estimating the magnitude of the impact load from the impact energy. For hybrid composites subjected to low- and medium-velocity impacts where elastic deformation is assumed, the effect of cross section material distribution on impact response was investigated. For a hybrid metal/polymer laminate and a hybrid titanium composite laminate, the relative position of the laminate plies has a significant effect on the plate deflection under impact loads. For equal a real weight plates, the number of layers in a hybrid composite laminate does not appear to affect the impact resistance. However, the relative material ratio of metal to polymer (or metal to polymeric composite) in hybrid composites significantly affects the impact response. Furthermore, the relative ply thickness in a laminate does not have significant effect on its impact resistance for plates with equal a real weight, but the research shows that the total relative material distribution does significantly affect the impact response. The analysis also shows that the effect of cross section material distribution can be qualitatively evaluated by checking the bending stiffness of the plate.

Fatigue damage mechanisms in advanced hybrid titanium composite laminates

Hybrid Titanium Composite Laminates (HTCL) are a type of hybrid composite laminate with promise for high-speed aerospace applications, specifically designed for improved damage tolerance and strength at high-temperature (350°F, 177°C). However, in previous testing, HTCL demonstrated a propensity to excessive delamination at the titanium/PMC interface following titanium cracking. An advanced HTCL has been constructed with an emphasis on strengthening this interface, combining a PETI-5/IM7 PMC with Ti-15-3 foils prepared with an alkaline-perborate surface treatment. This paper discusses how the fatigue capabilities of the ‘advanced’ HTCL compare to the first generation HTCL which was not modified for interface optimization, in both tension–tension ( R=0.1) and tension–compression ( R=−0.2). The advanced HTCL did not demonstrate a significant improvement in fatigue life, in either tension–tension or tension–compression loading. However, the advanced HTCL proved much more damage tolerant. The R=0.1 tests revealed that the advanced HTCL increased the fatigue life following initial titanium ply damage up to 10× that of the initial HTCL at certain stress levels. The damage progression following the initial ply damage demonstrated the effect of the strengthened PMC/titanium interface. Acetate film replication of the advanced HTCL edges showed a propensity for some fibers in the adjacent PMC layers to fail at the point of titanium crack formation, suppressing delamination at the Ti/PMC interface. The inspection of failure surfaces validated these findings, revealing PMC fibers bonded to the majority of the titanium surfaces. Tension compression fatigue ( R=−0.2) demonstrated the same trends in cycles between initial damage and failure, damage progression, and failure surfaces. Moreover, in possessing a higher resistance to delamination, the advanced HTCL did not exhibit buckling following initial titanium ply cracking under compression unlike the initial HTCL.

Optimization of Surface Treatment and Adhesive Selection for Bond Durability in Ti-15-3 Laminates

The promising mechanical performance of a baseline Hybrid Titanium Composite Laminate (HTCL) inspired an investigation into maximizing the strength and environmental performance of this new aerospace material. This research focused upon finding the strongest and most durably combination of three commercially-available titanium surface treatments (i.e., Pasa-Jell 107TM, Boeing's Sol-Gel, and Turco 5578R) and two polyimide adhesives (i.e., LaRCTM-IAX and FM5R) for use in HTCL. The tests employed the cracked-lap shear (CLS) specimen geometry for fatigue crack growth measurements and also for fracture toughness analyses of the bonded specimens. The CLS geometry models several bonded applications found in the aerospace industry, and it also represents the debonding characteristics of a cracked titanium foil in HTCL. The environmental performance of these six material combinations has been evaluated after 5,000 hours of continuous exposure to either a Hot/Wet environment that subjected the bonded specimens to 160°F (71°C) with relative humidity in excess of 95%, or to a Hot/Dry environment of 350°F (177°C) with a relative humidity of less than 5%. These two exposure environments utilized in this study are the most aggressive long-term environments that the HTCL is projected to experience while in service. Test results showed that the best combination of the titanium surface treatments and the polyimide adhesives in the FMR adhesive used in conjunction with Boeing's Sol-Gel titanium surface treatment. Though the FM5R/Sol-Gel system was the strongest of all combinations, its performance dropped to less than 50% of its original strength after exposure to the Hot/Dry environment. An important finding is that this bonded system did not significantly degrade after exposure to the Hot/Wet environment. The only other material combination that showed substantial bond strength was the FM5R/Pasa-Jell 107 system, though its strength also dropped to less than 50% of its original strength after exposure to the Hot/Dry environment.

Titanium Ply Effects on the Behavior of a Hybrid Thermoplastic Composite Laminate

An experimental-cum-analytical study was undertaken to investigate the mechanical response of four hybrid titanium composite laminate (HTCL) systems, each prepared using a graphite-fiber-reinforced thermoplastic polyimide as the adhesive in a unidirectional prepreg. Two of the four HTCL systems were fabricated with the titanium Ti15-3 alloy, while the other two systems were fabricated with the titanium Timetal fl-2 I S alloy. The improvement in mechanical properties achieved by the influence of the titanium layer was assessed by comparing the uniaxial tensile results of static strength at room temperature. An analytical study was also performed to predict the laminate strength and loaddeformation behavior based on the constituent material properties. Results included stressstrain curves, ultimate strength, longitudinal modulus, and the description of the observed modes of failure.

An Investigation into the Fatigue of a Hybrid Titanium Composite Laminate

Hybrid composite laminates consisting of layers of metal foils bonded together with fiber-reinforced resin show great promise as a fatigue-resistant material. The hybrid titanium composite laminate (HTCL) incorporates the mechanical advantages of existing hybrid composite laminates such as ARALL and GLARE while extending their applications to elevated temperatures. Titanium layers are bonded by prepreg layers of high-temperature resin reinforced with carbon fibers. The constituent materials used in this study are a metastable β titanium alloy (Ti-15-3), a high-temperature polyimide (LARC™-IAX), and an intermediate modulus carbon fiber (IM7). This study includes quasi-static and fatigue testing of HTCL materials at room temperature and 177°C (350°F). Experimental stress-strain response of HTCL laminates are compared with predicted results by a laminate analysis code called AGLPLY. A stress-based fatigue study was performed to determine the fatigue properties of HTCL laminates. The roles of residual stress in the mechanical behavior and fatigue properties of HTCL are addressed. The development of damage in HTCL specimens during fatigue is shown to include titanium ply cracking, interfacial debonding, and PMC layer failure. The influence of the fatigue properties of titanium layers on the fatigue of HTCL is discussed. The performance of HTCL laminates in fatigue is shown superior to that of the monolithic titanium alloy for room-temperature and elevated-temperature conditions.

High temperature hybrid titanium composite laminates: An early analytical assessment

This paper presents a new type of material system that shows great promise for aerospace applications. The concept consists of thin sheets of titanium bonded together with a polymer composite prepreg consisting of a high temperature resin reinforced with high or intermediate modulus fibers. The potential material performance is outstanding in terms of in-plane fatigue and fracture. As with all composite materials, the exact moduli and strength can be optimized for a given application by varying the constituents, their volume fractions and, in the case of the reinforcing fibers, their orientation. The paper includes analytical studies as well as experimental results.

Preliminary Evaluation of Hybrid Titanium Composite Laminates

In this study, the mechanical response of hybrid titanium composite laminates (HTCL) was evaluated at room and elevated temperatures. Also, the use of an elastic-plastic laminate analysis program for predicting the tensile response from constituent properties was verified. The improvement in mechanical properties achieved by the laminates was assessed by comparing the results of static strength and constant amplitude fatigue tests to those for monolithic titanium sheet. Two HTCL were fabricated with different fiber volume fractions, resin layer thicknesses, and resins. One panel was thicker and was more poorly bonded in comparison to other. Consequently, the former had a lower tensile strength, while fewer cracks grew in this panel and at a slower rate. Both panels showed an improvement in fatigue life of almost two orders of magnitude. The model predictions were also in good agreement with the experimental results for both HTCL panels.