Blog

Damage tolerance testing of sandwich composites: The sandwich CAI test | CompositesWorld

The EHang unmanned aerial vehicle (UAV) complies with approved type design, safety and quality requirements, with deliveries to customers now underway.

Overair heads to flight testing in early 2024, marked by rapid prototype development.  Insulated Precast Concrete Wall Panels

Damage tolerance testing of sandwich composites: The sandwich CAI test | CompositesWorld

The eVTOL developer is scouting locations in the U.S. for continued flight testing of its inaugural consumer aircraft, AIR One, through the Agility Prime program.

Together, the two Spanish companies will outline plans for eVTOL aircraft and operations integration in Europe and Latin America to ensure compatible interaction and maximize aircraft performance.

Following DOA approval, Lilium shifts from the design phase to industrialization, including fuselage matching and joining and a ramp-up of parts production from Tier 1 aerospace suppliers.

The composites-intensive electric aircraft was purchased to meet the airline’s goal of flying a commercial demonstrator by 2026.

A new ASTM-standardized test method established in 2022 assesses the compression-loaded damage tolerance of sandwich composites.  

Composites automation specialist increases access to next-gen technologies, including novel AFP systems and unique 3D parts using adaptive molds.

Combined LSAM and five-axis CNC milling capabilities will optimize D-Composites’ production services, flexibility and cut time and cost for composite tooling manufacture.

Evaluation of CFRTP m-pipe through Element’s U.K. facility aims to qualify the system for new operating environments.

Innovative prepreg tooling is highly drapable, capable of forming complex carbon fiber tooling shapes, in addition to reducing through thickness porosity and only requiring one debulk during layup.

Simutence and Engenuity demonstrate a virtual process chain enabling evaluation of process-induced fiber orientations for improved structural simulation and failure load prediction of a composite wing rib.

Backed by previous composites-related projects, Kineco continues to contribute its expertise to future space exploration in India.

Among the latest advances are toxicity tests, used to evaluate the effect of different resins and plastic degrading on aquatic and terrestrial organisms, and thus determine the technology’s long-term sustainability.  

Breiana Whitehead, pioneering Australian kite-foil sailor, spearheads board design intricacies with ATL Composites to enhance her performance ahead of the July 2024 competition.

Composites automation specialist increases access to next-gen technologies, including novel AFP systems and unique 3D parts using adaptive molds.

New support will enable climate-friendly, high-performance and aesthetically pleasing interiors made from ekoa natural fiber composite surfaces and panels.

Holding the new Guinness World Record at 11.98 meters, the 3D-printed composite water taxi used a CEAD Flexbot to print two hulls in less than 12 days.

Breiana Whitehead, pioneering Australian kite-foil sailor, spearheads board design intricacies with ATL Composites to enhance her performance ahead of the July 2024 competition.

Three prefabricated, low-carbon homes, using Mighty Buildings’ large-format 3D printing and UV-curable resins, will be built in the San Francisco Bay Area as models for future industry developments. 

T50B masterbatch by Mechnano, in partnership with Bomar, streamlines AM resin development, resolving CNT dispersion issues and elevating mechanical performance while catering to various printing technologies

Composites automation specialist increases access to next-gen technologies, including novel AFP systems and unique 3D parts using adaptive molds.

Plastics and composites manufacturers will benefit from Roctool’s heat and cooling induction for molding processes, with increased technical service support and capability demonstrations on a global scale.

Cygnet Texkimp’s Multi Roll Stack and composite recycling technology catalyze ASCEND program’s mission to optimize aerospace, automotive hydrogen storage and CFRP sustainability.

CW explores key composite developments that have shaped how we see and think about the industry today.

Knowing the fundamentals for reading drawings — including master ply tables, ply definition diagrams and more — lays a foundation for proper composite design evaluation.

As battery electric and fuel cell electric vehicles continue to supplant internal combustion engine vehicles, composite materials are quickly finding adoption to offset a variety of challenges, particularly for battery enclosure and fuel cell development.  

Performing regular maintenance of the layup tool for successful sealing and release is required to reduce the risk of part adherence.

Increasingly, prototype and production-ready smart devices featuring thermoplastic composite cases and other components provide lightweight, optimized sustainable alternatives to metal.

The composite pressure vessel market is fast-growing and now dominated by demand for hydrogen storage.

The burgeoning advanced air mobility (AAM) market promises to introduce a new mode of transport for urban and intercity travelers — particularly those who wish to bypass the traffic congestion endemic to the world’s largest cities. The electric vertical take-off and landing (eVTOL) aircraft serving this market, because they depend on battery-powered propulsion, also depend on high-strength, high-performance composite structures produced at volumes heretofore unseen in the aerospace composites industry. This CW Tech Days will feature subject matter experts exploring the materials, tooling and manufacturing challenges of ramping up composites fabrication operations to efficiently meet the demands of a challenging and promising new marketplace.

Manufacturers often struggle with production anomalies that can be traced back to material deviations. These can cause fluctuations in material flow, cooling, and cure according to environmental influences and/or batch-to-batch variations. Today’s competitive environment demands cost-efficient, error-free production using automated production and stable processes. As industries advance new bio-based, faster reacting and increased recycled content materials and faster processes, how can manufacturers quickly establish and maintain quality control? In-mold dielectric sensors paired with data analytics technology enable manufacturers to: Determine glass transition temperature in real time Monitor material deviations such as resin mix ratio, aging, and batch-to-batch variations throughout the process Predict the influence of deviations or material defects during the process See the progression of curing and demold the part when the desired degree of cure, Tg or crystallinity is achieved Document resin mix ratios using snap-cure resins for qualification and certification of RTM parts Successful case histories with real parts illustrate how sensXPERT sensors, machine learning, and material models monitor, predict, and optimize production to compensate for deviations. This Digital Mold technology has enabled manufacturers to reduce scrap by up to 50% and generated energy savings of up to 23%. Agenda: Dealing with the challenge of material deviations and production anomalies How dielectric sensors work with different composite resins, fibers and processes What is required for installation Case histories of in-mold dielectric sensors and data analytics used to monitor resin mixing ratios and predict potential material deviations How this Digital Mold technology has enabled manufacturers to optimize production, and improve quality and reliability

SolvaLite is a family of new fast cure epoxy systems that — combined with Solvay's proprietary Double Diaphragm Forming technology — allows short cycle times and reproducibility. Agenda:  Application Development Center and capabilities Solutions for high-rate manufacturing for automotive Application examples: battery enclosures and body panels

OEMs around the world are looking for smarter materials to forward-think their products by combining high mechanical performance with lightweight design and long-lasting durability. In this webinar, composite experts from Exel Composites explain the benefits of a unique continuous manufacturing process for composites profiles and tubes called pull-winding. Pull-winding makes it possible to manufacture strong, lightweight and extremely thin-walled composite tubes and profiles that meet both demanding mechanical specifications and aesthetic needs. The possibilities for customizing the profile’s features are almost limitless — and because pull-winding is a continuous process, it is well suited for high volume production with consistent quality. Join the webinar to learn why you should consider pull-wound composites for your product. Agenda: Introducing pull-winding, and how it compares to other composite manufacturing technologies like filament winding or pultrusion What are the benefits of pull-winding and how can it achieve thin-walled profiles? Practical examples of product challenges solved by pull-winding

Composite systems consist of two sub-constituents: woven fibers as the reinforcement element and resin as the matrix. The most commonly used fibers are glass and carbon, which can be processed in plane or satin structures to form woven fabrics. Carbon fibers, in particular, are known for their high strength/weight properties. Thermoset resins, such as epoxies and polyurethanes, are used in more demanding applications due to their high physical-mechanical properties. However, composites manufacturers still face the challenge of designing the right cure cycles and repairing out-of-shelf-life parts. To address these issues, Alpha Technologies proposes using the encapsulated sample rheometer (premier ESR) to determine the viscoelastic properties of thermosets. Premier ESR generates repeatable and reproducible analytical data and can measure a broad range of viscosity values, making it ideal for resins such as low viscous uncured prepreg or neat resins as well as highly viscous cured prepregs. During testing, before cure, cure and after cure properties can be detected without removing the material from the test chamber. Moreover, ESR can run a broad range of tests, from isothermal and non-isothermal cures to advanced techniques such as large amplitude oscillatory shear tests. During this webinar, Alpha Technologies will be presenting some of the selected studies that were completed on epoxy prepreg systems utilizing ESR and how it solves many issues in a fast and effective way. It will highlight the advantages of this technique that were proven with the work of several researchers. Moreover, Alpha Technologies will display part of these interesting findings using the correlations between the viscoelastic properties such as G’ and mechanical properties such as short beam shear strength (SBS).

Surface preparation is a critical step in composite structure bonding and plays a major role in determining the final bonding performance. Solvay has developed FusePly, a breakthrough technology that offers the potential to build reliable and robust bonded composite parts through the creation of covalently-bonded structures at bondline interface. FusePly technology meets the manufacturing challenges faced by aircraft builders and industrial bonding users looking for improved performance, buildrates and lightweighting. In this webinar, you will discover FusePly's key benefits as well as processing and data. Agenda: Surface preparation challenges for composite bonding FusePly technology overview Properties and performance data

The annual Conference on Composites, Materials, and Structures (also known as the Cocoa Beach Conference) is the preeminent export controlled and ITAR restricted forum in the United States to review and discuss advances in materials for extreme environments. The Conference started in the 1970s as a small informal gathering for government and industry to share information on programs and state-of-the-art technology. Attendance has grown to nearly 500 people while preserving this same objective to share needs and trends in high-temperature and extreme environment materials, and the latest information on advanced materials and manufacturing processes. The five-day conference program includes two to three parallel sessions per day on topics including thermal protection materials, ceramic matrix composites, carbon-carbon materials, ballistic technologies, hypersonics, and gas turbine engines. Attendees are engineers, scientists, managers, and operational personnel from the turbine engine, aviation, missiles and space, and protective equipment communities. These communities include the Navy, Air Force, Army, MDA, NASA, DARPA, FAA, DOE, engine manufacturers, missile and aircraft manufacturers, commercial space companies, and material and component suppliers. The Conference will be held in St. Augustine again for 2024! Participation is limited to U.S. Citizens and U.S. Permanent Residents only with an active DD2345 certification.

The 48th International Conference & Exposition on Advanced Ceramics & Composites (ICACC 2024) will be held from Jan. 28–Feb. 2, 2024, in Daytona Beach, Fla. It is a great honor to chair this conference, which has a strong history of being one of the best international meetings on advanced structural and functional ceramics, composites, and other emerging ceramic materials and technologies.

Venue ONLY ON-SITE @AZL Hub in Aachen Building Part 3B, 4th Floor Campus Boulevard 30 52074 Aachen Time: January 31st, 2024 | 11:00-16:00h (CET) This first constitutive session will shape the future of the workgroup. ✓ Insights into solutions for e.g. circularity, recycling, sustainability, end of life etc. ✓ Interactive exchange along the value chain to tackle these challenges: Share your input in the “World Café” workshop session! ✓ Are you a solution provider? Take your chance and present your solution approach in a short 5-minute pitch. Get in touch with Alexander.  

The Transformative Vertical Flight (TVF) 2024 meeting will take place Feb. 6–8, 2024 in Santa Clara, California, in the heart of Silicon Valley and will feature more than 100 speakers on important progress on vertical takeoff and landing (VTOL) aircraft and technology. 

The Program of this Summit consists of a range of 12 high-level lectures by 14 invited speakers only. Topics are composite related innovations in Automotive & Transport, Space & Aerospace, Advanced Materials, and Process Engineering, as well as Challenging Applications in other markets like Architecture, Construction, Sports, Energy, Marine & more.

JEC World in Paris is the only trade show that unites the global composite industry: an indication of the industry’s commitment to an international platform where users can find a full spectrum of processes, new materials, and composite solutions.

Thousands of people visit our Supplier Guide every day to source equipment and materials. Get in front of them with a free company profile.

Cevotec, a tank manufacturer, Roth Composite Machinery and Cikoni, have undertaken a comprehensive project to explore and demonstrate the impact of dome reinforcements using FPP technology for composite tanks.   

Initial demonstration in furniture shows properties two to nine times higher than plywood, OOA molding for uniquely shaped components.

The composite tubes white paper explores some of the considerations for specifying composite tubes, such as mechanical properties, maintenance requirements and more.

Foundational research discusses the current carbon fiber recycling landscape in Utah, and evaluates potential strategies and policies that could enhance this sustainable practice in the region.

In its latest white paper, Exel navigates the fire, smoke and toxicity (FST) considerations and complexities that can influence composites design.

New white paper authored by Eike Langkabel, Sebastian de Nardo, and Jens Bockhoff, examines the best resin formulations for composites used in automotive part production, both structural parts and body panels.

Online industry event in spring 2024 will feature six presentations covering sustainability in the composites industry.

Austrian research institute Wood K plus makes 95% silicon carbide ceramics more sustainable (>85% bio/recycled content), enables 3D shapes via extrusion, injection molding and 3D printing.

Thermoplastic polymer resin was designed to tackle distinctive industry challenges of large-scale 3D printing while also assisting with sustainability initiatives.

The MB9, representing a combination of high performance and eco-conscious materials use, will be commercially available in time for the 2024 sailing season.

For 42 months, the Aitiip Technology Center will coordinate the EU-funded project to design a new range of intermediate materials, such as pellets or resin-impregnated carbon fibers, which will be used to manufacture more sustainable final products.

Co-located R&D and production advance OOA thermosets, thermoplastics, welding, recycling and digital technologies for faster processing and certification of lighter, more sustainable composites.

Closed mold processes offer many advantages over open molding. This knowledge center details the basics of closed mold methods and the products and tools essential to producing a part correctly.

In the Automated Composites Knowledge Center, CGTech brings you vital information about all things automated composites.

Explore the cutting-edge composites industry, as experts delve into the materials, tooling, and manufacturing hurdles of meeting the demands of the promising advanced air mobility (AAM) market. Join us at CW Tech Days to unlock the future of efficient composites fabrication operations.

The composites industry is increasingly recognizing the imperative of sustainability in its operations. As demand for lightweight and durable materials rises across various sectors, such as automotive, aerospace, and construction, there is a growing awareness of the environmental impact associated with traditional composite manufacturing processes.

CW’s editors are tracking the latest trends and developments in tooling, from the basics to new developments. This collection, presented by Composites One, features four recent CW stories that detail a range of tooling technologies, processes and materials.

CompositesWorld’s CW Tech Days: Infrastructure event offers a series of expert presentations on composite materials, processes and applications that should and will be considered for use in the infrastructure and construction markets.

During CW Tech Days: Thermoplastics for Large Structures, experts explored the materials and processing technologies that are enabling the transition to large-part manufacturing.

This CW Tech Days event will explore the technologies, materials, and strategies that can help composites manufacturers become more sustainable.

CompositesWorld’s CW Tech Days: Infrastructure event offers a series of expert presentations on composite materials, processes and applications that should and will be considered for use in the infrastructure and construction markets.

Explore the cutting-edge composites industry, as experts delve into the materials, tooling, and manufacturing hurdles of meeting the demands of the promising advanced air mobility (AAM) market. Join us at CW Tech Days to unlock the future of efficient composites fabrication operations.

Thermoplastics for Large Structures, experts explored the materials and processing technologies that are enabling the transition to large-part manufacturing.

MVP's Automated Equipment: Revolutionizing Composites Part Production Through Filament Winding within CompositesWorld's CompositesWorld Collections Knowledge Center

Composites One Offers Manufacturing Efficiencies with Aerovac Kitting Solutions within CompositesWorld's CompositesWorld Collections Knowledge Center

A report on the demand for hydrogen as an energy source and the role composites might play in the transport and storage of hydrogen.

This collection features detail the current state of the industry and recent success stories across aerospace, automotive and rail applications.

This collection details the basics, challenges, and future of thermoplastic composites technology, with particular emphasis on their use for commercial aerospace primary structures.

This collection features recent CW stories that detail a range of tooling technologies, processes and materials.

A new ASTM-standardized test method established in 2022 assesses the compression-loaded damage tolerance of sandwich composites.  

Figure 1. ASTM D8287 sandwich CAI test fixture and specimen. Photo Credit, all images: Dan Adams

Damage tolerance testing of composites refers to the testing of specimens with a centrally located damage site, under a specified loading condition. Typically, the damage is produced by drop-weight impacting, which can cause extensive internal damage that is difficult to detect by visual inspection. For composite laminates, damage tolerance testing is typically performed under in-plane compression loading because their compression strengths are lower than their tension strengths and, therefore, more critical in many designs. Additionally, impact damage typically has a greater effect on the compression strength. The ASTM D71371 test method, initially standardized in 1999, is commonly followed for determining the compression-after-impact (CAI) strength of composite laminates. Until recently, however, considerably less emphasis has been placed on developing standardized damage tolerance test methods for sandwich composites.

In 2011, ASTM International (West Conshohocken, Pa., U.S.) published a standardized practice for damage resistance testing of sandwich composites, ASTM D77662, which provides supplemental instructions for imparting damage to sandwich composite specimens following either ASTM D62643 for quasi-static indentation (Procedures A and B) or ASTM D71364 for drop-weight impact testing (Procedure C). In 2022, two new sandwich damage tolerance test methods were standardized: a sandwich CAI test and a sandwich flexure-after-impact (FAI) test. In this column, we’ll focus on the new compression-loaded damage tolerance test method for sandwich composites, ASTM D82875, shown in Fig. 1.

Based on previous research investigations6-9 and a series of experimental evaluations10 performed during test method development, a standard sandwich CAI specimen size of 215 millimeters in width and 265 millimeters in length was established. These specimen dimensions were increased in relation to the 100-millimeter-wide and 150-millimeter-long laminate CAI specimen to allow for the larger damage areas produced in sandwich composites and to accommodate the use of strain gages for specimen alignment. Although quasi-isotropic laminates are typically used for laminate CAI testing, the facesheet ply layup and core configuration for sandwich composite CAI specimens are often selected to represent the intended structural application. In some cases, however, the core thickness must be increased to avoid specimen buckling under compression loading. Additionally, potting of the core region at the specimen ends may be required to avoid facesheet separation or end-brooming prior to specimen failure.

Figure 2. ASTM D8287 standard specimen configuration (all dimensions are in millimeters).

Similar to the ASTM D7137 test method for damage tolerance testing of composite laminates, ASTM D8287 requires that the loaded ends of the sandwich specimen are machined parallel within tight tolerances. Four bonded strain gages, mounted onto the facesheets in the loading direction, are used for specimen alignment prior to testing. Based on the results of finite element analyses10, the preferred strain gage placements are 25 millimeters from the specimen outer edges and either 25 millimeters below the top edge of the specimen or 12 millimeters below the upper potted region, whichever is greater. The standard specimen dimensions and strain gage locations are shown in Fig. 2.

The test fixture used for sandwich CAI testing (Fig. 1) is a scaled-up version of the ASTM D7137 laminate CAI test fixture that can accommodate sandwich specimen thicknesses up to 50 millimeters. The end-loading fixture consists of a base, two vertical supports and a top plate. The base and top plate use adjustable, flat-faced specimen supports that provide some restraint to out-of-plane rotation and prevent end-brooming of the facesheets. The vertical supports use adjustable knife-edged specimen side supports that provide out-of-plane restraint to buckling. The height of the vertical supports is reduced to produce a small gap adjacent to the top plate to allow for the reduction in specimen length during compression loading.

After the sandwich specimen is secured into the test fixture, the assembly is placed between the platens of the testing machine and aligned with the loading axis. A locking spherical-seat platen is recommended, but not required, for specimen alignment using the four bonded strain gages. If a spherical-seat platen is not used, shims placed between the fixture and platens may be incorporated for alignment. To align the specimen, the assembly is compression loaded to approximately 10% of the estimated maximum force and the four strain gage readings are obtained. Differences in strain between the gages indicates specimen bending or uneven load introduction. If the difference in the readings exceeds 10%, the specimen is unloaded and the spherical-seat platen locking screws are adjusted. If a spherical platen is not used, shims are inserted between the platens and test fixture. This alignment procedure is repeated until all four strain gage readings are within 10%. The sandwich specimen is then compression loaded at a constant displacement rate and the applied force, crosshead displacement and strain data from the bonded strain gages are recorded. Once the peak force is reached and the measured force drops by more than 30% from the peak value, the loading is halted to help identify the initial failure mode and location for later evaluation. The sandwich CAI strength is calculated using the peak applied force, and the total cross-sectional area of the two facesheets.

Minor end crushing before final failure in the gage section sometimes occurs, but if a valid gage section failure is ultimately achieved, such end crushing does not necessarily invalidate the test —  what does invalidate it, however, is the onset of specimen instability or excessive bending. Gage section failures away from the impact damage are considered acceptable, and may indicate that the specimen is not sensitive to the induced damage, such that it fails at a compressive stress near the specimen’s undamaged strength. While this test method may also be used to test undamaged sandwich specimens for use in experimentally determining strength reductions due to impact damage, care should be taken to prevent undesirable failure modes such as end crushing. Note that the ASTM C36411 sandwich edgewise compression test, originally standardized in 1955, remains the recommended test methods for determining the undamaged sandwich compression strength.

1 ASTM D7137/D7137M-17, “Compressive Residual Strength Properties of Damaged Polymer Matrix Composite Laminates,” ASTM International (W. Conshohocken, PA, US), 2017 (first issued in 2005).

2 ASTM D7766/D7766M-23, “Damage Resistance Testing of Sandwich Constructions,” ASTM International (W. Conshohocken, PA, US), 2023 (first issued in 2011).

3 ASTM D6264/D6264M-23, “Measuring the Damage Resistance of a Fiber-Reinforced Polymer-Matrix Composite to a Concentrated Quasi-Static Indentation Force,” ASTM International (W. Conshohocken, PA, US), 2023 (first issued in 1998).

4 ASTM 7136/D7136M-20 “Measuring the Damage Resistance of a Fiber-Reinforced Polymer Matrix Composite to a Drop-Weight Impact Event,” ASTM International (W. Conshohocken, PA, US), 2020 (first issued in 2005).

5 ASTM D8287/D8287M-22, “Compressive Residual Strength Properties of Damaged Sandwich Composite Panels,” ASTM International (W. Conshohocken, PA, US), 2022.

6 Tomblin, J.S., Raju, K.S., Liew, J., and Smith, B.L., 2001, “Impact Damage Characterization and Damage Tolerance of Composite Sandwich Airframe Structures,” Final Report, DOT/FAA/AR-00/44.

7 Tomblin, J.S., Raju, K.S., and Arosteguy, G., 2004, “Damage Resistance and Tolerance of Composite Sandwich Panels – Scaling Effects,” Final Report, DOT/FAA/AR-03/75.

8 Butterfield, J.M., and Adams, D.O., “Effects of Stitching on Compression After Impact Strength of Sandwich Composites,” Long Beach, CA: Proceeding of the 49th International SAMPE Symposium and Exhibition, 2004.

9 Butterfield, J.M., 2006, “Damage Tolerance of Stitched Carbon Composite Sandwich Structures,” M.S. Thesis, University of Utah.

10 Kuramoto, B., Stanfield, M., and Adams, D.O., “Development and Evaluation of the Sandwich Edgewise Compression After Impact Test,” to appear in the Journal of Sandwich Structures and Materials, 2024.

11 ASTM C364/C364M-16, “Edgewise Compressive Strength of Sandwich Constructions,” ASTM International (W. Conshohocken, PA, US), 2016 (first issued in 1955).

Dr. Donald F. Adams (Wyoming Test Fixtures (Salt Lake City, Utah) takes look at flexural testing and promises recommendations, next time, for a unified standard.

Dr. Don Adams asks and suggests a likely answer to the question Which shear test method is best?

Dan Adams assesses the facesheet or core failures for three-point and four-points flexural loading configurations. 

Dr. Don Adams (Wyoming Test Fixtures Inc., Salt Lake City, Utah) discusses when and why test specimens must be protected by tabs.

A new ASTM-standardized open-hole compression test method seeks to determine the notch sensitivity of sandwich composites. 

A range of standardized mechanical tests for complex composites are available and still under development for materials development, design and quality control requirements. 

While time consuming and somewhat subjective, the comparative assessment approach has been proven effective toward assessing composites test method equivalence.

Damage tolerance testing of sandwich composites: The sandwich CAI test | CompositesWorld

Lightweight Sandwich Panels CompositesWorld is the source for reliable news and information on what’s happening in fiber-reinforced composites manufacturing. Learn More