Benjamin Liaw

Stacking Sequence and Geometrical Effects on Low-Velocity Impact Behaviors of GLARE 5 (3/2) Fiber–Metal Laminates:

Impact responses and damage induced by a drop-weight on GLARE 5 (3/2) fiber–metal laminates (FMLs) with various lay-up configurations were studied experimentally. The effect of specimen geometry was also considered. The damage characteristics were evaluated using both nondestructive ultrasonic and mechanical-sectioning techniques. Only the contour of the entire damage area could be obtained using ultrasonic C-scan, whereas more details of the damage were provided through the mechanical-sectioning technique. The impact properties of FMLs were affected by laminate stacking sequence. The first severe failure induced by low-velocity impact occurred as debonding between aluminum and the adjacent fiber–epoxy layer at the nonimpact side. It was followed by a visible crack in the outer aluminum layer at the nonimpact face. GLARE 5 made of unidirectional fibers had the least impact resistance; followed by cross-ply and angle-ply configurations; while the quasi-isotropic lay-up showed the best in resistance to impact. By introducing circular, rather than square, geometry as the outer perimeter of the specimens, the damage patterns as well as impact behaviors changed due to the relative anisotropy of the specimen with respect to the specimen clamping.

Low-Velocity Impact on GLARE 5 Fiber-Metal Laminates: Influences of Specimen Thickness and Impactor Mass

AbstractImpact response and damage induced by a drop-weight instrument on glass reinforced (GLARE) 5 fiber-metal laminates of different thicknesses were studied. The effect of the impactor mass was also considered. The damage characteristics were evaluated using both the nondestructive ultrasonic and mechanical-sectioning techniques. Only the contour of the entire damage area can be obtained using ultrasonic C-scan; whereas, more details of the damage are provided through the mechanical cross-sectioning technique. Thicker GLARE 5 offers higher impact resistance. It was found that the failure mode changed with varying thickness and impactor mass. Panels that were tested with the lighter impactor mass would reach the perforation limit faster than the panels tested with the heavier impactor mass for the same impact energy. It was observed that the critical behaviors of the fiber and aluminum depended on the thickness of the panel. Threshold cracking energy varied parabolically with respect to the specimen th...

Influences of thickness and stacking sequence on ballistic impact behaviors of GLARE 5 FML plates: Part II – Numerical studies:

This two-part article examines the effects of thickness and stacking sequence of GLARE 5 (2024-T3 aluminum alloy-unidirectional S2-glass/epoxy) fiber–metal laminated (FML) plates subjected to ballistic impact. Part I presented experimental observations of damage development in the specimens, C-scan damage contours, projectile velocity profiles and ballistic limit velocities (V50). Part II concerns with finite element (FE) modeling of the FML plates. The 3D FE code, LS-DYNA, was used to model and validate the experimental results. Experimentally obtained incident projectile impact velocity versus the residual velocity (Vi∼Vr), damage patterns and bullet residual length were used to validate the FE model. Good agreement was achieved between experimental and numerical results. It was found that for a given specimen thickness/stacking-sequence, by increasing the projectile incident velocity up to its V50 value, the maximum contact force increased. By further increasing the projectile velocity above its V50, the maximum contact force was relatively invariant with respect to an increase in the projectile incident velocity.

Effect of Temperature on Mechanical Properties of Nanoclay-Reinforced Polymeric Nanocomposites. I: Experimental Results

AbstractIn this paper, the effect of temperature and nanoclay reinforcement percentage on nanoclay-reinforced polymeric nanocomposites is studied. First, polypropylene (PP 3371) resin reinforced with various nanoclay percentages is tested at room, elevated, and low temperatures. The tests are conducted on ASTM Type I specimens instrumented with strain gauges in a material testing system machine equipped with an environmental chamber. Next, to ascertain the effect of various PP resins, nanoclay-reinforced Borealis and total petrochemical (TP 3868) tensile specimens are tested from low to elevated temperatures. In addition, nanoclay-reinforced epoxy specimens are tested at room temperature. The test results are plotted as stress-strain curves and the mechanical properties of the nanocomposites including the Young’s modulus, Poisson’s ratio, ultimate stress, and failure strain are determined. The tensile test results indicate that the Young’s modulus of the nanocomposite increases with increasing nanoclay re...

An Experimental Study of Self-diagnosis of Interlaminar Damage in Carbon-fiber Composites

An experimental study was conducted to sense interlaminar delamination in carbon-fiber composites utilizing inherent material piezoresistivity. Mode I and II interlaminar fracture tests were carried out on double cantilever beam and end-notched-flexure specimens following ASTM standards. The traditional DC-sourcing two-point probe technique was employed to measure the through-thickness electrical resistance change. For comparison, optical marker method and acoustic emission technique were also applied to detect interlaminar crack growth. The investigation demonstrates the application potential of the self-sensing capabilities of carbon-fiber composites for structural health monitoring.

Ballistic performance of hybrid and non-hybrid composite plates

This paper presents an experimental and numerical study to understand ballistic behavior of plain-weave hybrid and non-hybrid composites. The effect of hybridization on ballistic limit (V50) was investigated. The hybrid S2 glass-IM7 graphite fibers/toughened SC-79 resin, non-hybrid S2 glass-fiber/toughened SC-79 resin, and non-hybrid IM7 graphite fibers/toughened SC-79 resin composites plates were impacted at various velocities. The three-dimensional dynamic nonlinear finite element code, LS-DYNA, modified with a proposed user-defined nonlinear-orthotropic damage model, was adopted to simulate the experimental results. The combined results obtained from experiments and finite element simulations were then used for determining V 50 for each lay-up configuration. Good agreement between experimental and FE results was found from the comparison of dynamic strain and damage patterns. The hybridization found to be very effective on ballistic limit velocities of woven composites.

Drop-Weight Impact Studies of GLARE 5 Fiber-Metal Laminates

Impact responses and damage induced by a drop-weight instrument on GLARE 5 fiber-metal laminates with different layup configurations and geometries were studied. The damage characteristics were evaluated using both the nondestructive ultrasonic and mechanical sectioning techniques. Only the contour of entire damage area could be obtained using ultrasonic C-scan whereas more details of damage were provided through the mechanical cross-sectioning technique. It was found that failure mode changed with varying stacking sequence. GLARE 5 made of unidirectional fibers had the worst impact resistance; followed by cross-ply and angle-ply configurations, while the quasi-isotropic lay-up showed the best resistance to impact. Finally, influence of different geometries was considered. The results show that by introducing circular geometry, damage patterns and impact behaviors were changed. This was especially apparent for panels with the quasi-isotropic layup configuration.

The ECSEL's integrated approach to industry-academe relations

ECSEL, a National Science Foundation (NSF) funded coalition for engineering education, has developed a strong industry tie with a network of industrial partners. The involvement of these partners in the ECSEL project has been voluminous and can be summarized in three words: breadth, depth and continuity. Examples of their efforts are: providing projects for interdisciplinary integration of design; full partnership in the planning, development and implementation of courses; serving on the Industry Advisory Board; hosting tours of manufacturing plants; donation of equipment and software; offering summer co-op opportunities, etc. In short, their contributions include cash, materials, personnel time and, most importantly, their expertise in real-life product development, a task that a new engineering graduate is expected to tackle when entering industry.

Damage Assessments of Ballistic Impact Behaviors of GLARE 5 (3/2) Beams with Various Stacking Sequences

Fiber-metal laminated beams of GLARE 5 (3/2) lay-up configuration of dimensions: 254×25.4mm (10″×1″) with various stacking sequences were impacted by a 0.22 caliber bullet shaped projectile using a high-speed gas gun. The effect of stacking sequence was considered on FMLs with unidirectional [04°], unidirectional [904°], cross-ply [0°/90°]s and quasi-isotropic [0°/±45°/90°] lay-up orientations. Optical imaging and mechanical sectioning techniques were used to assess the impact damages. The results showed that the failure pattern was changed by altering the specimen stacking sequences. A visible longitudinal crack along the 0° fiber direction was observed for the unidirectional [04°] specimen. Subjected to the ballistic impact, damage development in the unidirectional [904°] FMLs caused the specimens to split into two halves. A Phantom V710 high-speed camera was used to monitor the crack propagation and damage growth on the backside of the specimens with unidirectional [04°] and cross-ply [0°/90°]s lay-up sequences. In particular, it was illustrated experimentally that a small circular region of damage was created on the non-impacted side of the specimens. In addition, for the unidirectional specimen, the damage progressed as a lip-shaped zone; whereas, it advanced as a diamond-shaped contour for the cross-ply specimen. The 3D dynamic nonlinear finite element (FE) code, LS-DYNA, was used to validate the experimental results. The finite element results were compared to those obtained experimentally. Good agreement between the experimental and FE result was obtained.

Experimental and Numerical Approaches on Behavior of GLARE 5 Beams: Influences of Thickness and Stacking Sequence

In this study, GLARE 5 fiber-metal laminates (FMLs) of dimensions: 254 mm ×25.4 mm (10″ × 1″) with various stacking sequences and thicknesses were impacted by a 0.22 caliber bullet shaped projectile using a high-speed gas gun. The effect of stacking sequence was considered for the GLARE 5 (3/2) panels with cross-ply [0°/90°]s, unidirectional [04°], unidirectional [904°] and quasi-isotropic [0°/±45°/90°] lay-up orientations; whereas, thickness effect was studied for the GLARE 5 cross-ply panels with various layers. The experimentally obtained incident projectile impact velocity versus the residual velocity was plotted for each type of specimen. The data were then fitted numerically according to the classical Lambert-Jonas equation for the determination of the ballistic limit velocity, V50. The 3D dynamic nonlinear finite element (FE) code, LS-DYNA, was used to validate the experimental results. Excellent agreement between experimental and FE results was found.