TUGAS BEDAH JURNAL 1

 

     Nama               : FATHONI

     NPM                : 22417233

     Kelas               : 3IC05

MATA KULIAH METODOLOGI PENELITIAN

JURUSAN TEKNIK MESIN

FAKULTAS TEKNOLOGI INDUSTRI

UNIVERSITAS GUNADARMA

KALIMALANG

2019

The Discontinuous Carbon Fiber Composite: A Review of the Damage Characteristics

Jefri Bale

Jurusan Teknik Mesin, Fakultas Sains dan Teknik, Universitas Nusa Cendana Jl. Adisucipto, Penfui-Kupang NTT, Indonesia

Email : jefri.semuel@gmail.com

Abstrak

Terputus-putus serat karbon komposit (DCFC) adalah salah satu bentuk produk bahan murah baru yang telah diterapkan untuk komponen komersial seperti bingkai jendela dari Boeing 787 Dreamliner. Studi DCFC sangat menantang karena tidak memiliki perilaku alam yang sama seperti komposit konvensional atau bahan isotropik. Dalam karya ini beberapa penelitian tentang karakteristik kerusakan material DCFC disajikan. Karakteristik kerusakan DCFC diselidiki saat menjalani statis dan kelelahan pembebanan. Secara khusus, mekanisme kerusakan DCFC juga diamati melalui beberapa uji tak rusak metode (NDT). review telah menunjukkan bahwa studi spesimen DCFC memberikan tantangan yang menarik untuk pekerjaan di masa depan untuk memahami karakteristik kerusakan dan keandalan metode NDT untuk mempelajari kerusakan material DCFC.

Kata kunci: karbon terputus-putus serat epoxy komposit (DCFC), Kerusakan, metode NDT.

RESEARCH METHODOLOGY

Material

In this study, we mainly focused on discontinuous (chip form) carbon fiber as the reinforcement and epoxy was employed as the matrix as known as the Hexcel material. In general, the random stacks of chips was then pressed molded and had a fiber content of around 57 % by volume and produced material density of 1.55 g/m³.

Test Set Up

Before performing damage analyses, the DCFC material was tested under static and fatigue loading conditions to determine the mechanical properties and the damage appearances. Then, an analysis had undertaken to evaluate the damage behavior that occurred during static and fatigue test and how damage accumulated throughout the specimens.

RESULTS AND DISCUSSION (BASED ON CASE STUDIES)

The Mechanical and Damage Characteristics

Several previous studies have been performed that focused on mechanical and damage analysis of DCFC.

Boursier and Lopez, 2010 investigated the failure initiation and effect of defects on structural discontinuous carbon fiber composite. It was found that DFC is relatively insensitive to the types and sizes of the defects that affect of to the continuous fiber composite (CFC) and also Initial do not correlate failure load or give a good indication of the final failure location. Fig.2 below shows the experimental results that indicate the behavior of DFC material.

Fig. 1 Failure and insensitive of DCFC (Boursier and Lopez, 2010)

The several studies about the mechanical behavior of discontinuous carbon fiber composite were also performed by Ferabolli et.al (2009, 2010). In their research about the characterization of DFC for Aerospace application, the chip dimensions of 50 mm in length and 8 mm in width gives a good compromise between mechanical performance and manufacturing ability. The results of tensile test shown that the failure of the DFC are the combination of two failure modes: cracking caused separation along the surface that perpendicular to the chip axis and delamination caused separation along the thickness that parallel to the chip length. The comparison between flexural strength, compressive and tensile strength indicating the different behavior from continuous fiber laminates. Flexural strength of DFC is the highest, followed by compressive, and then tensile strength which continuous quasi-isotropic always have the lowest compressive strength, tensile and flexural strength are usually closer together. These static strengths of DFC highly influenced by the fiber / chip length. Fig.3 below shows the result of different static strength of DFC as a function of fiber length.

Fig. 2 Ultimate strength of DCFC for different load type (Ferabolli et.al, 2009)

The effect of specimen condition (with and without hole) on elastic tensile behavior and failure responsetor this DFC material also investigated by Feraboli et.al, 2009. For Unnotched specimen, under tensile loading, the specimen fails in a combination of chip disbonding (matrix shearing between the chips) and fiber failure as shown in Fig.2 

Fig. 3 Damage of DCFC (Ferabolli et.al, 2009)

For an open hole specimen of DCFC, under tensile loading, the failure behavior shows different failure behavior compared to the composite material in general. The specimen shows insensitive behavior due to an open hole

condition. The failure of specimen occurred in gross area of the surface for certain test with a small hole specimen (Fig.4). The results also confirm that the strength of this DCFC does not decrease with the presence of the hole (Fig.6).

Fig. 4 Failure in gross section (Ferabolli et.al, 2009)

Fig. 5 Variation of notch strength with hole diameter (Ferabolli et.al, 2009)

This uncommon insensitive hole behavior of DCFC possibly due to the internal stress concentration arising from the heterogeneous nature of meso-structure (Qian et.al, 2011 and Bale, 2014). In order to isolate the effects of internal stress concentration from the geometrical stress concentration of hole, a constant hole to width ratio is required to ensure damage at the edge of the hole, generating more distinguishable trends. The critical hole to width ratio threshold for the DCFC material was found to be between 0.25 and 0.375 (Qian et.al, 2011). According to Bale, 2014, During the first fatigue cycles, it occurs an intial rapid increase in damage evolution (an average increase about of 10 % during the first 20 % of the fatigue life). Thereafter, the damage increases slowly until being close to final failure. For the last 5% of fatigue life the damage increases suddenly and strongly as a consequence of final catastrophic failure. Damage evolution indicates that there are three stage of damage evolution in DCFC specimen. Initial micro matrix cracking damage growth of matrix cracking, chip/matrix debonding and chip cracking becomes stable. In the third stage, chip breakage take place and which caused separation along the thickness until the final failure.

DAFTAR PUSTAKA

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